HW 38 - terry (ect328) homework 38 Turner (59130) 1 This...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: terry (ect328) homework 38 Turner (59130) 1 This print-out should have 10 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points A 1 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: 6 . 67128 10 9 N. Explanation: Let : P = 1 mW = 0 . 001 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 . 001 W) 2 . 99792 10 8 m / s = 6 . 67128 10 9 N . 002 10.0 points At what distance from a 68 W electromag- netic wave point source (like a light bulb) is the amplitude of the electric field 22 V / m? o c = 376 . 991 . Correct answer: 2 . 9034 m. Explanation: Let : P = 68 W , E max = 22 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 ) = (22 V / m) 2 2 (376 . 991 ) = 0 . 641925 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 = 68 W . Solving for the radius we get, R = radicalbigg P 4 I = radicalBigg 68 W 4 (0 . 641925 W / m 2 ) = 2 . 9034 m . 003 10.0 points A light wave passes from air into water. Which of the following is true? 1. Its frequency remains unchanged, but its wavelength increases....
View Full Document

Page1 / 5

HW 38 - terry (ect328) homework 38 Turner (59130) 1 This...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online