Question

9. A certain electromagnetic wave has a maximum electric field of 1,000 newtons per coulomb. If the intensity of this wave is 1.34 x 10³ watts, calculate the maximum magnetic field. If this light in incident directly on a perfect reflector with an area of one square meter for a period of 10.0 seconds, what is the momentum provided to the surface?

Answer 1

a) I = [E_max * B_max]/2 $\mu$ _o

so; B_max = 2I $\mu$ _o /E_max = [2 * 4 $\pi$ *10^-7 * 1.34*10³]/1000 = 3.36 $\mu$ T

b) for a perfect reflector; momentum, p =2U/c

where U is the total energy =u/ $\Delta T$

where u = B²/2 $\mu$ _o = (3.36*10^-6)²/(2*4*3.14*10^-7) = 4.49*10-6J

and U = 4.49*10^-6/10 = 4.49*10^-7J/s

and p = 4.49*10^-7 / 3*10⁸ = 1.49*10^-15 J/m