Light from a Laser Forms a 1 $1.58 \times 10 ^ { 4 } \mathrm {~W} / \mathrm { m } ^ { 2 }$

Multiple Choice

Light from a laser forms a 1.31-mm diameter spot on a wall. If the light intensity in the spot is $1.58 \times 10 ^ { 4 } \mathrm {~W} / \mathrm { m } ^ { 2 }$ what is the power output of the laser? Assume that all the light emitted by the Iaser hits the spot.

A) 21.3 mW
B) 17.9 mW
C) 13.2 mW
D) 24.7 mW