Does Light in a Box Have Momentum?

DrPapper · Jun 2, 2016

Homework Statement

Printed physics problem text asking for the force and radiation pressure of sunlight striking 1 square metre of Earth, using a light-filled imaginary box of 1 light-second height, and whether pressure changes if the light is reflected.

Homework Equations

<S>=c[itex]\epsilon[/itex]E²/2

[itex]\Delta P = A \Delta t <S>/c[/itex]

The Attempt at a Solution

My question is if we need the "box height"? This is my work which I'm assuming is wrong. :C

Handwritten solution: P = 1000 W m^-2 / c ≈ 3.34 × 10^-6 N/m^2, since A = 1 m^2, then F = 3.34 × 10^-6 N. Bullets state the pressure of light is negligible compared to the atmosphere and reflection does not change the value of the pressure.

If there's another problem like this on here please put a link. I didn't see any, but my search terms may not have been ideal "Pressure of light in a box".

DrClaude · Jun 2, 2016

What is the momentum of the light? Why did 1400 W m^-2 become 1000 W m^-2? You didn't say why reflection doesn't change the answer.

Does Light in a Box Have Momentum?

Homework Statement

Homework Equations

The Attempt at a Solution

Discussion

Similar threads