We can reasonably model a 75 W incandescent light bulb as a sphere 6.0 cm in diameter. Typically, only about 5% of the energy goes to visible light; the rest goes largely to non-visible light infrared radiation.

Question

We can reasonably model a 75 W incandescent light bulb as a sphere 6.0 cm in diameter.  Typically, only about 5% of the energy goes to visible light; the rest goes largely to non-visible light infrared radiation.
(a)	What is the visible light intensity (in W/m^2) at the surface of the bulb.
(b)	What are the amplitudes of the electric and magnetic fields at this surface, for a sinusoidal wave with this intensity? 
 
I am really lost on how to solve this problem.  The only thing I know for sure that I need to do is: (75)(.05)=3.75 W for the visible light.  Can you please show your work?

Damon · Answer

find the surface area of the sphere (4 pi r^2) where r = .03 meters then you have .05*75/ surface area Your text has the relationship between intensity and E and B amplitudes.