# Homework Help: Coulumb's law problem

1. Oct 16, 2016

### niranjan_learner

1. The problem statement, all variables and given/known data
Two equal and opposite charges are placed at a distance r from each other. A large metallic sheet is placed at a distance d from them as shown in the figure. Due to the presence of the sheet, the attractive force between the charges along the direction joining them:
[Please Note: Figure attached]

1. decreases
2. increases
3. remains unchanged
4. decreases if r > d/2 and increases if r < d/2

2. Relevant equations
Coulombs equation for force between two charges.

3. The attempt at a solution

I attempted the problem by placing image charges -q and +q at a distance d to the left of the metallic plate. In that case the force between the real charges along the line joining them decreases. Is this solution acceptable?

Please review my answer. Thank you!

#### Attached Files:

• ###### prob1.jpg
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2. Oct 16, 2016

### kuruman

Can you provide your reasoning why you think so?

3. Oct 16, 2016

### niranjan_learner

Thank you Kuruman for replying.

My reasoning is as follows:

Lets place the image charges on the left side of the metallic plate. Now the two image charges and the two real charges occupy corners of a rectangle with length 2d and width r with like charges on the diagonally opposite corners. There exists repulsive forces between these like charges. The direction these repulsive forces is along the lines joining them; i. e along the diagonals. The components of these forces along the line joining real charges acts opposite to the attractive force between them. So the force between the real charges along the line joining them decreases.

Please provide your comment on this.

4. Oct 16, 2016

### kuruman

No comment needed. Your reasoning is correct.

5. Oct 16, 2016

### niranjan_learner

Thank you Kuruman. :)

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