Lightning is also an electric spark, but on a huge scale.
When a plastic refill is rubbed with polythene, it acquires a small electric charge. Similarly, when a plastic comb is rubbed with dry hair, it acquires a small charge. These objects are called charged objects. the process of charging the refill and the plastic comb, polythene and hair also get charged.
It is a convention to call the charge acquired by a glass rod when it is rubbed with silk as positive. The other kind of charge is said to be negative.
The electrical charges generated by rubbing are static. They do not move by themselves. When charges move, they constitute an electric current.
The current in a circuit which makes a bulb glow, or the current that makes a wire hot, is nothing but a motion of charges.
The aluminium foil strips receive the same charge from the charged refill through the paper clip. Such a device can be used to test whether an object is carrying charge or not. This device is known as electroscope.
The electrical charge can be transferred from a charged object to another through a metal conductor.
The process of transferring of charge from a charged object to the earth is called earthing.
When the positive charges collect near the upper edges of the clouds and the negative charges accumulate near the lower edges. There is accumulation of positive charges near the ground also. When the magnitude of the accumulated charges becomes very large, the air which is normally a poor conductor of electricity, is no longer able to resist their flow. Negative and positive charges meet, producing streaks of bright light and sound. Then we see the lightning and the process is known as electric discharge.
The process of electric discharge can occur between two or more clouds, or between clouds and the earth.
During lightning and thunderstorm no open place is safe.
Hearing thunder is an alert to rush to a safer place.
After hearing the last thunder, wait for some time before coming out of the safe place.
Finding a Safe Place
A house or a building is a safe place. If we are travelling by car or by bus, we are safe inside with windows and doors of the vehicle shut.
Lightning Conductor is a device used to protect buildings from the effect of lightning. A metallic rod, taller than the building, is installed in the walls of the building during its construction. One end of the rod is kept out in the air and the other is buried deep in the ground. The rod provides easy route for the transfer of electric charge to the ground.
An earthquake is a sudden shaking or trembling of the earth which lasts for a very short time. It is caused by a disturbance deep inside the earth's crust. Earthquakes occur all the time, all over the earth.
Major earthquakes are much less frequent. They can cause immense damage to buildings, bridges, dams and people. There can be a great loss to life and property. Earthquakes can cause floods, landslides and tsunamis.
The tremors are caused by the disturbance deep down inside the uppermost layer of the earth called the crust. The outermost layer of the earth is not in one piece. It is fragmented. Each fragment is called a plate.
When the plates are in continual motion. When they brush past one another, or a plate goes under another due to Collision, they cause disturbance in the earth's crust. It is this disturbance that shows up as an earthquake on the surface of the earth.
Since earthquakes are caused by the movement of plates, the boundaries of the plates are the weak zones where earthquakes are more likely to occur. The weak zones are also known as seismic or fault zones.
The power of an earthquake is expressed in terms of a magnitude on a scale called the Richter scale.
In the event that an earthquake does strike, take the following steps to protect ourself.
If you are at home
If you are outdoors