HW-22Solutions-03-26-08

# HW-22Solutions-03-26-08 - Lehigh University HW-22 Solutions...

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Lehigh University Physics 21, Spring 2008 March 26, 2008 HW-22 Solutions 22-1. (HRW 33-24) A small laser emits light at power 5.00 mW and wavelength 633 nm. The laser beam is focused (narrowed) until its diameter matches the 1266 nm diameter of a sphere placed in its path. The sphere is perfectly absorbing and has density . What are (a) the beam intensity at the sphere's location, (b) the radiation pressure on the sphere, (c) the magnitude of the corresponding force, and (d) the magnitude of the acceleration that force alone would give the sphere? Solution: 24. (a) We note that the cross section area of the beam is π d 2 /4, where d is the diameter of the spot ( d = 2.00 λ ). The beam intensity is I P d == × × π π 2 3 9 2 92 4 500 10 2 00 633 10 4 397 10 / . ./ .. W m W/m b gc h (b) The radiation pressure is p I c r × × = 2 998 10 132 8 . . . m/s Pa. (c) In computing the corresponding force, we can use the power and intensity to eliminate the area (mentioned in part (a)). We obtain F d p P I p rr r = F H G I K J = F H G I K J = × × π 2 3 2 11 4 167 10 . WP a 3.97 10 W / m N. 9 c hb g (d) The acceleration of the sphere is a F m F d = × ×× ρ (/ ) (. )[( . )( ππ ( 5 . 0 0 1 0 3 3 11 9 3 6 6 167 10 2 00 633 10 314 10 N) kg / m m)] 33 2 22-2. (HRW 33-33) In Fig. 33-42 , a beam of light, with intensity 43 W/m 2 and polarization parallel to a y axis, is sent into a system of two polarizing sheets with polarizing directions at angles of and to the y axis. What is the intensity of the light

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## This note was uploaded on 04/06/2008 for the course PHYSIC 2 taught by Professor Kim during the Spring '08 term at Lehigh University .

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HW-22Solutions-03-26-08 - Lehigh University HW-22 Solutions...

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