Notes For Quick Recap
Some Natural Phenomena
Some objects can be charged by rubbing with other
objects. There are two kinds of charges — positive charge and negative charge Like charges repel and unlike charges attract each other.
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Static Electric Charges: The electric charges produced due to rubbing are called static electric charges. The electric charges constitute electric current during their motion.
An electroscope may be used to detect whether a body is charged or not.
An electroscope is a deviced used to detect the presence of electric charge.
earthing: The process of transfer of charge from a charged object to the earth is called earthing.
Lightning is a sudden, natural and violent phenomenon of creating bright flashes during a thunderstorm.
Lightning occurs due to a high-voltage electric discharge between two clouds or a cloud and the ground, or within a single cloud during a thunderstorm.
The formation of clouds involves friction between water droplets in the atmosphere.
The friction charges the particles in the atmosphere. The negative charges accumulate at the bottom of the cloud and the positive charges at the top.
As the accumulation of the charges increases, the cloud will induce positive charges on the ground nearby.
As the amount of charge increases. This causes an imbalance of charges between a region of a cloud and gorund or another cloud (or in a cloud itself). This imbalance is significant enough to break through air resistance.
Lightning releases an average of one gigajoule of energy.
Lightning strike could destroy life and property.
Protective measures are of utmost importance during lightning strikes.
Taking shelter in interiors (house or other closed places) and vehicles (closed e.g. cars) are the most preferred measures.
Lightning conductors can protect buildings from the effects of lightning.
A natural phenomenon that cannot be predicted is an earthquake.
The earth consists of three major layers, called the crust, the mantle and the core.
The core is further divided into the inner core and the outer core.
The mantle consists of semi-solid material above which the crust floats.
The crust consists of oceans and continents.
The crust is divided into several parts, called tectonic plates.
The regions where one tectonic plate slides against another are referred to as fault zones, and these are the regions where an earthquake is likely to occur.
Hence, these zones are referred to as seismic zones.
The place in the interior of the earth where an earthquake occurs is the focus, and the region on the surface of the earth that is the closest to focus is likely to experience the largest damage.
This region is called the epicenter of the earthquake.
The instrument that measures the severity of an earthquake is a seismograph.
It basically consists of a drum that rolls and a pendulum with a stylus that traces the waves of an earthquake on a sheet like a graph paper.
The energy released at the focus propagates outwardly in form of waves known as seismic waves. Destructive energy of an earthquake is measured on the Richter scale.
It is a logarithmic scale, ranging from 1 to 10 for indicating the intensity of an earthquake.
The earthquake measuring 7 or more on Richter scale can cause severe damage to life and property. Protective measures for earthquake:
If you are at home:
Take shelter under a table and stay there till shaking stops.Stay away from tall and heavy objects that may fall on you. If you are in bed, do not get up. Protect your head with a pillow.
If you are outdoors: Find a clear spot, away from buildings, trees and overhead power lines. Drop to the ground. If you are in a car or a bus, do not come out. Ask the driver to drive slowly to a clear spot. Do not come out till the tremors stop. Moreover, it is advisable to make the structure of buildings simple so that they are ‘Quake Safe’.