16. If yellow light emitted by sodium lamp in Young’s double slit experiment is replaced by a monochromatic blue light of the same intensity

1. 1. fringe width will decrease

   
   
   

   2. fringe width will increase

   
   
   

   3. fringe width will remain unchanged

   
   
   

   4. fringes will become less intense

   
   
   

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1. View Hint View Answer Discuss in Forum

   As β =	λD	and λb < λy,
   	d

   
   ∴ Fringe width β will decrease

   Correct Option: A

   As β =	λD	and λb < λy,
   	d

   
   ∴ Fringe width β will decrease

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17. Which of the following phenomenon is not common to sound and light waves ?

1. 1. Interference

   
   
   

   2. Diffraction

   
   
   

   3. Coherence

   
   
   

   4. Polarisation

   
   
   

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1. View Hint View Answer Discuss in Forum

   Sound waves can not be polarised as they are longitudinal. Light waves can be polarised as they are transverse.

   Correct Option: D

   Sound waves can not be polarised as they are longitudinal. Light waves can be polarised as they are transverse.

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18. The Young’s double slit experiment is performed with blue and with green light of wavelengths 4360 Å and 5460 Å respectively. If x is the distance of 4th maxima from the central one, then

1. 1. x (blue) = x (green)

   
   
   

   2. x (blue) > x (green)

   
   
   

   3. x (blue) < x (green)

   
   
   

   4. 	x (blue)	=	5460
      	x (green)		4360

   
   
   

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1. View Hint View Answer Discuss in Forum

   Distance  of nth maxima,
   

   x = nλ	D	∝ λ
   	d

   
   As λ_b < λ_g
   &htere4; λ_blue < λ_green

   Correct Option: C

   Distance  of nth maxima,
   

   x = nλ	D	∝ λ
   	d

   
   As λ_b < λ_g
   &htere4; λ_blue < λ_green

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19. In Young’s double slit experiment, the fringe width is found to be 0.4 mm. If the whole apparatus is immersed in water of refractive index 4/3, without disturbing the geometrical arrangement, the new fringe width will be

1. 1. 0.30 mm

   
   
   

   2. 0.40 mm

   
   
   

   3. 0.53 mm

   
   
   

   4. 450 microns

   
   
   

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1. View Hint View Answer Discuss in Forum

   β' =	β	=	0.4	= 0.3 mm
   	μ		4/3

   Correct Option: A

   β' =	β	=	0.4	= 0.3 mm
   	μ		4/3

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20. Two Polaroids P₁ and P₂ are placed with their axis perpendicular to each other. Un polarised light I₀ is incident on P₁. A third Polaroid P₃ is kept in between P₁ and P₂ such that its axis makes an angle 45° with that of P₁ . The intensity of transmitted light through P₂ is

1. 1. 	I0
      	4

   
   
   

   2. 	I0
      	8

   
   
   

   3. 	I0
      	16

   
   
   

   4. 	I0
      	2

   
   
   

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1. View Hint View Answer Discuss in Forum

   
   According to malus law, I = I₀cos² θ
   

   I1 =	I0
   	2

   
   

   I2 =	I0	cos245°
   	2

   
   

   	I0	×	I	=	I0
   	2		2		4

   
   

   I3 =	I0	cos245°
   	4

   
   

   I3 =	I0
   	8

   Correct Option: B

   
   According to malus law, I = I₀cos² θ
   

   I1 =	I0
   	2

   
   

   I2 =	I0	cos245°
   	2

   
   

   	I0	×	I	=	I0
   	2		2		4

   
   

   I3 =	I0	cos245°
   	4

   
   

   I3 =	I0
   	8

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