Static Electricity Important Questions

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Important Questions on Static Electricity

Ques 1. State the law of conservation of electric charge. (2 marks)

Ans. The law of conservation of electric charge states that the net amount of electric charge produced in any process is zero; i.e., no net electric charge can be created or destroyed.

Ques 2. After some time of rubbing a glass rod with a woollen cloth, the charges again become neutral. Where do the charges go? (2 marks)

Ans. When objects are charged by rubbing, they hold their charge only for a limited time and return to the neutral state. Usually, the excess charge dissipates onto water molecules in the air as water molecules are polar. A positively charged object, on the other hand, can be neutralized by the transfer of loosely held electrons from water molecules in the air.

Ques 3. Why do conductors, insulators, and semiconductors behave differently? (3 marks)

Ans. Conductors are those which easily conduct electricity. Insulators are those which do not conduct electricity and semiconductors are those which lies in between conductors and insulators.

In a conductor, there are many conducting electrons which help in the conduction of electricity. While in a semiconductor there are very few conducting electrons and in an insulator, there would be none.

Ques 4. What are the different ways that can charge an uncharged metal rod? (2 marks)

Ans. There are three primary methods of charging an uncharged metal rod. 

1. Charging by Conduction 
2. Charging by induction 
3. By grounding the metal rod first and then bringing a charged object near the given metal rod and quickly disconnecting the rod from the ground.

Ques 5. What is Charging by Induction? (2 marks)

Ans. Charging by induction is method of charging without any physical contact. If a charged object is brought near a conducting surface, even without physical contact, electrons will move in the conducting surface. 

Ques 6. Explain how charging is done by Conduction. (3 marks)

Ans. Imagine a positively charged metal object A is brought close to an uncharged metal object B. If the two objects touch, the free electrons in the neutral one are attracted to the positively charged object and some of those electrons will transfer to the other object.

Since object B, originally neutral, is now missing some of its negative electrons, it will have a net positive charge. This process is called charging by conduction, or “by contact,” and the two objects end up with the same charge.

Ques 7. What are some of the dangers of static electricity? (5 marks)

Ans. Some of the dangers of static electricity are:

1. Lightning carries charges and if we get struck by lightning, it proves to be fatal as they carry million of volts.
2. Sparks from static electricity can be dangerous when flammable vapour like LPG is present 
3. Dust and germs are attracted by charged objects. Thus it is important to maintain proper sanitation in operation rooms and labs. 
4. Computers are vulnerable to electrostatic damage

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Ques 8. What are the uses of static electricity? (5 marks)

Ans. Some of the real-life applications of static electricity are:

a) Flue-ash precipitation

An electrostatic precipitator is a device used to remove the dust and ash that goes up the chimneys of coal-burning power stations. It consists of a charged fine wire mesh which produces a similar charge to the rising particles of ash. They are then attracted to plates with an opposite charge. These fall to the ground after the charge is gone which is then collected and cleaned.

b) Photocopiers

Photocopiers contain a charged drum and when the paper to be copied is laid on the glass plate, the light reflected from the white parts of the paper causes the charge to disappear from the corresponding parts of the opposite drum. The charge pattern remaining on the drum corresponds to the dark-colored printing on the original. Special toner powder is then dusted over the drum and sticks to the charged parts. When a sheet of paper passes over the drum, the particles of toner are attracted to it and fused into place by a short release of heat.

c) Inkjet printers

In an inkjet printer, tiny drops of ink are forced out of a fine nozzle. These drops are charged electrostatically, and then passed between two oppositely charged plates. A negatively charged drop will be attracted towards the positive plate causing it to be deflected. The amount of deflection and position at which the ink strikes the page is determined by the charge on the drop and the potential difference between the plates. About 100 precisely located drops are needed to make up an individual letter.

Ques 9. When a charged rod is brought near a negatively charged electroscope, the leaves diverge more. What do you think is the charge on the rod? What will happen if you touch the electroscope? Explain your answer. (2 marks)

Ans. A charged rod is negatively charged. By the way of charging by conduction, the near end of the electroscope rod acquires an opposite charge, i.e., positive charge. Due to this, the far end becomes more negative. So, the leaves of the electroscope diverge further.

Ques 10. A charged rod is allowed to touch the disc of a negatively charged electroscope. The divergence of the leaves is considerably reduced. What type of charge did the rod have? (2 marks)

Ans. The charged rod has a positive charge, and when it is allowed to touch the disc of a negatively charged electroscope, it acquires a negative charge by the process of conduction. However, the far end of the electroscope becomes less negative, so the divergence of the leaves of the electroscope decreases.

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