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Questions and Solutions part 3

1.    When light is incident on a soap film of thickness 5 × 10–5 cm, wavelength reflected maximum in the visible region is 5320 Å. Refractive index of the film will be
    (a) 1.22    (b) 1.33    (c) 1.51        (d) 1.83.

 1187_wave optics solutions.jpg

2.    A ray of unpolarised light is incident on a glass plate of refractive index 1.54 at polarising angle, then angle of refraction is
    (a) 33    (b) 44    (c) 57        (d) 90


 1187_wave optics solutions.jpg

3.    Two waves of same intensity produce interference. If intensity at maximum is 4I, then intensity at the minimum will be     
    (a) 0         (b) 2I    
    (c) 3I        (d) 4I.

Solution - (a) 
    I1 = I2 = I = a2 
    Imax. = (a + a)2 + (2a)2 = 4a2 = 4I 
    Imin. = (a - a)2 = 0

4.    First diffraction minima due to a single slit of width 1.0 x 10–5 cm is at 300. Then wavelength of light used is       
a. 400 Å   b.   500Å    c.   600Å    d.    700Å

 2176_solution 2010.jpg

5.    Light of wavelength   is normally incident on a slit. Angular position of second minimum from central maximum us 300. Width of the slit should be   
    (a) 12 x 10–5 cm        (b) 18 x 10–5 cm    
    (c) 24 x 10–5 cm        (d) 36 x 10–5 cm

 1154_sample wave optics.jpg

6.    A slit 5 cm wide when irradiated by waves of wavelength 10 mm results in the angular spread of the central maxima on either side of incident light by about    
    (a) 1/2 radian         (b) 1/4 radian    
    (c) 3 radian        (d) 1/5 radian.
Solution - (d) 
    Angular spread on either side is given by  
         θ = λ/a = λ/5 radians

7.    In Young's double slit experiment, ten slits separated by a distance of 1 mm are illuminated by a monochromatic light source of wavelength 5 x 10–7 m. If the distance between slit and screen is 2 metre, then separation of bright lines in the interference pattern will be       
    (a) 0.5 mm        (b) 1.0 mm
    (c) 1.5 mm        (d) 1.75 mm

 1603_velocity wave.jpg