Solve problems (a) and (b) below. Sorta) If a laser beam (with a large enough di

Question

Solve problems (a) and (b) below. Sorta) If a laser beam (with a large enough diameter D) could levitate a human being. how much power should it have? Assume a human being has weight 680 N, and is basically a (non-reflecting) cylinder with a circular cross-sectional area A. and the laser is directed upward at the bottom A, as shown. (b) In the figure, a beam of unpolarized light with intensity I goes through a pair of polarizing sheets with transmission axes oriented at angles , and 02 (both measured counter- clockwise from the +y axis.). If ,-20, find the angle 0, needed to reduce the light's intensity to one fifth of I 02

Explanation / Answer

(A) Fnet = F - W = 0

F = 680 N

and F = Power / C

P / (3 x 10^8) = 680

P= 2.04 x 10^11 Watt

(b) after pass through 1st,

I1 = I / 2

after that.

If = I1 (cos(theta2 - theta1))^2

I/5 = (I/2) (cos(theta2 - 20))^2

cos(theta2 - 20 ) = 0.632

theta2 - 20 = 50.8

theta2 = 70.8 deg

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