A. On earth, the time-averaged flux of electromagnetic energy ((S)) from the sun

Question

A. On earth, the time-averaged flux of electromagnetic energy ((S)) from the sun is 0.14 watt/cm^2. Consider steady sunlight hitting 1 m^2 of earth: picture an imaginary box (containing streaming sunshine) striking this area, with a "box height" of 1 light-second. There is a certain amount of momentum stored in that box, and in one second, ALL that momentum will strike the 1 m^2 area. Assuming the EM wave is absorbed (not reflected), what force does that work out to? How does the radiation pressure from this light compare to atmospheric air pressure, Comment! -If the earth reflected the sunlight, how would that affect the radiation pressure (qualitatively)?

Explanation / Answer

The intensity of light is

I = 0.14 W /cm^2 = 1400 W/m^2

Now the radiation pressure for absorbed light is

p = I / c = 1400 / ( 3 x 10^8) = 4.67 x10^(-6) pascal

Now the force on 1 m^2 area is

F= pA = 4.67 x 10^(-6) Newton.

b)

The intensity of light is

I = 0.14 W /cm^2 = 1400 W/m^2

Now the radiation pressure for reflected light is

p = 2I / c = (2) 1400 / ( 3 x 10^8) = 9.33 x10^(-6) pascal

Now the force on 1 m^2 area is

F= pA = 9.33 x 10^(-6) Newton.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---