Question

A typical 100 W incandescent light bulb emits about 3 Watts of light. How much force is exerted on a page of 8.5"x11" white printer paper 0.8 m away? Assume the paper reflects 80% f the light that hits it. g

Answer 1

Answer: 0.0169J/s-m of force will be exerted per sec per meter displacement of the paper

Step-by-step explanation:

Power p = 3W

Distance r = 0.8m

Intensity = p/4¶r^2

Intensity = 3/(4x3.142x0.8^2) = 0.373W/m2

The paper is 8.5" by 11"

Converting to metre becomes

0.2032m by 0.2794m

Are of paper = 0.2032x0.2794 = 0.0568m2

80% of the light reflected is,

0.8x0.373 = 0.2984W/m2

Energy per sec In the reflected light is 0.2984x0.0568 = 0.0169J/s

Force = energy per sec per unit displacement of paper

= 0.0169J/s-m