The dielectric in a capacitor serves two purposes. It increases the capacitance,
ID: 1423745 • Letter: T
Question
The dielectric in a capacitor serves two purposes. It increases the capacitance, compared to an otherwise identical capacitor with an air gap, and it increases the maximum potential difference the capacitor can support. If the electric field in a material is sufficiently strong, the material will suddenly become able to conduct, creating a spark. The critical field strength, at which breakdown occurs, is 3.0 MV/m for air, but 60 MV/m for Teflon. What is the maximum energy that can be stored if the plates are separated by a 0.60-mm-thick Teflon sheet? Express your answer using three significant figures.
Explanation / Answer
energy density in between the plates when teflon sheet presents,
u_max = 0.5*epsilon*E_max^2
= 0.5*8.854*10^-12*(60*10^6)^2
= 1.594*10^4 J/m^2
If A is the area of each plate and d is the distance between the plates.
volume of the capacitor, V = A*d
so, maximum energy stored in betwen the plates,
U_max = u_max*V
= 1.594*10^4*A*0.6*10^-3
But A value is not given in the question.
Substitute A in above equation and get U_max.