- #1
Spoony
- 77
- 0
Homework Statement
An air-filled capacitor consists of a conducting sphere of radius a, surrounded by a concentric conducting spherical surface of radius b. A charge of 2Q is placed on the inner sphere and –Q on the outer surface. Calculate the electric field strengths E(r), (i) between the two spherical surfaces, i.e. for a < r < b and (ii) for r>b Calculate energy stored in region between 2 surfaces and in region , r> b.
[in this question you may assume that the dialectric constant of air is equal to 1]
Homework Equations
Gauss' law for closed surfaces.
The Attempt at a Solution
I use the standard method of finding the electric field from each using gauss' law and then sum them, but i find my awnser is:
[tex] E(r) = \frac{3Q}{4 \pi \epsilon_{0} r^{2}} [/tex]
When the awnser given is the same but only 2Q rather than 3...
so it seems that only the centre sphere is contributing to the electric field.. but i think i must be wrong.