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A uniformly charged disk has a radius of 2.5 cm and carries a total charge of 4*10^-12C.

Find the electric field on the x-axis at a distance of 20cm away.

I used the equation:

Ex = (sigma/ (2*Eo)) * (1 - ( 1/ sqrt( ( R^2/x^2) + 1))

this is what i did so far

Ex = (sigma/ (2*8.85*10^-12)*(1 - ( 1/ sqrt( ( 0.025m^2/0.002m^2)-1)

I am not sure how to calculate sigma in this case. I am guessing that it is the total charge dived by the area. But, i think i am missing something.

The answer is 0.89 N/C

Thanks!

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# Homework Help: Electric Charge on a uniformly charged disk

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