Question

For a science project, you would like to horizontally suspend an 8.5 by 11 inch sheet of black paper in a vertical beam of light whose dimensions exactly match the paper.
If the mass of the sheet is 0.80g , what light intensity will you need?
Express your answer to two significant figures and include the appropriate units.
I = ________.

Answer 1

Answer:

I = 3.9 x 10⁷ W/m²

Explanation:

given,

Sheet of black paper dimension = 8.5 x 11 inch

Area of sheet = 8.5 x 11 = 93.5 inch^2

1 inch =0.0254 m

Area = 0.06032 m²

mass of sheet = 0.80 g

Force = m g =  0.8 x 9.8 x 10⁻³ N

                    =  7.84 x 10⁻³ N

speed of light = c = 3 x 10⁸ m/s

Using equation

$F = \dfrac{IA}{c}$

where I is the intensity of light

$7.84 \times 10^{-3} = \dfrac{I\times 0.06032}{3 \times 10^8}$

$2.352 \times 10^{6} = I\times 0.06032$

$I = \dfrac{2.352 \times 10^{6}}{0.06032}$

I = 3.9 x 10⁷ W/m²

Intensity of the light is equal to I = 3.9 x 10⁷ W/m²