Question 1

Young's double slit experiment is performed in a medium of refractive index of 1.33 . The maximum intensity is I_0. The intensity at a point on the screen, where path difference between the light comi

Accepted Answer

Given, path difference, x= 4 Phase difference, = ( 2 ) (Path difference) = 2 4 = 2 ...(i) It is given that, maximum intensity is I_0. So, intensity at a point on the screen, where phase difference is given by aligned I & =I_0 ^2 ( 2 ) \ & =I_0 ^2 ( / 2 2 ) [ using Eq.(i) ] \ & =I_0 ( 1 2 )^2 \ & = I_0 2 aligned

Question 2

In YDSE, monochromatic light falls on a screen 1.80 m from two slits separated by 2.08 mm . The first and second order bright fringes are separated by 0.553 mm . The wavelength of light used is

Accepted Answer

Position of first bright fringe, y_1= D d Position of second bright fringe, aligned y_2 & = 2 D d \ y_2-y_1 & = 2 D d - D d \ y_2-y_1 & = D d \ or & = (y_2-y_1 ) d D aligned Substituting given values, we have aligned & = 0.553 10^ -3 2.08 10^ -3 1.8 \ & =639 10^ -9 ~m \ or & =639 ~nm aligned

Question 3

A microwave of wavelength 2.0 cm falls normally on a slit of width 4.0 cm . The angular spread of the central maxima of the diffraction pattern obtained on a screen 1.5 m away from the slit, will be:

Accepted Answer

Condition for minima is d = n For Ist minimad = = a = 2 4 = 1 2 =30^ Angular spread =2 =60^

Question 4

The property of light which cannot be explained by Huygen's construction of wavefront is

Accepted Answer

The property of light which cannot be explained by Huygen's construction of wave front is origin of spectra.

Question 5

When a light ray incidents on the surface of a medium, the reflected ray is completely polarized. Then the angle between reflected and refracted rays is

Accepted Answer

According to Brewester's law if the reflected ray is completely polarized, then the reflected and refracted ray is perpendicular to each other. Thus, =90^

Question 6

A single slit of a width a is illuminated by a monochromatic light of wavelength 600 ~nm . The value of ' a ' for which first minimum appears at =30^ on the screen will be :

Accepted Answer

Wavelength of monochromatic light, =600 10^ -9 ~m As fir first minima a = aligned & a 30^ =600 10^ -9 \ & a =1200 10^ -9 ~m =1.2 m aligned

Question 7

The ratio of intensities at two points P and Q on the screen in a Young's double slit experiment where phase difference between two wave of same amplitude are 3 and 2 , respectively are

Accepted Answer

Intensity at a point in Young's double slit experiment is given by I = I _1+ I _2+2 I _1 I _2 Here I _1= I _2= I _0 (say) At P I _ p = I _0+ I _0+2 I _0 3 =2 I _0+2 I _0 1 2 =3 I _0 At Q I _ Q = I _0+ I _0+2 I _0 90^ =2 I _0 I _ P I _ Q = 3 2

Question 8

In a Young's double slit experiment, the intensities at two points, for the path difference 4 and 3 ( being the wavelength of light used) are I_1 and I_2 respectively. If I_0 denotes the intensity pro

Accepted Answer

Resultant intensity in Young's double slit experiment I =4 I _0 ^2 ( 2 ) For path difference 4 phase difference, = 2 4 = 4 I _1=4 I _0 ^2 ( 4 )=2 I _0 For path difference 3 I_2=4 I_0 ^2 ( 2 3 )=I_0 I _1+ I _2 I _0 =3

Question 9

In a young's double slit arrangement frings are produced using light of wavelength 4000 Å. One slit is covered by a thin plate of glass of refractive index 1.4 and the other with another glass plate o

Accepted Answer

As, shift x= ( -1) t Shift due to one plate x_1= ( _1-1 ) t Shift due to another path x_2= ( _2-1 ) t Net shift x= x_2- x_1= ( _2- _1 ) t Also, it is given that x=6 aligned & Hence, 6 = ( _1- _2 ) t \ & t= 6 ( _1- _2 ) = 6 4000 (1.7-1.4) -80000 Å \ & t=8 10^ -6 =8 m aligned

Question 10

Consider the optical system shown in Fig. The point source of light S is having wavelength equal to . The light is reaching screen only after reflection. For point P to besecond maxima, the value of w

Accepted Answer

At P , x= (8 d) 3 d D For 2 nd maxima, x=2 array l 24 d^ 2 D =2 \ = 12 d^ 2 D array

Wave Optics — Previous Year Questions & Solutions