Answer
(a) The intensity of the light just outside the laser is $7.96\times 10^5~W/m^2$
(b) The intensity of the light where it hits the surface of the moon is $1.76\times 10^{-9}~W/m^2$
Work Step by Step
(a) We can find the intensity of the light just outside the laser:
$I = \frac{P}{A}$
$I = \frac{P}{\pi~r^2}$
$I = \frac{10~W}{(\pi)(2.0\times 10^{-3}~m)^2}$
$I = 7.96\times 10^5~W/m^2$
The intensity of the light just outside the laser is $7.96\times 10^5~W/m^2$
(b) We can find the intensity of the light where it hits the surface of the moon:
$I = \frac{P}{A}$
$I = \frac{P}{\pi~r^2}$
$I = \frac{10~W}{(\pi)(4.25\times 10^4~m)^2}$
$I = 1.76\times 10^{-9}~W/m^2$
The intensity of the light where it hits the surface of the moon is $1.76\times 10^{-9}~W/m^2$
