Electric Field Strength of Cylinder Capacitor at Inner Radius

[universitypq98]

capacitance cylinder

Homework Statement

Hey guys! :)
I have an exam tomorrow i am a stuck with this question while reviewing :S..
Can anyone help me please?

consider a cylinder capacitor of length 1m , inner radius 0.1cm and outter radius 0.2cm. You connect the capacitor to a 10V battery. What is the electric field strength at the inner radius?
a) 0v/m
b)infinity
c)7.7 kv/m
d)14.4kV/m

Homework Equations

C= k*L/ln(b/a)
q=C*V
E=V/d
E=k*q/R^2

The Attempt at a Solution

first capacitance of a cylindrical capacitor is known to be
C=K*L/ln(b/a) (b=0.5/a=0.1)
then i thought to calculte the charge q=C.V
but i can't see the relation to find the electric field E :S
and also the thing about the inner radium made me confused..

 

[ehild]

You see a cylindrical capacitor in the figure. Try to use Gauss' Law to get the electric field at the inner radius r=0.1 cm.

ehild

 

[universitypq98]

will it be =0?? cause in the inner radius no charges?

this is gauss law : E=q/epsilom0*A :S
i tried the calculation no answer fits mine.. so i thought it might be 0 because it is in the inner radius?
Sorry if it seems that i am so narrow minded.. i have been studying physics since this morning,got look of chapters and exams coming this week..
Thanks again! i really appreciated your help

 

[universitypq98]

i think i have found it! :D
narrow minded me.. tonight.. because tired.. mixing the formulas..
the true formula is :
C= 2pii*eps0*L/ln(b/a)
then q=c*v
and then E=q/eps0*A(gauss law)!
and i got the last choice 14.4kV/m!

Just one more thing.. can anyone track me if it is correct?? you gave me this procedure,did i used it in the right way?

Evening! and thanks a lot!

 

[ehild]

It is correct.

ehild

 

[universitypq98]

good morning ehild :)
Thanks a lot!
wish me luck please.. my exam is in 3h (Y) :P
have a nice day!

 

[ehild]

Good luck! By the way, do not forget to use parentheses in your equations. You forgot them in your post.

ehild