This print-out should have 17 questions.Multiple-choice questions may continue onthe next column or page – find all choicesbefore answering.001 10.0 pointsConsider the electromagnetic wave pattern asshown in the figure below.EBWhat is the direction in which the wave istraveling?1. from-left-to-right. correct2. undetermined, since the figure shows astanding wave.3. from-right-to-left.Explanation:
This print-out should have 17 questions.
Multiple-choice questions may continue on
the next column or page – find all choices
001 10.0 points
Consider the electromagnetic wave pattern as
shown in the figure below.
What is the direction in which the wave is
1. from-left-to-right. correct
2. undetermined, since the figure shows a
The direction of traveling is the direction of
E~ × B~ ; i.e., from-left-to-right.
002 10.0 points
A point light source delivers a power P. It
radiates light isotropically (equally in all directions). A mirror of area A is placed at
point B that is at distance r from the source.
The mirror’s surface is perpendicular to the
vector from the source to point B. Make the
approximation that all the light hitting the
mirror is perpendicular to it. The mirror is a
totally reflecting surface.
Find the total force on the mirror.
1. F = P
2. F =
2 π r2 P
3. F = A2 P
2 c π r2
4. F = A P
c 2 π r2 correct
5. F = 4 π r2 P
6. F = P
c 2 π r
7. F = 2 P
8. F = π r2 P c
9. F =
c π r2
10. F =
2 A P
Since the mirror is small enough (or far
enough away) that we may approximate the
incoming light as perpendicular, the force is
F = p A ,
where p is the radiation pressure. The mirror
is totally reflecting, so
Intensity is defined by
I = Power hitting the mirror
Area of mirror A .
P 4πr A 2
4 π r2 ,
leading to a force of
F = p A = 2 I A
c 2 π r2
on the mirror