Charge Behaviour

Q. Five balls numbered 1 to 5 are suspended using separate threads. Pairs (1, 2), (2, 4) and (4, 1) show electrostatic attraction, while pair (2, 3) and (4, 5) show repulsion. Therefore ball 1 must be

1. Positively charged
2. Negatively charged
3. Neutral
4. Made of metal

Q.

What are the mobile charge carriers in a conductor?

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Q. A $1\mu A$ beam of protons with a cross-sectional area of $0.5\text{sq.mm}$ is moving with a velocity of $3\times {10}^{4}m{s}^{-1}$. Then charge density of beam is

1. $6.6\times {10}^{-4}{\text{C/m}}^3$
2. $6.6\times {10}^{-5}{\text{C/m}}^3$
3. $6.6\times {10}^{-6}{\text{C/m}}^3$
4. None of these

Q.

Objects A, B and C are three identical, spherical conductors. Originally A and B both have charges of +3 mC, while C has a charge of –6 mC. Object A and C are allowed to touch, then they are moved apart. Then objects B and C are allowed to touch, and they are moved apart.

If Object A and B are now held near each other, they will

1. attract

2. repel

3. have no effect on each other

4. First attract to a certain position then repel