physics question please need help?

Question

The Sun delivers an average power of 0.9 W/m2 to the top of Pluto's atmosphere. Find the magnitudes of E max and B max for the electromagnetic waves at the top of the atmosphere.
B max = T
E max = V/m

Answer 1

Hmm... since the waves the sun exhibits are light waves, we'll assume they move at the speed of light. Thus, we have the equation:
E/B = c, where E is the electric field, B is the magnetic field, and c is the speed of light.
From this equation they derived the equation:
I = (Average_power)/A = (E_max)*(B_max)/(2*μ) where I is your intensity, A is your area, and μ is the permeability of free space (μ = 4π * 10^(-7) [T*m/A])

Unfortunately, to use this equation you would have to know the area of the top of the atmosphere of Pluto which is exposed to the Sun's radiation. I'm unsure exactly how to do this without looking it up, but keep in mind that since the Sun is so big, Pluto is so small, and Pluto is so far away, that the rays of light coming from the sun will be essentially parallel. Thus, we can consider the wavefront to be planar, and so the area exposed to the sun's rays will be that of a circle, with a radius measured from the center of Pluto to the top of its atmosphere. If you can find this out, great, otherwise you'll have to use a different approach.