   Chapter 29, Problem 85PE

Chapter
Section
Textbook Problem

Integrated ConceptsThe momentum of light is exactly reversed when reflected straight back from a mirror, assuming negligible recoil of the mirror. Thus the change in momentum is twice the photon momentum. Suppose light of intensity 1.00 kW/m2 reflects from a mirror of area 2.00m2. (a) Calculate the energy reflected in 1.00 s. (b) What is the momentum imparted to the mirror? (c) Using the most general form of Newton's second law, what is the force on the mirror? (d) Does the assumption of no mirror recoil seem reasonable?

(a)

To determine

The energy reflected in 1.00s.

Explanation

Given Data:

The momentum of light is exactly reversed when reflected straight back from a mirror, assuming negligible recoil of the mirror. Thus, the change in momentum is twice the photon momentum. Assume the light of intensity 1.00kW/m2 reflects from a mirror of area 2.00m2 .

Formula Used:

The reflected back energy is calculated as follows:

E=IA

Where I= Intensity

A= Area

Calculation

We have A=2.00m2 and I=1.00kW/m2=1

(b)

To determine

The momentum imparted to the mirror.

(c)

To determine

The force on the mirror.

(d)

To determine

If the assumption of no mirror recoil reasonable.

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