Important questions based on NCERT syllabus for Chapter 15 - Some Natural Phenomena:
Question-1: Explain charging by friction and charging by induction?
Solution: 1. By rubbing two objects of certain materials, we cause electrons to flow from one object to another, thus creating deficit of electrons in one object, and excess of electrons in another. This causes the bodies to develop charges, and this process is called "Charging by friction."
2. When a charged body, let's say a negatively charged body, is brought close to a neutral body, the positive charges in the uncharged body moves towards the charged body, and the negative charges in the uncharged body will move away from the charged body. This causes a separation of charges in the uncharged body, while the net charge of the body will still be zero. This method is called charging by induction.
Question-2: Explain how Lightning occur in terms of the charges produced by rubbing.
Solution: 1. During the development of a thunderstorm, the air currents move upward while the water droplets move downward.
2. These vigorous movements cause separation of charges. The positive charges collect near the upper edges of the clouds and the negative charges accumulate near the lower edges.
3. There is accumulation of positive charges near the ground also.
4. 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.
5. Negative and positive charges meet, producing streaks of bright light and sound. We see streaks as lightning.
Question-3: The weather department has predicted that a thunderstorm is likely to occur on a certain day. Suppose you have to go out on that day. Would you carry an umbrella? Explain.
Solution: 1. No. We should not carry an umbrella in a thunderstorm.
2. During thunderstorms, which are accompanied with lightning, electric discharge from the clouds can travel through the metallic rod of the umbrella.
3. This may give an electric shock to the person who is carrying it. Hence, it is not safe to carry an umbrella during lightning.