Answer
(a) The intensity of the laser beam is $1.13\times 10^3~W/m^2$
(b) The intensity of the light incident on the retina is $6.37\times 10^6~W/m^2$
(c) The total energy incident on the retina is $1.6\times 10^{-4}~J$
Work Step by Step
(a) We can find the intensity of the laser beam:
$I = \frac{P}{A}$
$I = \frac{P}{\pi~r^2}$
$I = \frac{2.0\times 10^{-3}~W}{(\pi)(0.75\times 10^{-3}~m)^2}$
$I = 1.13\times 10^3~W/m^2$
The intensity of the laser beam is $1.13\times 10^3~W/m^2$
(b) We can find the intensity of the light incident on the retina:
$I = \frac{P}{A}$
$I = \frac{P}{\pi~r^2}$
$I = \frac{2.0\times 10^{-3}~W}{(\pi)(10.0\times 10^{-6}~m)^2}$
$I = 6.37\times 10^6~W/m^2$
The intensity of the light incident on the retina is $6.37\times 10^6~W/m^2$
(c) We can find the total energy incident on the retina:
$E = P~t$
$E = (2.0\times 10^{-3}~W)(80\times 10^{-3}~s)$
$E = 1.6\times 10^{-4}~J$
The total energy incident on the retina is $1.6\times 10^{-4}~J$
