1. The problem statement, all variables and given/known data I am doing a problem in my physics textbook where there is two concentric hollow spheres and the space between them is filled with a dielectric substance. The question asks for the electric energy in this space. 2. Relevant equations The only given equation for the C of parallel plate capacitors in my text book is C = A(epsilon)(dielectric constant)/d There is nothing for spherical capacitors Since the problem has two concentric circles, the plate areas are different. I am not sure if this is still the correct formula to use in this case. 3. The attempt at a solution Since the change in voltage is given in the text, I need to calculate the capacitance of the 'capacitor' to find the contained electrical energy. The areas are different, so the equation above for C might not apply. How should I proceed from here? Thank you for helping out! =) EDIT: I'm sorry, I've figured this out already! I used the energy density of the space, which is the energy(electric energy here) over the volume of the space. Energy density is also equal to 1/2 (dielectric const.)(epsilon)(electric field)^2 so I worked my way to the electrical energy. Thanks anyway!