# Electrostatic Field concept question

1. Jun 1, 2009

### physics213

1. The problem statement, all variables and given/known data

A ping pong ball covered with a conducting graphite coating has a mass .005 kg and a charge -4 microC. What electric field will exactly balance the weight of the ball?

2. Relevant equations

qE = mg

3. The attempt at a solution

I know how to get the magnitude of the electric field using the equation above. I just don't understand the conceptual part of this question: Which way is the electric field going (up or down)? Any help would be appreciated...thanks

2. Jun 1, 2009

### rock.freak667

since weight acts downwards, I'd assume the electric field move the charge upwards.

3. Jun 1, 2009

### harvellt

It would have to act parallel and in the opposite direction to the force of gravity.

4. Jun 1, 2009

### physics213

well another similar problem had the electric field pointing downward with the particle having a negative charge.

5. Jun 1, 2009

### rock.freak667

So which way will the electric field point to move the -4uC charge upwards?

6. Jun 1, 2009

### physics213

I would assume upwards but I'm not really sure. This seems like a really simple concept but i can't figure it out.

7. Jun 1, 2009

### rock.freak667

Electric fields move from positive to negative. So if you place a negative charge in that field, it will move towards the positive side.