# Electrical field strength problem

1. Feb 25, 2012

### MMCS

I have completed the force column in the table however im not sure what the question is asking me for the field strength calculation. am i to use the 25μC charge or the 8μC charge in the formula 1/4∏ε x Q/r^2, this may be obvious to someone with more experience of these questions,

Thanks

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2. Feb 25, 2012

### Staff: Mentor

Use the 8μC charge, as that's the charge producing the field that the 25μC charge experiences as per the wording of the problem.

3. Feb 25, 2012

### MMCS

Thanks mate.
I have calculated the force for the 1mm distance to be 1.8x10^6
so for field strength i have used (1.8x10^6)/8μC = 2.25x10^11

4. Feb 25, 2012

### Staff: Mentor

Nope. You should have divided by 25μC thus leaving the 8μC charge in the calculation.

5. Feb 26, 2012

### MMCS

For the table a graph is required, what values do you think they want? would it be force against field strength or would distance be used against another?

6. Feb 26, 2012

### Staff: Mentor

At a guess I'd say two graphs would be appropriate: force vs distance and field strength vs distance. With clever axis labeling you might plot both on the same graph...