Answer to #38 is C, Answer to #10 is D, and Answer to #11 is D. 38. Three polari

Question

Answer to #38 is C, Answer to #10 is D, and Answer to #11 is D.

38. Three polarizing sheets are placed in a stack with the polarizing directions of the first and third perpendicular to each other. What angle should the polarizing direction of the middle sheet make with the polarizing direction of the first sheet to obtain maximum transmitted intensity when unpolarized light is incident on the stack? A. 0 B. 30± C. 45± D. 60± E. 90± 10. In a cinema, a picture 2.5 cm wide on the film is projected to an image 3.0 m wide on a screen that is 18 m away. The focal length of the lens is about: A. 7.5cm B. 10cm C. 12.5cm D. 15cm E. 20cm 11. A plane mirror is in a vertical plane and is rotating about a vertical axis at 100rpm. A horizontal beam of light is incident on the mirror. The reflected beam will rotate at: A. 100rpm B. 141rpm C. Orpm D. 200rpm E. 10,00rpm

Explanation / Answer

38. light as passes through the first polarizer,

intensity get halved and it polarized along the axis of polarizer.

then angle is theta then

If = (I0/2) (cos(theta))^2 ( cos(90 - theta))^2

If = (I0 / 2) ( sin(theta) cos(theta))^2

theta = 45 deg

Ans(C)

10. m = - 3 / 0.025 = - 120

m = -q / p = - 120

q = 120 p

q = 18 m then p = 0.15 m

1/f = 1/p + 1/q

f = 0.15 m = 15 cm

Ans(D)

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