Question
(1)A parallel-plate capacitor carrying charge q0 is modified by the insertion of a dielectric with κ = 4.3 between the plates. As a consequence, the energy stored in the capacitor quadruples. What will the charge be after the dielectric is inserted?
(2)A metal sphere of diameter 29 cm carries a charge of 5.6 10-7 C. How much energy is contained in a spherical region of radius 50 cm that is concentric with the sphere?
(2)A metal sphere of diameter 29 cm carries a charge of 5.6 10-7 C. How much energy is contained in a spherical region of radius 50 cm that is concentric with the sphere?
Answers
bobpursley
1) why would charge change? Isn't the capacitor isolated, with no where for the charge to go?
2) Energy= volume*energy density
where energy density is 1/2 epsilon*E^2
so an integration is required
E=kQ/r^2 dVolume= 4PIr^2 dr
energy= int 4PIr^2 (kQ/r^2)^2 dr
2) Energy= volume*energy density
where energy density is 1/2 epsilon*E^2
so an integration is required
E=kQ/r^2 dVolume= 4PIr^2 dr
energy= int 4PIr^2 (kQ/r^2)^2 dr