Answer
(a) $0.15mJ$
(b) $3.8KW/cm^2$
(c) $3.8\times 10^5$
Work Step by Step
(a) We know that
$E=P\Delta t$
We plug in the known values to obtain:
$E=(0.75)(0.2)=0.15mJ$
(b) We know that
$I=\frac{P}{A}$
We plug in the known values to obtain:
$I=\frac{0.75\times 10^{-3}}{\pi(2.5\times 10^{-4})}=3.8KW/cm^2$
(c) We can find the required factor as
$\frac{3800W/cm^2}{1.0\times 10^{-2}W/cm^2}=3.8\times 10^5$
