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#### Question 1:

A plastic bag rubbed with cotton wool acquired a positive charge. This happened because:
(a) the plastic acquired extra protons from the cotton.
(b) the plastic acquired extra protons on rubbing.
(c) new protons were created on the plastic while rubbing.
(d) the plastic lost electrons to the cotton during rubbing.

(d) the plastic lost electrons to the cotton during rubbing

A plastic bag rubbed with cotton wool acquires a positive charge because the plastic loses electrons to the cotton during the rubbing and becomes less negative.

#### Question 2:

Which of the following correctly shows what happens when a positively charged rod is brought close to an electroscope?
Figure

Figure (a) correctly shows what happens when a positively charged rod is brought close to an electroscope.

The near end of the electroscope acquires the opposite (negative) charge because of induction, whereas the far end acquires the same (positive) charge.

#### Question 3:

A negatively charged balloon is brought near a neutral metal sphere as shown. Which one of these diagrams correctly shows the distribution of charges on the metal sphere?
Figure

Figure (c) correctly shows the distribution of charges on the metal sphere.

Owing to induction, the near end acquires the opposite charge, whereas the far end acquires the same charge as that of the balloon.

#### Question 4:

The sentences below explain why you sometimes get an electric shock on touching a door knob. But they are all jumbled up. Which is the correct sequence of events?
A. Electrons move from the floor to your body.
B. And you get a shock.
C. The metal door knob is a conductor.
D. You walk wearing nylon socks.
E. The extra electrons move from your body to the door knob.
F. Your feet rub against the floor.
G. Now you have extra electrons.

(a) D, F, E, G, C, A, B
(b) D, F, A, G, C, E, B
(c) B, E, C, G, A, F, D
(d) B, A, C, G, E, F, D

(b) D, F, A, G, C, E, B

D. You walk wearing nylon socks.

F. Your feet rub against the floor.

A. Electrons move from the floor to your body.

G. Now you have extra electrons.

C. The metal doorknob is a conductor.

E. The extra electrons move from your body to the doorknob.

B. And you get a shock.

#### Question 5:

Which of the following will attract bits of paper on being rubbed with silk?
(a) metal ruler
(b) steel spoon
(c) pencil
(d) spokes of a cycle wheel

(c) pencil

Rubbing with silk creates a static charge on a pencil made of wood. As wood is an insulator, any electrons that it gains stay where they are instead of flowing away.

#### Question 6:

When electrons are removed from an atom, then it is called ______________.
(a) a molecule
(b) a nucleus
(c) an ion
(d) a gas

(b) a nucleus

When electrons are removed from an atom, it is called a nucleus.

#### Question 7:

Neutral atoms have the same number of
(a) protons and electrons.
(b) protons and neutrons.
(c) electrons and neutrons.
(d) atoms and ions.

(a) protons and electrons

Neutral atoms have the same number of protons and electrons.

#### Question 8:

An electroscope charged by induction using a glass rod rubbed with silk becomes
(a) positively charged.
(b) negatively charged.
(c) neutral.
(d) can't say, incomplete information

(a) positively charged

A glass rod rubbed with silk acquires a static charge, and when the rod is used to charge an electroscope by induction, the electroscope acquires the same charge.

#### Question 9:

What happens if these two electroscopes are connected by a wire?
A. The leaves of 1 would diverge further.
B. The leaves of 1 would come closer.
C. The leaves of 2 would also diverge.
D. Nothing would happen.

(a) both A and B are correct.
(b) only B is correct.
(c) both B and C are correct.
(d) only D is correct.

(b) only B is correct

Electrons will move from 2 to 1, so 1 will become less positive.

#### Question 10:

An atom of sodium containing 11 protons, 12 neutrons and 10 electrons
(a) is neutral.
(b) is positively charged.
(c) has a surplus of one electron.
(d) is negatively charged.

(b) is positively charged

The atom has a surplus of one proton, which has a positive charge.

#### Question 11:

State the Law of Electrostatic Attraction and Repulsion.

The law of electrostatic attraction and repulsion states that 'two like charges repel each other and two unlike charges attract each other'.

#### Question 12:

Indicate, giving reasons, if the following statements are true or false.
(a) An object which is positively charged contains only protons and no electrons.
(b) An atom with 11 electrons, 11 protons and 12 neutrons is electrically neutral.
(c) An object that is electrically neutral will contain only neutrons.
(d) Two straws rubbed with silk will attract each other.
(e) A balloon rubbed with wool will repel another one that is not rubbed.
(f) When a glass rod is rubbed with silk and made to touch an electroscope, its leaves diverge as they acquire similar charges from the rod.
(g) An electroscope charged by induction develops the same kind of charge as that of the charging body.
(h) To charge an electroscope by conduction, it must be touched by a charged body.
(i) Like charges attract each other while unlike charges repel each other.

(a) False
An object that is positively charged has a greater positive charge and a lower negative charge.

(b) True
An atom that has 11 protons and 11 electrons is electrically neutral, because it has the same number of unlike charges, i.e., protons and electrons, and because the neutrons have no charge.

(c) False
An object that is electrically neutral contains neutrons and the same number of unlike charges, i.e., electrons and protons.

(d) False
Two straws rubbed with silk move away from each other because they acquire the same kind of charge.

(e) True
A balloon that is rubbed with wool acquires static electricity, and when it is brought near an uncharged balloon, the near end of the uncharged balloon acquires the same kind of charge  due to induction. So, the balloons repel each other.

(f) True
A glass rod acquires a positive charge when it is rubbed with silk. When it is made to touch an electroscope, electrons move from the electroscope to the glass rod, and the leaves of the electroscope acquire a positive charge similar to the charge on the glass rod, and diverge.

(g) True
The leaves of an electroscope charged by induction acquire the same kind of charge owing to induction.

(h) True
To charge an electroscope by conduction, it must be touched by a charged body, so that the charge moves from one body to the other.

(i) False
Like charges repel and unlike charges attract each other.

#### Question 13:

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? Explain your answer. Now what will happen if you touch the electroscope?

A charged rod is negatively charged, so the near end of the electroscope rod acquires an opposite charge, i.e., positive charge, by the process of induction, whereas the far end becomes more negative. So, the leaves of the electroscope diverge further.

#### Question 14:

Fill in the blanks.
(a) An atom consists of _______________, ____________ and _____________.
(b) _____________ are negatively charged particles, while ____________ are positively charged and ____________are ____________.
(c) The ____________ at the center of the atom has ___________ and ____________.
(d) The paths of the negatively charged particles in an atom are called ______________.
(e) Each _____________ is a unit of negative electricity.
(f) In an atom, the _____________ and ____________ are equal in number.
(g) The ___________ and ____________ together make up most of the mass of an atom.
(h) The _____________ of an ____________ is negligible.
(i) The atom as a whole is electrically ______________.
(j) An atom with a shortage or surplus of _____________ is called an ____________.

(a) An atom consists of electrons, protons and neutrons.

(bElectrons are negatively charged particles, while protons are positively charged and neutrons are neutral.

(c) The nucleus at the center of the atom has protons and neutrons.

(d) The paths of the negatively charged particles in an atom are called orbit.

(e) Each electron is a unit of negative electricity.

(f) In an atom, the electrons and protons are equal in number.

(g) The protons and neutrons together make up most of the mass of an atom.

(h) The mass of an electron is negligible.

(i) The atom as a whole is electrically neutral.

(j) An atom with a shortage or surplus of electrons is called an ion.

#### Question 15:

On a cold, dry day, a child takes two balloons and rubs them against his sweater.
(a) When taken near each other, the balloons repel each other.
(b) When one is taken near the wall, it sticks to it.
Give reasons for the above observations.

(a) The balloons acquire the same kind of charge on rubbing, so they repel each other.

(b) When a charged balloon is brought near an uncharged wall, induction occurs, and the wall acquires a charge opposite to that of the balloon. As the balloon and the wall now have opposite charges, they are attracted to each other.

#### Question 16:

A negatively charged metal sphere is fixed to a wooden stand. What will happen if it is
(a) touched by a neutral glass rod
(b) touched by a metal rod
Figure

(a) The metal sphere remains negatively charged as the glass rod is an insulator.

(b) The metal sphere becomes neutral, because excess electrons move from it to the metal rod.

#### Question 17:

Give reasons for the following:
(a) Your hair stands on its ends while removing a sweater or when you pull off your hat.
(b) You see a streak of lightning before you hear the thunder associated with it.
(c) A rice grain tied to a thread is attracted to a plastic comb that was just used to comb hair.
(d) Anand found that balloons rubbed with his sweater did not stick to the walls of his bathroom where he had just taken a bath with hot water.

(a) Our hair stands on end while we remove a sweater or our hat because it acquires static electricity owing to friction.

(b) We see lightning before we hear thunder because light travels much faster than sound.

(c) On combing hair, a plastic comb acquires static electricity, so when it is brought near a rice grain, the grain gets attracted towards it.

(d) A wet wall acts like a conductor, and when a charged balloon is brought near it, the charges move from the balloon to the wall, and the balloon gets discharged.

#### Question 18:

In 'A', a plastic comb is held near a very thin stream of water. In 'B', the same comb, after being used to comb hair, is kept exactly in the same position.
Figure

(a) What happens to the water in 'B'?
(b) What is different about the comb in 'B'?
(c) What has caused the comb to change?
(d) Why did the stream get deflected in 'B'?
(e) If you use a glass rod instead of a comb, what will be the effect?

(a) It gets attracted towards the comb.

(b) The comb in 'B' is charged.

(c) On being used for combing hair, the comb acquires static electricity.

(d) The stream of water gets deflected in 'B' because it is attracted towards the comb owing to induction.

(e) The effect will be the same, because a glass rod is also an insulator like a plastic comb.

#### Question 19:

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?

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.

#### Question 20:

(a) If an electroscope is charged by conduction using a glass rod rubbed with silk, what charge will be developed on the leaves of the electroscope?
(b) If the same glass rod is used to charge the electroscope by induction, what charge is developed on the leaves?
(c) If the charged electroscope is touched with a wooden rod, what happens?

(a) If an electroscope is charged by conduction using a glass rod rubbed with silk, a positive charge is developed on the leaves of the electroscope. A glass rod acquires a positive charge when it is rubbed with silk, and when it is made to touch an electroscope, electrons move from the electroscope rod to the glass rod, and the leaves of the electroscope acquire a positive charge and diverge.

(b) If the same glass rod is used to charge the electroscope by induction, then a positive charge is developed on the leaves of the electroscope. This is because the glass rod is positively charged, and so the near end of the electroscope rod acquires the opposite charge, i.e., negative charge, by the process of induction. However, the far end becomes positively charged, and the leaves of the electroscope diverge.

(c) If the charged electroscope is touched with a wooden rod, then no changes take place, because wood is an insulator.

#### Question 21:

Explain what kind of charges develop on B and A when C is brought near them. What is the method of charging in A and B known as?
Figure

When C is brought near B, B acquires a positive charge by the process of induction, whereas, when C is brought near A, A acquires a negative charge by the process of conduction.

#### Question 22:

Two charged bodies A and B were each brought near an electroscope as shown. When A is brought near the electroscope, the leaves of the electroscope diverge further. When B is brought near the electroscope, the leaves of the electroscope collapse. Give reasons and identify the charges on A and B.
Figure

When A is brought near the electroscope, the leaves of the electroscope diverge further, because A is positively charged. When A is brought near the electroscope, more negative charge starts accumulating on the disc of the electroscope by the process of induction, whereas the far end becomes more positive, so the leaves of the electroscope diverge further.
When B is brought near the electroscope, the leaves of the electroscope collapse, because B is negatively charged. When B is brought near the electroscope, the negative charge on the disc of the electroscope starts moving towards the leaves of the electroscope by the process of induction, so the leaves of the electroscope becomes less positive and collapse.

#### Question 23:

A metal ball mounted on an insulated stand is given an electric charge. It is then touched with a rod, one end of which is held in the hand. What happens to its charge if the rod is made from one of these materials?
(a) a good insulator
(b) a poor insulator
(c) a good conductor

(a) If the rod is made of a good insulator, the metal ball remains charged.

(b) If the rod is made of a poor insulator, the metal ball loses some charge.

(c) If the rod is made of a good conductor, the metal ball gets discharged.

#### Question 24:

If you slide out of a car seat on a cold, dry day, you can get an electric shock when you touch the car body. If you hold on to the body of the car as you slide out, this does not happen. Why is this so?

If we slide out of a car seat on a cold, dry day, we can get an electric shock when we touch the car body. This happens because the static charges built-up on our body discharges to the metallic body of the car.
If we hold on to the body of the car as we slide out, this does not happen. This can be explained thus: The body of the car is made of a metal, which is a good conductor of electricity, and so the excess charge in our body
, developed from friction with the seat, moves through the body of the car. Therefore, we do not get an electric shock.

#### Question 25:

Rohan rubbed a plastic ruler to his hair and then took the ruler close to bits of paper. The bits of paper got attracted to the ruler. But when Suresh tried the same with a metal ruler, the bits of paper did not stick to the ruler. He was very confused. Can you explain why this happened?

A metal ruler is a conductor, so the charge of whatever kind it acquires on rubbing against hair flows through the ruler to our body. The ruler gets discharged and does not attract the paper bits. However, a plastic ruler, being an insulator, acquires static electricity on rubbing against hair and attracts the paper bits when brought closer to them.

#### Question 26:

Explain how a lightning conductor protects a building?