Question

(a) (4 marks) Unpolarised light is incident on a set of three polarising sheets as shown in the figure. The polarising directions of the first and third sheets make angles 01 = 0.0°, and 03 = 90.0° to the vertical, respectively. Find the fraction of the incident intensity that passes through the set of three sheets when 02 is (i) 0°, (ii) 90°, and (iii) 45.00 Air Glass (b) (6 marks) Two rays of light are propagating through a glass block before crossing into the air (see diagram at right). The refractive index of the glass for red light (f = 4.60x10'4 Hz) is 1.54, while the refractive index for purple light (f= 7.00x104 Hz) is 1.55. (The speed of light in air is 2.98x10 m s.) (i) What is the speed of the red light in the glass? (ii) What is the wavelength of the purple light in the glass? (iii) What is the critical angle of incidence (where internal reflection just occurs) for red light inside the glass? (c) (2 marks) Explain why people who go fishing from boats often find polarising spectacles help their underwater vision. (d) (8 marks) An aperture in the form of a narrow slit 0.28 mm wide forms a diffraction pattern on a screen placed 7.0 m away when illuminated with light of wavelength 600 nm. (i) Calculate the width of the central peak of the diffraction pattern (i.e. from minimum to minimum) on the screen. (ii) If instead of using one slit the light illuminates two such slits separated by 0.90 mm, what is the separation of the interference maxima formed on the screen? (iii) Would you expect any of these interference maxima to be missing? Explain your answer.

Answer 1

(b) refractive index nz - ht in a medium - vz c = speed of loght in raeocom - refractwe index 6 speed of red light in glass - v= 2.98 X 10° 1.54 = |o93 x10 m/s. (11) speed of purple in glas V z 2.98 x08 1.55 = 1.9 D x109 ms.

a as speed of a wave wavelength 22 for F purple light, Az 1.92 x W 8 7:00x104 0.2743X10 274.3 nm m If is a then critical Snc a angle I for red, sinc = 1 = 0.6494 1:54 - ... = sin 0.6494 = 10.49
Pls follow one post one question policy  

As 1st question is missing the figure, I am giving you the solution of 2nd.

For third question (c) ans-

Surface of river or sea water reflects part of sun light incident on it. Interestingly reflected light will be plane polarized (partially or fully depending on the angle of the vision). So sun glare from the surface can be minimized by holding a Polaroid in front of the eye. Polaroid cuts off the polarized light from reflected from the upper surface of water and allows the eye to see under water. As light scattered from the water is unpolarized, one can easily see objects-fishes below the water surface.