# Total Charge on the Surface of a Drum

1. Jan 25, 2012

### y0tsubato

Hi everyone-This is my first time posting a homework question. I'm a little stuck. I appreciate any help to clue me in the right direction.

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

If the drum has a surface area of 6.25×10−2 , what total quantity of charge must reside on the surface of the drum?

I got this right by using Q=EA ϵ0

If the surface area of the drum is increased to 0.124 so that larger sheets of paper can be used, what total quantity of charge is required to produce the same 1.30×105 electric field just above the surface?

2. Relevant equations

permittivity of free space to be = 8.85×10−12
Q=EA ϵ0
electric field = 1.30*10^5
surface area= 6.25*10^-2

3. The attempt at a solution

(8.85*10^-12)(0.124)(6.25*10^-2)
I used the above because I thought it would be just a matter of multiplying the surface area and dividing by the electric field.

2. Jan 26, 2012

### y0tsubato

The solution was very easy once I understood. My main problem was interpreting the phrase, "increased to". I kept trying to use the original surface area given.