Help with Gauss' Law Example

[fouadalnoor]

Hello guys, I am studying for my physics exam and got stuck at this past paper question on gauss's law (attached).

I am probably wrong, but would the solution to i) be:

C = Q/V

V = E*D

Since ∫E*dA = Q/εo

Then:

EA = Q/εo, thus E = Q/(Aεo) , where A = 4Πr^2

Now V = QD/(4Πr^2)

D = b-a

thus:

C = (4Πr^2εo)/(b-a)

ii)

As b tends to infinity

C = 0 F?


Hope you guys can help!

 

[Ratchit]

fouadalnoor,

Hello guys, I am studying for my physics exam and got stuck at this past paper question on gauss's law (attached).

I am probably wrong, but would the solution to i) be:

C = Q/V

V = E*D

Since ∫E*dA = Q/εo

Then:

EA = Q/εo, thus E = Q/(Aεo) , where A = 4Πr^2

Now V = QD/(4Πr^2)

D = b-a

thus:

C = (4Πr^2εo)/(b-a)

ii)

As b tends to infinity

C = 0 F?

No.

Hope you guys can help!

Yes, I can. See the attachment.

Ratch

Whoops, there should be a minus sign in front of the integral