# Energy in EM waves in sphere

## Homework Statement

Sphere of a radius R=50 cm is in nonmagnetic medium of
permittivity ε=4. EM wave with amplitude of electric field Em= 200 V/m is spreading through the medium.
How much energy pass through surface of sphere through 1 minute?

I have couple of question here. Since the sphere is in nonmagnetic medium how will that reflects of her magnetic field?
She doesnt have one?

So here's next flow of mind.I thought of two possibilities.
1) Sav*A*T= ε0*c*E*T
Q: Should i replace ε0 with ε?
Calculating this is quite easy, not sure if correct.

2)
Lets integrate over whole sphere of radius R, to find total Energy/time, that is, total power.
P = ∫sphere Savg
this way is much longer as far as mathemathics, but in the end, it should turn out same.

Are both solutions good?

rude man
Homework Helper
Gold Member
What is the sphere made of? Is it just a spherical volume within the e=4 dielectric, or metallic, or air, or ???

Its just spherical volume within e=4.

rude man
Homework Helper
Gold Member
Its just spherical volume within e=4.
Consider integrating the poynting vector over the sphere's internal "great circle" cross-section.