Answer
a) $2.089\times 10^{15}W/m^2$
b) $E=1.005\times 10^{-12}J$
Work Step by Step
(a) We know that
$\frac{P}{A}=\frac{E}{\pi r^2 t}$
We plug in the known values to obtain:
$\frac{P}{A}=\frac{2.75\times 10^{-3}J}{(\pi)(17\times 10^{-6}m)^2(1.45\times 10^{-9}s)}=2.089\times 10^{15}W/m^2$
(b) We can find the required energy as follows:
$E=\frac{2.75\times 10^{-3}J}{\pi(17\times 10^{-6}m)^2}(\pi)(\frac{0.650\times 10^{-9} m}{2})^2$
This simplifies to:
$E=1.005\times 10^{-12}J$
