Damn units and surface charge density.

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SUMMARY

The discussion centers on calculating the surface charge density of a large, flat sheet of charge given a repulsive force of 2.1×10−12 N acting on an electron. The user initially applied the formula F = qE, using the charge of an electron (6.1×10−19 C) to derive the electric field (E). Subsequently, they used the equation E = (surface charge density)/(2ε0) with ε0 = 8.85×10−12 F/m, resulting in an incorrect surface charge density of 2.32×10−42 C/m2. Other users pointed out a calculation error, suggesting the need to verify intermediate results.

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frasifrasi
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Ok, the question asks:

An electron close to a large, flat sheet of charge is repelled from the sheet with a 2.1×10^−12 {N} force.

Q. find the surface charge density on the sheet in C/m^2

What i did was use the formula F = qe with 2.1e-12 for the force and 6.1e-19 for the charge of an electron. This gives me E,which I used in the formula E = (surface charge density)/2epsilon_0.

Plugging everything in (epsilon_0 = 8.85e-12), I get 2.32e-42, but It says it is wrong.

Does anyone know why?

Thanks.
 
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Your formulas are correct, so there's a calculation error somewhere.

2.32e-42 C/m^2 is less than 1 electron per square kilometer!
 


I keep getting it wrong!

Can anyone verify the above is correct?

Much appreciated.
 


frasifrasi said:
Can anyone verify the above is correct?

The above is not correct. It's 2.32 x (A different power of 10 then -42)

Can you show some intermediate results? What did you get for the E-field?
 

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