THE RIGHT MENTOR

Tag: Study

Motion and Time | Study
Electric Current and its Effects | Study
Light | Study
Forests: Our Lifeline | Study
Wastewater Story | Study
Heat | Study
Acids, Bases and Salts | Study
Physical and Chemical Changes | Study
Respiration in Organisms | Study
Transportation in Animals and Plants | Study
Reproduction in Plants | Study
CBSE 7 | Science – Study – Free
Nutrition in Plants | Study
Nutrition in Animals | Study
LIGHT | Study
COAL AND PETROLEUM | Study
COMBUSTION AND FLAME | Study
CONSERVATION OF PLANTS AND ANIMALS | Study
REPRODUCTION IN ANIMALS | Study
REACHING THE AGE OF ADOLESCENCE | Study
FORCE AND PRESSURE | Study
FRICTION | Study
SOUND | Study
CHEMICAL EFFECTS OF ELECTRIC CURRENT | Study

Motion and Time | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Motion and Time | Speed Notes
Notes For Quick Recap
Motion: The action or process of moving or being moved.
The distance moved by an object in a unit time is called its speed.
Speed of objects help us to decide which one is moving faster than the other.
The speed of an object is the distance travelled divided by the time taken to cover that distance.
Its basic unit is mere per second (m/s). (Scroll down to continue …).
Study Tools
Audio, Visual & Digital Content
Periodic events are used for the measurement of time.
Periodic motion of a pendulum has been used to make clocks and watches.
Motion of objects can be presented in pictorial form by their distance-time graphs.
The distance-time graph for the motion of an object moving with a constant speed is a straight line.
Uniform Motion ANd Non – Uniform Motion:
Uniform motion: An object moving with a constant speed is said to be in uniform motion. The average speed is the same as the actual speed.
Non-Uniform motion: If the speed of a moving object keeps changing, the object is said to be in non-uniform motion.
Speed: It is the distance covered by an object in a unit time.
Speed = Total distance/ Total Time
Basic unit of speed is m/s.
Distance-Time Graph: Motion of objects can be presented in pictorial form by their distance-time graphs.
The distance-time graph for the motion of an object moving with a constant speed is a straight line.
Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 7 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023
Electric Current and its Effects | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Electric Current | Speed Notes
Notes For Quick Recap
Flow of electrons through a conductor.
It is convenient to represent electric components by symbols.
Using these, an electric circuit can be represented by a circuit diagram.
When an electric current flows through a wire, the wire gets heated.
It is the heating effect of current. This effect has many applications. (Scroll down to continue …)
Study Tools
Audio, Visual & Digital Content
Wires made from some special materials melt quickly and break when large electric currents are passed through them.
These materials are used for making electric fuses which prevent fires and damage to electric appliances.
When an electric current flows through a wire, it behaves like a magnet.
Electric Circuit: A complete pathway of the flow of electric current.
Component of Electric Circuit: Component of electric circuit are following :
Cell: Provides energy for the current to flow.
Bulb: Lights ups when an electric current flows through it.
Switch: Keeps the circuit off or on.
Connecting wires: Help to conduct the electric current and complete the circuit.
1.Heating Effect: The wire gets hot when an electric current passes through it.
This is the heating effect of the electric current.
Electric heater contains a coil of wire called element which becomes red hot when current passes through it.
The amount of heat produced in a wire depends on its material, length and thickness.
Fuse: It is a safety device which prevents damage to electric circuit.
It is made by inserting a short wire into porcelain or insulating material.
MCB: Stands for Miniature Circuit Breakers. These are switches which automatically turn off when current in a circuit exceeds the safe limit.
Effects of Electric Current:
Electric Current and its Effects
2. Magnetic Effect: When electric current passes through a wire, it behaves like a magnet. This is the magnetic effect of the electric current. This was first observed by Hans Christian Oersted.
A current carrying coil of an insulated wire wrapped around a piece of iron is called an electromagnet.
Electromagnet: An electromagnet is a coil of wire wound on a soft iron core, used to separate magnetic material from the junk. Doctors use tiny electromagnets to take out small pieces of magnetic material that have accidentally fallen in the eye.
Many toys also have electromagnets inside them.

Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 7 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023
Light | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Light | Speed Notes
Notes For Quick Recap
Light: It is the natural agent that stimulates sight and makes things visible.
Light travels along straight line.
Any polished or a shining surface acts as a mirror.
An image which can be obtained on a screen is called a real image. (Scroll down to continue …).
Study Tools
Audio, Visual & Digital Content
It is formed by light rays that actually pass through the screen.
An image which cannot be obtained on a screen is called a virtual image.
It is formed by light rays that seem to pass through the screen.
The image formed by a plane mirror is erect.
It is virtual and is of the same size as the object.
The image is at the same distance behind the mirror as the object is in front of it.
In an image formed by a mirror, the left side of the object is seen on the right side in the image, and right side of the object appears to be on the left side in the image.
A concave mirror can form a real and inverted image.
When the object is placed very close to the mirror, the image formed is virtual, erect and magnified.
A Convex mirror is the mirror that curves out; the reflecting surface is convex.
Image formed is virtual, upright and diminished. Image formed by a convex mirror is erect, virtual and smaller in size than the object.
A Concave lens is the lens that is thinner at the center than at the edges.
It is a diverging lens.
Image formed is virtual, erect and diminished.
A convex lens can form real and inverted image.
When the object is placed very close to the lens, the image formed is virtual, erect and magnified.
When used to see objects magnified, the convex lens is called a magnifying glass.
White light is composed of seven colors.
Properties of Light:
1. Rectilinear Propagation of Light: It is the property of light by which it travels in a straight line in any direction.
The direction of path in which light make a ray.
2. Reflection of Light: It is the bouncing back of light after striking the surface of an object.
Shiny smooth surfaces reflect almost all the light.
3. Dispersion: It is the phenomenon of splitting of white light into its seven colors. White
light is mixture of: Violet, Indigo, Blue, Green, Yellow, Orange and Red (VIBGYOR) colors.

Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 7 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023
Forests: Our Lifeline | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Forests: Our Lifeline | Speed Notes
Notes For Quick Recap
Forest: Large area of land thickly covered with trees, bushes, etc.
We get various products from the forests around us.
Forest is a system comprising various plants, animals and micro-organisms.
In a forest, trees from the uppermost layer, followed by shrubs, the herbs to
the lowest layer of vegetation. (Scroll down to continue …).
Study Tools
Audio, Visual & Digital Content
Different layers of vegetation provide food and shelter for animals, birds and insects.
The various components of the forest are interdependent on one another.
The forest keeps on growing and changing, and can regenerate.
In the forest, there is interaction between soil, water, air and living organisms.
Forests protect the soil from erosion.
Soil helps forests to grow and regenerate.
Deforestation: Cutting down of trees is known as deforestation.
Importance of Forests:

Forests:
Provide timber,
Purify air,
Provide shelter,
Prevent soil,
Absorbs noise.
Independence of Plants and Animals in Forest:
Plants and animals depends on each other to remain alive.
All organisms interact with each other and their physical environment to derive and survive.
Effects of deforestation:
Amount of carbon dioxide in air will increase, resulting in the increase of earth’s temperature. (Global Warming) Animals will not get food and shelter.
Soil will not hold water, which will cause floods.
Endanger lives and environment.
Conservation of Forests:
Do not allow overgrazing.
Promote afforestation.
Protect wildlife.
Food Chain:
Interdependence between producers and consumers studied in form of various linkage that appears as a chain or Interdependence of
organisms which shows who eats whom.
Food Web: A system of interdependent food chains used to represent various relationships in organisms.

Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 7 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023
Wastewater Story | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Wastewater Story | Speed Notes
Notes For Quick Recap
Wastewater: Black-brown water which is rich in lather , mixed with oil that goes down the drains from skins, showers, toilets, laundries is called wastewater.
sewage: Wastewater is generated in homes, industries, agricultural fields and in other human activities. This is called sewage. (Scroll down to continue …).
Study Tools
Audio, Visual & Digital Content
Sewage is a liquid waste which causes water and soil pollution.
Wastewater is treated in a sewage treatment plant.
Treatment plants reduce pollutants in wastewater to a level where nature can take care of it.
Where underground sewerage systems and refuse disposal systems are not available, the low cost on-site sanitation system can be adopted.
By-products of wastewater treatment are sludge and bio gas.
Open drain system is a breeding place for flies, mosquitoes and organisms which cause diseases.
We should not defecate in the open. It is possible to have safe disposal of excreta by low cost methods.
Sewage Treatment:
Aeration: Air is bubbled through the wastewater while it is continuously stirred.
Filtration: Aerated water passes through a deep filter of layered sand, fine gravel and medium gravel.
Chlorination: Chlorine is added and mixed to the filtered water until water is clear.
Wastewater Treatment Plant (WWTP):
Wastewater passes through screens to remove large objects.
To go to a grit and sand removal tank at low speed.
Water is allowed to settle in large tank.
Floating solids are removed with skimmer.
Settled solids (sludge) are removed with scraper.
Clear water is called clarified water.
Water is then decomposed by anaerobic bacteria in a tank and air is passed.
Microbes settled at bottom as activated sludge and water from top is removed.

Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 7 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023
Heat | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Heat | Speed Notes
Notes For Quick Recap
Heat: It is a form of energy, which makes any object hot or cold.
The materials which allow heat to pass through them easily are conductors of heat.
The materials which do not allow heat to pass through them easily are called insulators.
Temperature: The degree of hotness of an object is called temperature.
Heat is the cause of temperature.
Our sense of touch is not reliable to measure the temperature. (Scroll down to continue …)
Study Tools
Audio, Visual & Digital Content
Heat:
It is a form of energy, which makes any object hot or cold.
Temperature: The degree of hotness of an object is called temperature. Our sense of touch is not reliable to measure the temperature.
Thermometer is a device used for measuring temperatures.
Heat is the cause of temperature.
Clinical thermometer is used to measure our body temperature.
Transfer of Heat: Heat flows from a hotter object to a colder object until both objects reach the same temperature.
The heat flows from a body at a higher temperature to a body at a lower temperature.
There are three ways in which heat can flow from one object to another.
These are conduction, convection and radiation.
Conduction: It is the process by which heat is transferred from the hotter end to the colder and end of an object.
Convection: It is the flow of heat through a fluid from places of higher temperature to places of lower temperature by movement of the fluid itself.
Radiation: It is the mode of transfer of heat in which energy is directly transferred from one place to another.
It does not need any material medium.
Dark-coloured objects absorb radiation better than the light-coloured objects.
That is the reason we feel more comfortable in light-coloured clothes in the summer.
Woollen clothes keep us warm during winter.
It is so because wool is a poor conductor of heat and it has air trapped in between the fibres.
Thermometer:
Thermometer is a device used for measuring temperatures.
Clinical thermometer:
Clinical thermometer is used to measure our body temperature.
A thermometer used to measure the temperature of our body is called a clinical thermometer.
For other purposes, we use the laboratory thermometers.
The range of these thermometers is usually from –10°C to 110°C.
The normal temperature of the human body is 37°C.
It consists of a long, narrow, uniform glass tube with a bulb containing mercury at one end.
There is a kink near the bulb.
The range of clinical thermometer is from 35°C to 42°C. (Or from 94°F to 108°F).
Laboratory Thermometer:
Laboratory Thermometer: It is a thermometer used to measure the temperature of objects other than our body.
It consists of a column of mercury enclosed in a glass casing.
The column is continuous without any kink.
It measures a range of temperature from -10˚C to 110˚C.
Sea Breeze:
Sea Breeze: Durign the day, the land heats up faster than the sea.
Warm air above the land rises and cold air from sea takes its place.
Warm air from the land moves towards the sea to compele the cycle.
This produces a sea breeze from the sea to the land.
Land Breeze:
Land Breeze: At night the land cools faster than sea.
The warm air above the sea rises.
This warm air is replaced by colder air from the land producing a land breeze.

Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 7 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023
Acids, Bases and Salts | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Acids, Bases and Salts | Speed Notes
Notes For Quick Recap
There are three types of Substances: Acids, Bases and Salts
Acids: Acids are sour in taste. They are corrosive in nature.
A concentrated acid cuts through clothes and eats away the wool.
If it falls on the skin, it can cause burns.
They are good conductors of electricity, as they allow the passage of electric current through them. (Scroll down to continue …)
Study Tools
Audio, Visual & Digital Content
Types of Acids:
(i) Mineral Acids: These are acids prepared from minerals present in the earth’s crust.
(ii) Organic Acids: These are acids produced by plants and animals (except hydrochloric acid).
Weak Acids: These do not dissociate completely in solution.
Examples: tartaric acid, lactic acid.
Strong Acids: These dissociate completely in solution. Example: nitric acid, sulphuric acid.
Neutralization: It is the reaction between an acid and a base which results in formation of salt and water.
Acid + Base ———-> Salt + Water
Example: HCl + NaOH ———-> NaCl + H₂O
Neutralisation in Everyday Life:
Indigestion: Too much acid in stomach causes indigestion. It is neutralized by taking an antacid like milk of magnesia.
Ant sting: When an ant bites, it injects formic acid into the skin. The effect is neutralized by rubbing moist baking soda (sodium hydrogen carbonate) or calamine (containing zinc carbonate).
(iii) Soil treatment: When the soil is too acidic, it is neutralized by treating with
quicklime (calcium oxide) or slaked lime (calcium hydroxide).
Bases: Bases are bitter in taste and soapy to touch.
Types of Bases:
Weak Bases: These naturally produce less hydroxide ions in solution. Example: magnesium hydroxide, ammonium hydroxide.
Strong Bases: These produce more number of hydroxide ions on dissolving in water. Example: Sodium hydroxide(NaOH), Potassium hydroxide (KOH)
Substances which are neither acidic nor basic are called neutral.
An acid and a base neutralise each other and form a salt. A salt may be acidic, basic or neutral in nature.
Solutions of substances that show different colour in acidic, basic and neutral solutions are called indicators.
Indicators: It is special chemical that changes its colour to indicate the presence of a chemical substance.
It is used to confirm the presence of an acid, a base or a neutral solution.
Classification of Indicators:
Natural Indicators:
Litmus: It is extracted from lichens. It is available in the form of strips of paper or in the form of a solution.· Acid turns blue litmus red. Bases turn red litmus blue.
Turmeric: It remains yellow in neutral and acidic solutions but turns red in alkaline solutions.
China rose: It turns acidic solutions to dark pink (magenta) and basic solution to green.
Red cabbage: It turns acidic solutions to red and basic solutions to blue.
Other Indicators:
Methyl Orange: It gives pinkish red colour with acidic solutions and yellow colour with bases.
Phenolphthalein: It is an acid-base indicator. It is colourless in acidic solutions but turns pink in alkali solutions.
Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 7 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023
Physical and Chemical Changes | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Physical And Chemical Changes | Speed Notes
Notes For Quick Recap
Changes can be of two types, physical and chemical.
Physical changes are changes in the physical properties of substances.
Due to physical chages new substances are not formed.
Physical changes may be reversible.
Examples: crushing a can, glowing of an electric bulb, tearing of paper, mixing of sand and water. (Scroll down to continue …)
Study Tools
Audio, Visual & Digital Content
Chemical Changes are changes in which the composition and chemical properties of the substance get changed.
In chemical changes new substances are produced. The most of the chemical changes are irreversible and permanent.
Note: Some chemical changes are reversible, known as reversible chemical changes.
Example: burning of a candle, formation of curd from milk, ripening of fruits.
Some Chemical Reactions in daily life:
Rusting of Iron: Rusting is the process in which iron turns into iron oxide.
It happens when iron comes into contact with water and oxygen. The process is a type of corrosion that occurs easily under natural conditions.
Prevention of Rusting:
By Painting
By Oiling and greasing
By Chromium plating
By Galvanizing
By Alloying
Cooking of food: Cooking causes breakdown of complex molecules of carbohydrates, fats and proteins into smaller molecules.
It is regarded as a decomposition reaction.
Cooked food is easier to digest than uncooked food.
3. Decay of Organic Substances: Microorganisms like fungi and bacteria produce enzymes which break down complex organic compounds into smaller substances.
It is also regarded as a decomposition reaction.
Some substances can be obtained in pure state from their solutions by crystallization.
Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 7 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023
Respiration in Organisms | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Respiration in Organisms | Speed Notes
Notes For Quick Recap
Respiration is essential for survival of living organisms.
It releases energy from the food.
The oxygen we inhale is used to breakdown glucose into carbon dioxide and water.
Energy is released in this process.
The breakdown of glucose occurs in the cells of an organism (cellular respiration). (ScrollScroll down to continue…)
Study Tools
Audio, Visual & Digital Content
During heavy exercise when the supply of oxygen to our muscle cells is insufficient, food breakdown is by anaerobic respiration (without oxygen)
Types of Respiration:
External respiration also known as breathing refers to a process of inhaling oxygen from the air into the lungs and expelling carbon dioxide from the lungs to the air.
Exchange of gases both in and out of the blood occurs simultaneously.
Internal Respiration: Process in which food is broken down in body cells.
Internal respiration is further classified into two types as aerobic respiration and anaerobic respiration
(a) Aerobic Respiration: Aerobic respiration takes place in the presence of oxygen. Carbon dioxide and water are the end products of aerobic respiration. respiration happens in most of the organisms.
(b) Anaerobic Respiration: Anaerobic respiration takes place in the absence of oxygen.
Anaerobic respiration usually happens in most of the microbes.
Alcohol and carbon dioxide are formed at the end of anaerobic respiration.
In some cases, lactic acid is formed at the end of anaerobic respiration.
Respiration in Plants: Leaves have pores called stomata for gaseous exchange by diffusion.
Stems have openings called lenticels for gaseous exchange by diffusion.
Roots have stomatal pores for gaseous exchange of oxygen dissolved in soil water.
Respiration in Animals: Respiration in animals vary according to their character like:
Earthworm: Earthworms respire through their skin.
Insect: Insects respire through entire body surface.
Fish: Fishes respire through their gills.
Frogs: Frogs respire through their thin, moist and smooth skin when in water and by lungs when on the land.
Respiration in Humans: Inhaled air passes through nostrils into nasal cavity and then into lungs through windpipe.
Breathing is a part of the process of respiration during which an organism takes in the oxygen-rich air and gives out air rich in carbon dioxide.
The respiratory organs for the exchange of gases vary in different organisms.
During inhalation, our lungs expand and then come back to the original state as the air moves out during exhalation.
Increased physical activity enhances the rate of breathing.
In animals like cow, buffalo, dog and cat the respiratory organs and the process of breathing are similar to those in humans.

Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 7 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023
Transportation in Animals and Plants | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Transportation in Animals and Plants | Speed Notes
Notes For Quick Recap
Transportation in animals:
In most of the animals the blood that circulates in the body distributes food and oxygen to different cells of the body.
It also carries waste products from different parts of the body for excretion.
Circulatory system consists of the heart and blood vessels.
In humans, blood flows through arteries and veins and the heart acts as a pumping organ. (Scroll down to continue …)
Study Tools
Audio, Visual & Digital Content
Blood is the fluid which flows in blood vessels.
It transport substance like digested food from the small intestine to the other parts of the body.
Blood consists of plasma, RBC, WBC and platelets.
Blood is red due to the presence of a red pigment, haemoglobin which binds with oxygen and transport oxygen to various parts.
Heart rate:The human heart beats about 70 to 80 times per minute in an adult person. This is called heart rate.
Arteries carry blood from the heart to all parts of the body.
Veins carry blood from all parts of the body back to the heart.
excretion: Removal of waste products from the body is called excretion.
Excretory system of humans consists of two kidneys, two ureters, a urinary bladder, and urethra.
Salts and urea are removed along with water as sweat.
Fish excrete waste substances such as ammonia which directly dissolve in water.
Birds, insects and lizard excrete uric acid in semi-solid form.
Transportation in plants :
Water and mineral nutrients are absorbed by roots from the soil.
xylem: Nutrients are transported along with water to the entire plant via the vascular tissue called xylem.
phloem: The vascular tissue for the transport of food to the various parts of the plant is phloem.
A lot of water is lost by plants in the form of vapour through stomata during transpiration.
Transpiration generates a force which pulls up water absorbed by the roots from the soil, to reach the stem and leaves.

Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 7 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023
Reproduction in Plants | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Reproduction in Plants | Speed Notes
Notes For Quick Recap
All organisms multiply or reproduce offspring of their own kind.
In plants there are two modes of reproduction, namely (a) Asexual reproduction and (b) Sexual reproduction.
There are several methods of asexual reproduction such as fragmentation, budding, spore formation and vegetative propagation.
Sexual reproduction involves the fusion of male and female gametes. (Scroll down to continue …)
Study Tools
Audio, Visual & Digital Content
In vegetative propagation new plants are produced from different vegetative parts such as leaves, stems and roots.
Flower is the reproductive part of a plant.
A flower may be unisexual with either the male or the female reproductive parts.
A bisexual flower has both the male and the female reproductive parts.
The male gametes are found inside the pollen grains and female gametes are found in the ovule.
Pollination is the process of transfer of pollen grains from the anther of one flower to the stigma of the same or another flower.
Pollination is of two types, self-pollination and cross-pollination.
In self-pollination, pollen grains are transferred from the anther to the stigma of the same flower.
In cross-pollination, pollen grains are transferred from the anther of one flower to the stigma of another flower of the same kind.
Pollination takes place in plants with the help of wind, water and insects.
The fusion of male and female gametes is called fertilization.
Fertilized egg is called zygote.
Zygote develops into an embryo.
Fruit is the mature ovary whereas ovule develops into a seed, which contains the developing embryo.
Seed dispersal is aided by wind, water and animals.
Seed dispersal helps the plants to:
prevent overcrowding,
avoid competition for sunlight, water and minerals
invade new habitats.
Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 7 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023
CBSE 7 | Science – Study – Free
Educational Tools | Full Course
Study Tools
Audio, Visual & Digital Content
[display-posts category=”CBSE 7 – Science – Study – Premium” posts_per_page=”25″]
Assessment Tools
Assign, Assess & Analyse
[display-posts category=”CBSE 7 – Science – Assess – Premium” posts_per_page=”25″]
Connnect With Us
Enrich our growing community
November 5, 2023
Nutrition in Plants | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Speed Notes
Notes For Quick Recap
Nutrition: It is the mode of taking food by an organism and its utilization by the body.
Nutrients: The components of food that provide nourishment to the body.
All organisms take food and utilise it to get energy for the growth and maintenance of their bodies. (Scroll down to continue …)
Study Tools
Audio, Visual & Digital Content
Autotrophs: Autotrophs are the green plants which synthesise their food themselves by the process of photosynthesis.
Photosynthesis: the process of preparation of own food by the Green plants with the help of chlorophyll (found in green plants), carbon dioxide and water taken from the environment in presence of sunlight is known as photosynthesis.
Plants use simple chemical substances like carbon dioxide, water and minerals for the synthesis of food.
Chlorophyll and sunlight are the essential requirements for photosynthesis.
Complex chemical substances such as carbohydrates are the products of photosynthesis.
Solar energy is stored in the form of food in the leaves with the help of chlorophyll.
Oxygen is produced during photosynthesis.
Oxygen released in photosynthesis is utilised by living organisms for their survival.
Fungi derive nutrition from dead, decaying matter.
They are saprotrophs.
Plants like Cuscuta are parasites.
They take food from the host plant.
A few plants and all animals are dependent on others for their nutrition and are called heterotrophs.
Parasitic: Organisms that live on the body of other organisms. All parasitic plants feed on other plants as either:
Partial Parasites: Obtain some of their nutrition from the host,
Example: Painted cup
Total Parasites: Dependent completely on the host for nutrition.
Example: Mistletoe.
Nutrition in plants
Saprophytic: Organisms that obtain nutrition from dead and decaying plant and animal matter.
Mushrooms, moulds and certain types of fungi and bacteria.
Insectivorous Plants: Green plants which obtain their nourishment partly from soil and atmosphere and partly from small insects.
Example: pitcher plant, bladderwort, and venus fly trap.
Symbiosis: Mode of nutrition in which two different individuals associate with each other to fulfil their requirement of food.
Lichens found on tree trunks is the association between algae and fungus.
Algae obtains water from fungus and it in turn obtains food from algae.

Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 7 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023
Nutrition in Animals | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Nutrition in Animals | Speed Notes
Notes For Quick Recap
Classification based on Eating Habits:
Herbivorous: Animals that eat plants or plant products.
Example: Cow, sheep, goat, deer, elephant, kangaroo, giraffe, etc.
Carnivorous: Animals that eat only flesh of other animals. They never eat plants.
Examples: Tiger, lizard, lion, etc.
Omnivorous: Animals consume plants as well as other animals as their food.
Examples: Bear, dog, human being, etc.
Parasites: Organisms that obtain their food from other animals either by living inside (endoparasites) or outside (ectoparasites) their body.
Examples: Tapeworm and roundworm (inside body), tick and lice (outside body).
Scavengers: Animals which feed on the remains of dead animals preyed by predators. Example: vulture, crows, jackal, etc. (Scroll down to continue …)
Study Tools
Audio, Visual & Digital Content
The main digestive glands which secrete digestive juices are:
the salivary glands,
the liver and
(iii) the pancreas.
The human digestive system consists of the alimentary canal and secretory glands.
It consists of:
buccal cavity,
oesophagus,
stomach,
small intestine,
large intestine ending in rectum
anus.
Animal nutrition includes nutrient requirement, mode of intake of food and its utilisation in the body.
The stomach wall and the wall of the small intestine also secrete digestive juices.
The modes of feeding vary in different organisms.
Nutrition is a complex process involving:
ingestion,
digestion,
absorption,
assimilation and
egestion.
Digestion of carbohydrates, like starch, begins in the buccal cavity.
The digestion of protein starts in the stomach.
Bile secreted from the liver, the pancreatic juice from the pancreas and the digestive juice from the intestinal wall complete the digestion of all components of food in the small intestine.
The digested food is absorbed in the blood vessels from the small intestine.
The absorbed substances are transported to different parts of the body.
Water and some salts are absorbed from the undigested food in the large intestine.
The undigested and unabsorbed residues are expelled out of the body as faeces through the anus.
The grazing animals like cows, buffaloes and deer are known as ruminants.
They quickly ingest, swallow their leafy food and store it in the rumen.
Later, the food returns to the mouth and the animal chews it peacefully.
Amoeba ingests its food with the help of its false feet or pseudopodia.
The food is digested in the food vacuole.
It pushes out finger-like pseudopodia which engulf the prey.
Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 7 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023
LIGHT | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Speed Notes
Notes For Quick Recap
Light
Light is the natural agent that stimulates sight and makes things visible. Light is reflected from all surfaces. It is a form of energy.
Reflection of Light: Bouncing back of light after striking any surface such as a rough surface, Smooth surfce, shiny surface or polished surface, into the same medium, is called reflection of light. (Scroll down to continue …)
Study Tools
Audio, Visual & Digital Content
luminous objects: Objects that give out light on their own are called luminous objects.
Examples: Flame, Sun, Glowing bulb
Non-luminous objects: Objects that do not give out light on their own are called non-luminous objects.
Examples: Rocks, Plasic Toys, Walls of room.
The Non – Luuminous objects, reflect light that falls on them.
When the reflected light enters into our eyes from the objects we could see them.
Types of Reflection:
(i) Regular Reflection: When a beam of parallel light rays is incident on a smooth and plane surface, the reflected rays will also be parallel. This type of reflection is called Regular Reflection.
The reflection from a plane mirror is an example of regular reflection.
(ii) Diffused or Irregular Reflection: When a parallel beam of light is incident upon a rough or uneven surface, it is reflected in many directions due to presence of irregularities on that.
multiple reflections: If a reflected light ray is reflected again on being incident on another surface, it is termed as multiple reflections.
Multiple reflections are used in periscope, kaleidoscope etc.
Periscopes are used in submarines, war tanks and by soldiers in bunkers to see objects.
In a kaleidoscope, beautiful patterns are formed due to multiple reflections.
Laws of reflection of light:
(i) The angle of incidence is equal to the angle of reflection.
(ii) Incident ray, reflected ray and the normal drawn at the point of incidence to the reflecting surface, lie in the same plane.
Lateral inversion: Lateral inversion is the effect produced by a plane mirror in reversing images from left to right.
Example: Our left hand will appear as right and vice versa.
Characteristics of the image formed by a plane mirror
Size the image formed by a plane mirror is equal to the siz of the object.
The image formed by the plane mirror is left-right inverted.
The image formed by the plane mirror erect and virtual formed behind the mirror.
Since the distance of the object in front of the mirror two mirrors inclined to each other give multiple images.
Sunlight: Sunlight, called white light, consists of seven colours.
dispersion: Splitting of light into its constituent colours is known as dispersion.
Human Eye:
A normal eye can see nearby and distant objects clearly.
Visually challenged persons can read and write using Braille system.
Visually challenged persons develop their other senses more sharply to improve their interaction with their environment.
Parts of Human Eye:
(i) Cornea: Transparent bulge on the front surface of the eyeball which protects the eye andhelps in refraction of light.
(ii) Iris: Coloured diaphragm behind the cornea which controls the amount of light
entering the eye.
(iii) Pupil: Dark hole in the middle of iris through which light enters the eye. (iv) Eye lens: Transparent, crystalline structure behind pupil and iris. (v) Ciliary muscles: Hole the eye lens in position and control the focal length of the eye lens.
(vi) Retina: Surface of the rear part of the eyeball where the light entering the eye is focused.
(vii) Rods and Cones: Rod cells respond to the brightness of light while cone cells.

Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 8 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023
COAL AND PETROLEUM | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Speed Notes
Notes For Quick Recap
Natural Resources: Resources include everything provide by the nature. They form the wealth of a country.
Types of Natural Resources:
(i) Inexhaustible: There are some resources that are present unlimited in nature and will not be exhausted even if used continuously.
Example: Sunlight, Air. (Scroll down to continue …)
Study Tools
Audio, Visual & Digital Content
(ii) Exhaustible: These resources are limited and can soon get exhausted because of Coal, petroleum and natural gas are fossil fuels.
Fossil fuels were formed from the dead remains of living organisms millions of yearsago.
Fossil fuels are exhaustible resources.
Coke, coal tar and coal gas are the products of coal.
Petroleum gas, petrol, diesel, kerosene, paraffin wax, lubricating oil are
obtained by refining petroleum.
Coal and petroleum resources are limited.
We should use them judiciously.
Petroleum is mixture of various constituents such as petroleum gas, petrol, diesel, lubricating oil, paraffin wax, etc.
Refining: Refining is the process of refracting the various constituents / fractions of petroleum.
It carried out in a petroleum refinery.
Natural Gas: A very important fuel as it easy to transport through pipes and can be compressed and stored under high pressure as Compressed Natural Gas (CNG).
It causes no pollution and has high calorific value.

Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 8 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023
COMBUSTION AND FLAME | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Speed Notes
Notes For Quick Recap
Combustion and Flame
Combustion: The process of burning a substance in the presence of air (oxygen) andundergoes a chemical reaction to produce heat and light. The substances which burn in air are called combustible.
Oxygen (in air) is essential for combustion. During the process of combustion, heat and light are given out. Ignition temperature is the lowest temperature at which a combustible substancecatches fire.
Types of combustion: The type of combustion differs depending on the type of fuel. (Scroll down to continue)
Study Tools
Audio, Visual & Digital Content
Based on nature and intensity combustions are classified into three types. They are:
(i) Rapid combustion
(ii) Spontaneous combustion
(iii) Explosion
Flame: It is a zone or burning vapour. The substances which vaporise during
burning give flames.
Example: Kerosene oil and molten wax. Inflammable substances have very low ignition temperature. Fire can be controlled by removing one or more requirements essential for producing fire. Water is commonly used to control fires. Water cannot be used to control fires involving electrical equipments or oils.
There are three different zones of a flame – dark zone, luminous zone and non-luminous zone.
Fuel is any material that is burned to obtain energy that can be used to heat or
A good fuel must:
Be readily
available. Be cheap. Burn easily at a moderate rate.
Produce a large amount of heat. • Not leave behind any undesirable
Fuels differ in their efficiency and cost. Fuel efficiency is expressed in terms of its calorific value which is expressed in
units of kilo joule per kg.
Types of Fuels:
(i) Solid Fuels: Combustible substances which are solid at room
temperature.Example: coal, coke, wood, charcoal, etc. (ii) Liquid fuels: Volatile liquids which produce combustible vapour. Example:
Petrol,kerosene, alcohol, diesel, etc. (iii) Gaseous fuels: Combustible gases or mixture of combustible gases. Example:
Effects of Burning of Fuels:
(i) Carbon fuels like wood, coal petroleum release un burnt carbon particles. Theseare dangerous pollutants causing respiratory diseases, such as asthma.
(ii) Incomplete combustion of carbon fuels gives carbon monoxide which
is apoisonous gas.
(iii) Increased concentration of carbon dioxide in the air is believed to cause
globalwarming.
(iv) Oxides of Sulphur and nitrogen dissolve in rain water and form acids. Such
rain is Un burnt carbon particles in air are dangerous pollutants causing respiratoryproblems.
Incomplete combustion of a fuel gives poisonous carbon monoxide gas. Increased percentage of carbon dioxide in air has been linked to global warming.
Oxides of sulphur and nitrogen produced by the burning of coal, diesel and
petrol cause Acid rain which is harmful for crops, buildings and soil.
Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 8 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023
CONSERVATION OF PLANTS AND ANIMALS | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Speed Notes
Notes For Quick Recap
Conservation of Plants and Animals
Biodiversity: Occurrence of innumerable types of organisms and the whole range of their varieties (biotypes) adapted to different climates, environments and areas. Wildlife sanctuary, national park and bio-sphere reserve are names given to the areas meant for conservation and preservation of forest and wild animals. (Scroll down to continue …)
Study Tools
Audio, Visual & Digital Content
Biodiversity refers to the variety of living organisms in a specific area.
Plants and animals of a particular area are known as the flora and fauna of that area.
Endemic species are found only in a particular area.
Endangered species are those which are facing the danger of extinction.
Red Data Book contains a record of endangered species.
Migration is the phenomenon of movement of a species from its own habitat to some other habitat for a particular time period every year for a specific purpose like breeding.
We should save, reuse and recycle paper to save trees, energy and water.
Reforestation is the restocking of destroyed forests by planting new trees.
Flora: Different types of plants belonging to an area.
Example: Silver ferns, sal, teak, mango, etc.
Fauna: All animals found in an area.
Example: dog, frog, insects, bull, jackal, etc.
Endemic Species: Species of plants and animals found exclusively in a particular area.
These are not naturally found anywhere else.
Extinct Species: Species of plants and animals which have already been lost.
Type of Threatened Species:
(ii) Vulnerable Species: A vulnerable species is a species of animals or plants which are likely to become endangered unless something changes.
Example: Chinkara deerand black buck, golden langur, etc
(iii) Rare Species: Species whose population are originally small and scattered in the National Parks: Protective areas reserved exclusively for the betterment of the wildlife. These are established at the approval of legislature.
Example: Hazaribagh National Park in Jharkhand, Desert National Park in Rajasthan.
Sanctuaries: Hunting prohibited areas set up by government are known as sanctuaries. These are only for the protection of wild animals.
Example: Jaldapara in Madarihat (West Bengal), Keoladeo Ghana in Bharatpur (Rajasthan)
igration: The regular, periodic, two way movements of birds and some animals from their place of residence to some other place along well defined routes. It is linked to seasonal factors, breeding, shortage of foods, etc.
The sanctuary is known for the migratory birds.

Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 8 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023
REPRODUCTION IN ANIMALS | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Speed Notes
Notes For Quick Recap
Reproduction in Animals
Reproduction is a process in which the organisms produce the young ones of their own kind. There are two modes by which animals reproduce.
These are: (i) Sexual reproduction, and (ii) Asexual reproduction (Scrolldown to continue …)
Study Tools
Audio, Visual & Digital Content
Sexual Reproduction
Reproduction resulting from the fusion of male and female gametes is called sexual reproduction.
The reproductive organs in the female include ovaries, oviducts and uterus.
The reproductive organs in male include testes, sperm ducts and penis.
The ovary produces female gametes called ovum and the testes produce male gametes called sperms. The fusion of ovum and sperm is called fertilization.
zygote: The fertilized egg is called a zygote.
internal fertilization: Fertilization that takes place inside the female body is called internal fertilization. This is observed in human beings and other animals such as hens, cows and dogs.
external fertilization: Fertilization that takes place outside the female body is called external fertilization. This is observed in frogs, fish, starfish, etc.
The zygote divides repeatedly to give rise to an embryo. The embryo gets embedded in the wall of the uterus for further development.
The stage of the embryo in which all the body parts are identifiable is called foetus.
Animals such as human beings, cows and dogs which give birth to young Ones.
Asexual Reproduction: The type of reproduction in which only a single parent is involved is called asexual reproduction. The transformation of the larva into adult through drastic changes is called Asexual Reproduction
budding: In hydra, new individuals develop from buds. This method of asexual reproduction is called budding.
binary fission.: Amoeba reproduces by dividing itself into two. This type of asexual reproduction is called binary fission.

Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 8 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023
REACHING THE AGE OF ADOLESCENCE | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Speed Notes
Notes For Quick Recap
Reaching The Age of Adolescence
Humans become capable of reproduction after puberty. Puberty sets in between the ages of 11 years and 19 years. These children are called adolescents.
The onset of puberty brings about growth of the reproductive organs. Hairs grow at various places on the body.
Breasts develop in girls.
Facial hair (moustache and beard) appear in boys.
Voice of boys become hoarse as voice box enlarges during adolescence.
Children gain height during adolescence.
Puberty: It is the time when sex organs begin to work.
It brings about growth in reproductive organs and changes in the body.
Puberty starts at the beginning of adolescence.
Study Tools
Audio, Visual & Digital Content
Reaching the age of Adolescence
The onset of puberty starts much earlier in girls, between 8 and 13 years of age, whereas it starts between 10 and 14 years of
age in boys and lasts upto 2 to 4 years.
Changes during Puberty:
(i) Increase in Height: The bones of the legs and arms elongate and the individual becomes tall and lanky.
(ii) Changes in Body Shape: In boys, the body becomes more muscular, the shoulder becomes wider.
In girls, the body shows curves in certain parts and the region below the waist become wider and broader.
(iii) Change in Voice: In boys, the voice becomes hoarse and heavy due to the extra growth of larynx (voice box).
In girls, the voice becomes high pitched and shriller.
(iv) Sweat and sebaceous glands: They become more active and secrete more.
(v) Emotional aspects develop.
Periodic cycle of 28 days. The onset of puberty and maturity of reproductive parts are controlled by hormones.
Hormones are secretions of endocrine glands which pour them directly into the blood stream.
Pituitary gland secretes hormones which include growth hormone and hormones that make other glands such as the testes, ovaries, thyroids and adrenals, secrete hormones.
Pancreas secretes insulin, thyroid produces thyroxin and adrenals produce adrenalin.
Testosterone is the male hormone and estrogens, the female hormone.
The uterine wall in females prepares itself to receive the developing fertilised egg.
Menstruation: In case there isno fertilisation, the thickened lining of the uterine wall breaks down and goes out of the body along with blood.This is called menstruation.
Sperm and Ovum fuses together to form a zygote.
Sex chromosomes in sperms determine the baby’s gender. Humans have 23 pairs of chromosomes in each cell.
A pair of chromosome forms the sex chromosomes. Males carry XY and females carry XX chromosomes.
If a sperm carrying X fertilises the ovum with X chromosome, then the resulting baby is a girl.
If a sperm carrying Y chromosome fertilises the ovum with X chromosome, then the resulting baby is a boy.
Hence, males are responsible for the gender of the newly formed babies, Not Women.
Reproductive Health:
It is important to eat balanced food and maintain personal hygiene during adolescence.
Cleaning of private parts is important to prevent possible infections.
The activity of sweat glands increases in puberty and releases bad odour from the body.
Thus frequent bathing is necessary. Physical exercise keeps the body fit and healthy as it releases lot of sweat.
Peer pressure is best addressed by self-confidence and a healthy lifestyle.

Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 8 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023
FORCE AND PRESSURE | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Speed Notes
Notes For Quick Recap
Force And Pressure
Force: A push or a pull, that changes or tends to change the state of rest or of uniform motion of an object or changes its direction or shape.
A force arises due to the interaction between two objects.
Force has magnitude as well as direction.Therefore force is a vector quantity.
The SI unit of force is newton. (Scroll down to continue …)
Study Tools
Audio, Visual & Digital Content
A change in the speed of an object or the direction of its motion or both implies a change in its state of motion.
Force acting on an object may cause a change in its state of motion or a change in its shape.
Contact Non Contact Forces:
A force can act on an object with or without being in contact with it. Based on Contact the forces are classclassified as Contact Forces and Non Contact Forces.
Contact Forces: The forces act on a body when the source of force touches the body directly.
The point where the force is applied on an object is called the point of application of force (or point of contact).
Examples of Contact Forces:
(i) Muscular Force: The force exerted by the muscles of the body.
We use force acted by muscles of animals like Humans, bullocks, horses and camels to get our activities done.
(ii) Mechanical Force: The force acted by a machine.
Non-Contact Forces:
Non-Contact Forces: Forces which do not involve physical contact between two bodies on which they act.
Examples of Non-Contact Forces:
(i) Magnetic Force: A magnet exerts a non-contact force on objects made of iron, steel, cobalt or nickel.
(ii) Electrostatic Force: The force which result due to repulsion of similar charges or attraction of opposite charges.
(iii) Gravitational Forces: The force that exists between any two bodies by virtue of
Pressure
Pressure: Thrust acting per unit surface area is called pressure.
Thrust
Thrust is the force acting on an object perpendicular to its surface.
In SI system, pressure is measured in newton per square metre which is equal to 1 pascal (Pa).
Like solids, fluids (liquids and gases) also exert pressure.
A solid exerts pressure only in the downward direction due to its weight, whereas liquids and gases exert pressure inall directions.
Hence liquids and gases exert pressure on the walls of their container.
Atmospheric Pressure
Ttmosphere: The thick blanket of air that covers the earth is termed atmosphere.
The pressure exerted by the atmosphere is called atmospheric Pressure.
The tremendous atmospheric pressure surrounding us is not felt by us because the fluid pressure inside our bodies counter-balances the atmospheric pressure around us.

Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 8 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023
FRICTION | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Speed Notes
Notes For Quick Recap
Friction:
Friction is the force that resists the motion of one object against another. It is the force felt between two surfaces when one attempts to slide against the other.
Causes of Friction: Friction exists between two surfaces due to irregularities on the surfaces of the objects in contact, interlocking of micro-level irregularities of the two surfaces and ploughing of harder surfaces into smoother surfaces.
Factors Affecting Friction:
(i) Roughness of the surface.
(ii) The extent to which the two surfaces press against each other.
(iii) Nature of the surface· (Scroll doen to continue …)
Study Tools
Audio, Visual & Digital Content
Types of Friction: Friction is classified into three types as: Static Friction, Sliding Friction, Rolling Friction.
(i) Static Friction: When a body is at rest, the force of friction is called the static friction and is always equal and opposite to the applied force.
limiting friction: The force of friction which acts when the body is just at the verge of sliding on the surface is called limiting friction.
Motion between two contacting surfaces
(ii) Sliding friction: The friction force which opposes the actual relative sliding motion between two contact surfaces.
Sliding friction is smaller than static friction.
(iii) Rolling Friction: The frictional force that exists between two surfaces when a body rolls over the other.
Rolling friction is smaller than sliding friction.
Static friction > Sliding friction > Rolling friction
Effects of Friction
(i) Friction produces heat.
(ii) Friction causes wear and tear.
(iii) Friction opposes motion.
Advantages of Friction
(i) Friction between pen and paper enables us to write on the paper.
(ii) Friction between our feet and the ground allows our movements like standing, walking and running.
(iii) Friction between the surface of the road and tyres of our vehicles allow the vehicles to move without slipping.
Disadvantages of Friction:
(i) Friction causes moving objects to stop or slow down.
(ii) Friction produces heat causing wastage of energy in machines.
(iii) Friction causes wear and tear of moving parts of machinery, soles of shoes, etc.
Friction is a necessary Evil:
As friction is advantageous to us it is considered as a friend but, due to its disadvantages it is a foe.
Depending on the circumstance, friction can be a help or a hindrance.
Thus it is a necessary evil.
Increasing Friction: By pressing the surfaces together more strongly.
For example, when brakes are applied on a bicycle or car, the brake pads press against a moving part of the wheel and the force of friction increases.
Friction can be increased by increasing the roughness of the surfaces in contact.
For example, treading of shoes and tyres is done to increase friction.
Reducing Friction: Friction between the sliding surfaces of two objects can be reduced by making the surfaces in contact smooth by polishing them.
Sliding friction between the moving parts of vehicles and machinery can be reduced by introducing oil, grease, graphite or any other lubricant.
Lubricant: A lubricant is a substance that reduces friction between surfaces in contact. This reduces the heat generated when the surfaces move. Lubricants can also transmit forces, transport foreign particles, or heat or cool the surfaces.
Rolling friction is less than sliding friction. Hence, sliding friction is replaced by rolling friction by using rollers, like ball bearings between the hub and the axles in the moving parts of machines and vehicles.
Friction is reduced by providing wheels,
Examples: suitcase, school bags of kids, etc.
Streamlined shape: Aeroplanes, boats, fishes and birds which move through fluids have bodies of special shape, called streamlined shape, The streamlined shape reduces the friction due to fluid and reduces the energy usage.

Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 8 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023
SOUND | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Speed Notes
Notes For Quick Recap
Sound: Vibrations that travel through the air or another medium and can be heard
when they reach a person’s or animal’s ear. Musical Sound: The sound which produce a pleasing effect on the ear.
Noise: The sounds which produce a jarring or unpleasant effect. (Scroll down to contue …)
Study Tools
Audio, Visual & Digital Content
Types of Sound:
(i) Audible Sound: Vibrations whose frequency lies between 20 Hz to 20,000 Hz (20
kHz) are heard by human ear.
(ii) Inaudible Sound: The sounds having frequencies above 20,000 Hz and below
20 Hz cannot be heard by the normal human ear.
Low frequency sounds which cannot be heard are called infrasonics.
High frequency sounds which cannot be heard are called ultrasonics.
In human beings, the vibration of the vocal cords produces sound.
Sound travels through a medium (gas, liquid or solid). It cannot travel in
vacuum.
The eardrum senses the vibrations of sound. It sends vibrations to the inner ear. From
there, the signal goes to the brain.
That is how we hear. Higher the frequency of vibration, the higher is the pitch, and shriller is the
sound. Unpleasant sounds are called noise.
Excessive or unwanted sounds lead to noise pollution. Noise pollution may pose health problems for human beings. Lack of sleep, hypertension (high bloodpressure), anxiety and many more health disorders may be caused by noise pollution.
A person who is loud sound continuously may get temporary or even permanent impairment of hearing.
Attempts should be made to minimise noise pollution. Silencing devices must be installed in air craft engines, transport vehicles, industrial machines and home appliances. Plantation on the roadside and elsewhere can reduce noise pollution.
Amplitude: The maximum extent of vibration of the vibrating body from its mean position is known as its amplitude.
Time Period: One complete to and fro movement of the pendulum around its mean positionis called one oscillation.
The time taken by the vibrating particle to complete one oscillation is called time period.
Frequency: The number of vibrations made by the vibrating body in one second is known as its frequency. The SI unit of frequency is the hertz (Hz).
Characteristics of Sounds:
(i) Loudness: The sensation produced in the ear which enables us to distinguish between a loud and a faint sound. Larger the amplitude of vibration, the louder is the sound produced. It is proportional to square of the amplitude.
(ii) Pitch: The characteristics of sound which distinguishes between a shrill sound and a soft sound.
Higher the frequency of vibration, higher is the pitch and shrillness.
(iii) Quality: Characteristic which enables us to distinguish between musical notes emittedby different musical instruments or voices even though they have the same.

Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 8 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023
CHEMICAL EFFECTS OF ELECTRIC CURRENT | Study
Assess
Interact
Pre-Requisires
Test & Enrich
Pre – Requisite

English Version
Speed Notes
Notes For Quick Recap
Chemical Effects of Electric Current
Materials through which electric current can pass through easily are called electric conductors or conductors of electricity.
Electrical conductivity Or Electric Conductivity: Electrical conductivity is a measure of the ability of a substance to allow the flow of electric current.
Among solids metals and graphite are good conductors which have high electrical conductivity.
Some liquids are also good conductors.
Study Tools
Audio, Visual & Digital Content
Pure water or distilled water is a poor conductor of electricity. But the presence of even small amount of impurities(salts and minerals) makes water a good conductor as it contains ions through which conduction takes place.
Hence water from taps, wells, lakes, etc. conduct electricity as they contain impurities.
Most liquids that conduct electricity are solutions of acids, bases and salts.
When electricity is passed through a conducting solution, the molecules of the solution dissociate into ions.
Ions are atoms or group of atoms with a positive or a negative charge.
These ions cause electrical conduction through the liquid.
Electrolyte: A liquid That conducts electricity is called an electrolyte.
Electrolysis:
The process of chemical decomposition compound in a solution when an electric current passes through it is called electrolysis.
Electrolysis, is due to the chemical effect of electric current.
electrolytic cell: Two electrodes are inserted in the solution and are connected to the terminals of a battery with a switch in between them.
This arrangement is called an electrolytic cell.
anode: The electrode that is connected to the positive terminal of the battery is called the anode,
cathode: The electrode that is connected to the negative terminal of the battery is called the cathode.
Electrolysis is used in refining, electroplating and extraction of metals from impure samples.
electrorefining: This process of refining and extraction of metals from impure samples is called electrorefining.
electroplating: electroplating is the process of coating a useful metal with another metal.
chemical effect of electric current: The process of passing an electric current through a conducting solution to cause chemical reactions is known as the chemical effect of electric current.
Chemical effects of electric current:
(i) Formation of bubbles of a gas on the electrodes.
(ii) Deposition of metal on electrodes.
(iii) Change in colour of solutions.
Electroplating: The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating. The object to be electroplated is made the cathode (negative electrode) by connecting it to thenegative terminal of the battery.
The metal which has to be deposited is made the anode (positive electrode) by connecting it to the positive terminal of the battery. Usually a salt solution of the metal to be coated is made as anode.
Application of Electroplating:
(i) Metals that rust are often coated with other metals to prevent rusting.
(ii) Chromium plating is found on bath taps, car bumpers, etc. to give a bright attractive appearance and resist scratches and wear.
(iii) Silver plating is done on cutlery and jewellery items.
(iv) Tin cans, used for storing food, are made by electroplating tin onto iron.
Tin is less reactive than iron. Thus, food does not come into contact with iron and is protected from getting spoilt.

Hindi Version
Dig Deep
Topic Level Resources
Sub – Topics
Select A Topic
Topic:
Chapters Index
Select Another Chapter
[display-posts category=”CBSE 8 – Science – Study – Premium” posts_per_page=”25″]
Assessments
Personalised Assessments
Assess
November 5, 2023

error: Content is protected !!

Scan the code

Your cart (items: 0)

Products in cart
Product	Details	Total
	Available on backorder Previous price: Discounted price: Save	Save