# First post, Electrostatics Questions

## Homework Statement

Options for answers: positive, negative, neutral, cannot tell
1) a positive point charge is brought near the outside surface of a neutral conducting sphere and released. The initial position of the point charge is on the on the positive x axis and the sphere is centered on the origin. The point charge moves in the _______ x direction. (If the point charge does not move, select "Cannot tell".)
2) Two neutral metal spheres, #1 and #2, are mounted on insulating supports. They are connected by a wire. A positively charged glass rod is brought near sphere #1. The wire connecting the spheres is removed and the charged rod is then taken away. Now the charge on sphere #2 is _______ .
3) A negatively charged glass rod repels an object suspended by a non-conducting thread. The charge on the object is _______ .
4) A negatively charged glass rod attracts an object suspended by a non-conducting thread. The charge on the object is _______ .
5) A positively charged ball is brought close to a neutral isolated conductor. The conductor is then grounded, while the ball is kept close. If the ball is first taken away and then the ground connection is removed, the conductor has a _______ charge.

## The Attempt at a Solution

1) I think it is (negative) x directions because it would be attracted to the negative particles and move towards them
2) I think (positive) because the negative particles would move towards the glass rod through the wire and leave the positive particles behind
3) (negative) because negatives repel
4) (cannot tell) because it could be attracted to the positive particles of a neutral object or the object could be positively charged
5) (negative) because the positive particles would be repelled and move down into the earth and would stay there because the ground connection is removed.

I'm not sure where I am going wrong here but I would love some help/insight! Thanks so much :)

phinds
Gold Member
I think you might want to give your answer to 1 some more thought and see how that reflects on some of the other answers.

I think you might want to give your answer to 1 some more thought and see how that reflects on some of the other answers.
number one definitely gave me some trouble. I also thought it possible that it might not move at all, does that sound more likely? Thanks again.

phinds
Gold Member
number one definitely gave me some trouble. I also thought it possible that it might not move at all, does that sound more likely? Thanks again.
Well, think about it this way ... you have stated that it would be attracted by the negative particles. OK, fine. How about the positive particles?

Well, think about it this way ... you have stated that it would be attracted by the negative particles. OK, fine. How about the positive particles?
The positive particles would be repelled, but don't they move to the other side of the sphere? So the negative particles would be on the side close to the rod and the positive particles would stay out of the way on the other side, thus the rod and negative particles would attract each other. This is what I thought happened but I'm sensing that I'm missing something here in this logic.

SammyS
Staff Emeritus
Homework Helper
Gold Member
The positive particles would be repelled, but don't they move to the other side of the sphere? So the negative particles would be on the side close to the rod and the positive particles would stay out of the way on the other side, thus the rod and negative particles would attract each other. This is what I thought happened but I'm sensing that I'm missing something here in this logic.
I'm pretty sure that your analysis is correct for #1.

Why do you assume in your Original Post that your answers are wrong? I think most are correct.

In #5, notice that the positive ball is removed before the ground connection is removed.

I'm pretty sure that your analysis is correct for #1.

Why do you assume in your Original Post that your answers are wrong? I think most are correct.

In #5, notice that the positive ball is removed before the ground connection is removed.
It's an online assignment and when I submit these answers it's not accepted

SammyS
Staff Emeritus