A light with intensity 1000 W/m^2 falls on a surface area of 1 cm^2 and is compl
ID: 1430139 • Letter: A
Question
A light with intensity 1000 W/m^2 falls on a surface area of 1 cm^2 and is completely absorbed. What is the force?I'm using the equation F=IA/c where I is the intensity, A is the area and c is the speed of light but the answer I get is off by about 10^-4. Please help. A light with intensity 1000 W/m^2 falls on a surface area of 1 cm^2 and is completely absorbed. What is the force?
I'm using the equation F=IA/c where I is the intensity, A is the area and c is the speed of light but the answer I get is off by about 10^-4. Please help.
I'm using the equation F=IA/c where I is the intensity, A is the area and c is the speed of light but the answer I get is off by about 10^-4. Please help.
Explanation / Answer
The momentum transferred
p/t = 2(1/c)<I>A.
<I>A = (1000 W/m2)(1*10-4m2) = 0.1 W.
p/t = 2*0.1 W/(3*108 m/s) = 6.67*10-10 kgm/s2.
Each second the wave transfers 6.67*10-10 kgm/s of momentum, F = p/t = 6.67*10-10 N.
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