Light from a laser forms a 1.31-mm diameter spot on a wall.If the light intensity in the spot is
What is the power output of the laser? Assume that all the light emitted by the laser hits the spot.
A)21.3 mW
B)13.2 mW
C)17.9 mW
D)24.7 mW

Question

Light from a laser forms a 1.31-mm diameter spot on a wall.If the light intensity in the spot is 
What is the power output of the laser? Assume that all the light emitted by the laser hits the spot.
A)21.3 mW 
B)13.2 mW 
C)17.9 mW 
D)24.7 mW

Quizplus · Accepted Answer

The intensity I of light is given by the formula:
I = P/A, where P is the power and A is the area that the light is spread over.
In this case, we have I = 11 × 10^6 W/m^2 and the area of the spot is A = π(0.655 mm)^2 = 1.34 × 10^-6 m^2.
Rearranging the formula to solve for P, we get:
P = I × A = (11 × 10^6 W/m^2) × (1.34 × 10^-6 m^2) = 14.7 mW, which is closest to choice A) 21.3 mW.

Light from a Laser Forms a 1