# Electric field lines between 20/30 V point charges vs. 10/0 V

1. Jul 13, 2013

### miaou5

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

What would the electric field lines / equipotential lines look like between point charges that are set up with potentials of 20 volts and 30 volts versus point charges that are set up with potentials of 0 volts and 10 volts?

3. The attempt at a solution

At first I thought the electric field lines would look different, but the more I thought about it, the more it seemed like they would be the same, since only the difference in V counts as opposed to the "absolute" values of V. Is this correct? Thank you all so much!

Added question: I completely forgot about this, but would the lines extend from the 10 V charge toward the 0 V? I know the lines go from the positive charge from the negative charge, so I'm pretty sure they would go from the higher V to the lower V, but I just wanted to make sure. Thank you!

2. Jul 13, 2013

### BruceW

It is true that only difference of voltage is important but remember the convention about voltage at infinitely far away. This is important for this problem.

3. Jul 16, 2013

### miaou5

Thank you so much!

4. Jul 16, 2013

### BruceW

hehe. no problem!

5. Jul 17, 2013

### willem2

What is a point charge set up with a potential of 20 V ?

Since the potential due to a point charge is

$$\frac {1}{4 \pi \epsilon_0} \frac {Q}{r}$$

the potential near a point charge will become infinite for any non-zero charge.
If the point charge is merely a very small sphere, you still need to know the radius to get the charge from the potential.