# The mirror’s surface is perpendicular to the vector from...

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EM waves and particles yeazell (58010) 1 This print-out should have 17 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0points Consider the electromagnetic wave pattern as shown in the figure below. E B What is the direction in which the wave is traveling? F = π r 2 P c 2. F = P c 3. F = 2 A P c r 2 4. F = P c 2 π r 5. F = 2 P c 6. F = 2 P c π r 2 7. F = 2 π r 2 P c A 2 8. F = A P c 2 π r 2 correct 2 P c A 1. from-right-to-left. 2. from-left-to-right. correct 3. undetermined, since the figure shows a standing wave. Explanation: The direction of traveling is the direction of vector E × vector B ; i.e. , from-left-to-right. 9. F = 4 π r 10. F = A 2 P 2 c π r 2 Explanation: Since the mirror is small enough (or far enough away) that we may approximate the incoming light as perpendicular, the force is simply F = p A , where p is the radiation pressure. The mirror is totally reflecting, so p = 2 I c . 002 10.0points A point light source delivers a power P . It radiates light isotropically (equally in all di- rections). A mirror of area A is placed at point B that is at distance r from the source. Find the total force on the mirror. 1. F = π r 2 P c 2. F = P c 3. F = 2 A P c r 2 4. F = P c 2 π r 5. F = 2 P c 6. F = 2 P c π r 2 7. F = 2 π r 2 P c A 2 8. F = A P c 2 π r 2 correct 2 P c A
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. B r Intensity is defined by I = Power hitting the mirror Area of mirror A . I = P parenleftbigg A 4 πr 2 parenrightbigg A = P 4 π r 2 , leading to a force of F = p A = 2 I A c = A P c 2 π r 2 on the mirror.
EM waves and particles yeazell (58010) 2 keywords: 003 10.0points An unpolarized light beam with intensity of I 0 passes through 2 polarizers shown in the picture. 004 10.0points A helium-neon laser emits light of wavelength 632 . 8 nm and has a power output of 1 mW. How many photons are emitted per second by this laser? = 3 I 0 8
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