Answer
(a) $1.9\mu J$
(b) $0.50mJ$
Work Step by Step
(a) We know that
$I=\frac{P_{bulb}}{4\pi r^2}$
We plug in the known values to obtain:
$I=\frac{0.05(150)}{4\pi (2.5)^2}=95.49mW$
Now $E=Pt+LAt=I\pi r^2 t$
$\implies E=(95.49)\pi(0.0025)^2(1.0)=1.9\mu J$
(b) The required energy can be determined as
$E=P\Delta t$
We plug in the known values to obtain:
$E=(0.50)(1.0)=0.50mJ$
