This preview shows pages 1–2. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: benavides (jjb2356) homework 38 Turner (59130) 1 This printout should have 10 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points A 65 mW laser beam is reflected back upon itself by a mirror. Calculate the force on the mirror. The speed of light is 2 . 99792 10 8 m / s. Correct answer: 4 . 33633 10 7 N. Explanation: Let : P = 65 mW = 0 . 065 W and c = 2 . 99792 10 8 m / s . The intensity of the laser is P A with P the power and A the area of the beam. The average momentum per unit area per unit time (force per unit area) transferred to the wall is p tA = F A = 2 I c = 2 P Ac , so F = 2 P c = 2 (0 . 065 W) 2 . 99792 10 8 m / s = 4 . 33633 10 7 N . 002 10.0 points At what distance from a 8 W electromagnetic wave point source (like a light bulb) is the amplitude of the electric field 17 V / m? o c = 376 . 991 . Correct answer: 1 . 28876 m. Explanation: Let : P = 8 W , E max = 17 V / m , and c = 376 . 991 . The wave intensity (power per unit area) is given by I = S av = E 2 max 2 ( o c ) = (17 V / m) 2 2 (376 . 991 ) = 0 . 383298 W / m 2 . The constant o c (impedance of free space) turns out to be 120 . You should verify that (V / m) 2 = W / m 2 . With this we can find the intensity, which multiplied by the area of a circle of radius R must gives us the sources power P , therefore 4 R 2 I = P = 8 W . Solving for the radius we get, R = radicalbigg P 4 I = radicalBigg 8 W 4 (0 . 383298 W / m 2 ) = 1 . 28876 m . 003 10.0 points A light wave passes from air into water. Which of the following is true? 1. Its wavelength remains unchanged, but its frequency decreases....
View
Full
Document
This note was uploaded on 03/26/2012 for the course PHY 303L taught by Professor Turner during the Spring '08 term at University of Texas at Austin.
 Spring '08
 Turner
 Work

Click to edit the document details