Will the voltage or potential difference change?

[MIA6]

1. A positive charged rod is held near, but does not touch a neutral electroscope. The charge on the knob becomes
1) positive and the leaves become positive 2) positive and the leaves become negative.
3) - and the leaves become + 4) - and the leaves become -.
I chose 1), but it's wrong. I am not really familiar with electroscope and how they work.

2. There are two positive charged spheres, A and B (A is at the left, B is at the right), 3 meters apart. There is a point x left to the A. If sphere A is moved toward sphere B, the electirc field intensity at point x will
1) decrease 2) increase 3) remain the same
I chose 2) since E=V/d, so when d decreases, E increases. But the answer is 1), so I am wondering if the voltage changes as well? so in general, If there is a change in distance between two charges, will the voltage or potential difference change? if not, then what will affect the potential difference?

Thanks.

 

[Hootenanny]

1. A positive charged rod is held near, but does not touch a neutral electroscope. The charge on the knob becomes
1) positive and the leaves become positive 2) positive and the leaves become negative.
3) - and the leaves become + 4) - and the leaves become -.
I chose 1), but it's wrong. I am not really familiar with electroscope and how they work.

What happens to the electrons in the knob when the positive charge is brought close to them?

 

[fizikx]

The point x is to the left of sphere A...so how does d between sphere A and point x change as sphere A moves towards sphere B?

 

[MIA6]

What happens to the electrons in the knob when the positive charge is brought close to them?

Then there is a redistribution of charge within the object? like the electrons will get to the side where the positive charge is brought to. But then will it stay neutral, and how about the leaves?

 

[MIA6]

The point x is to the left of sphere A...so how does d between sphere A and point x change as sphere A moves towards sphere B?

d between sphere A and point x will also change when A moves toward B because then A is going far away from point x.

 

[Hootenanny]

Then there is a redistribution of charge within the object? like the electrons will get to the side where the positive charge is brought to.

Correct

But then will it stay neutral, and how about the leaves?

Overall, the object is still neutral since there is still the same amount of positive and negative charge on the object. However, if some of the electrons move towards the knob as you correctly say, this means that on the knob there will be more [negative] electrons than [positive] lattice ions; hence the knob will have a net negative charge.

Do you follow?

 

[MIA6]

Correct

Overall, the object is still neutral since there is still the same amount of positive and negative charge on the object. However, if some of the electrons move towards the knob as you correctly say, this means that on the knob there will be more [negative] electrons than [positive] lattice ions; hence the knob will have a net negative charge.

Do you follow?

yes, then what about the leaves?

 

[Hootenanny]

yes, then what about the leaves?

These electrons the move towards the knob, where do you suppose they come from?