Wave Optics | Physics JEE previous year questions with Solutions

Q 11 :

Given below are two statements. One is labelled as Assertion (A) and the other is labelled as Reason (R)

Assertion (A) : In Young's double slit experiment, the fringes produced by red light are closer as compared to those produced by blue light.

Reason (R) : The fringe width is directly proportional to the wavelength of light.

In the light of above statements, choose the correct answer from the options given below: [2025]

Both (A) and (R) are true and (R) is the correct explanation of (A).
(A) is false but (R) is true.
Both (A) and (R) are true but (R) is NOT the correct explanation of (A)
(A) is true but (R) is false.

1

2

3

4

(2)

$β = \frac{λ D}{d}$

$λ_{red} < λ_{blue}$

Assertion is false

Reason is true

Q 12 :

Given below are two statements: One is labelled as Assertion (A) and the other is labelled as Reason (R)

Assertion (A) : If Young's double slit experiment is performed in an optically denser medium than air, then the consecutive fringes come closer.

Reason (R) : The speed of light reduces in an optically denser medium than air while its frequency does not change.

In the light of the above statements, choose the most appropriate answer from the options given below: [2025]

Both (A) and (R) are true and (R) is the correct explanation of (A)
(A) is false but (R) is true.
Both (A) and (R) are true but (R) is NOT the correct explanation of (A)
(A) is true but (R) is false.

1

2

3

4

(1)

Fringe with $β = \frac{λ D}{d}$

Also, $v = \frac{c}{μ}$ frequency remains same

$\Rightarrow λ_{med} = \frac{λ_{vac}}{μ}$

Hence, $β$ decreases $\Rightarrow$ fringe come closer

Q 13 :

The Young's double slit interference experiment is performed using light consisting of 480 nm and 600 nm wavelengths to form interference patterns. The least number of the bright fringes of 480 nm light that are required for the first coincidence with the bright fringes formed by 600 nm light is [2025]

4
8
6
5

1

2

3

4

(4)

Fringe width of $λ_{1}$ = 480 nm

$β_{1} = \frac{λ_{1} D}{d} = 480 (\frac{D}{d})$

Similarly fringe width for $λ_{2}$ = 600 nm

$β_{2} = λ_{2} (\frac{D}{d}) = 600 (\frac{D}{d})$

Clearly we can see that for minimum value

$5 (β_{1}) = 4 (β_{2})$

That means $5^{th}$ maxima of $λ_{1}$ = 480 nm

coincides with $4^{th}$ maxima of $λ_{2}$ = 600 nm

Q 14 :

Young's double slit interference apparatus is immersed in a liquid of refractive index 1.44. It has slit separation of 1.5 mm. The slits are illuminated by a parallel beam of light whose wavelength in air in 690 nm. The fringe-width on a screen placed behind the plane of slits at a distance of 0.72 m, will be: [2025]

0.23 mm
0.33 mm
0.63 mm
0.46 mm

1

2

3

4

(1)

$β = (\frac{λ_{0}}{μ}) \times \frac{D}{d} = \frac{690 \times 10^{- 9} \times 0.72}{1.44 \times 1.5 \times 10^{- 3}} = 0.23 mm$

Q 15 :

In a Young's double slit experiment, the slits are separated by 0.2 mm. If the slits separation is increased to 0.4 mm, the percentage change of the fringe width is: [2025]

0%
100%
50%
25%

1

2

3

4

(3)

$β_{1} = \frac{λ D}{d}$

$β_{2} = \frac{λ D}{2 d} = \frac{β_{1}}{2}$

%change = 50%

Q 16 :

In a Young's double slit experiment, the source is white light. One of the slits is covered by red filter and another by a green filter. In this case [2025]

There shall be an interference pattern for red distinct from that for green.
There shall be no interference fringes.
There shall be alternate interference fringes of red and green.
There shall be an interference pattern, where each fringe's pattern center is green and outer edges is red.

1

2

3

4

(2)

Q 17 :

A double slit interference experiment performed with a light of wavelength 600 nm forms an interference fringe pattern on a screen with 10th bright fringe having its centre at a distance of 10 mm from the central maximum. Distance of the centre of the same 10th bright fringe from the central maximum when the source of light is replaced by another source of wavelength 660 nm would be ________ mm. [2025]

0%

(11)

In case of YDSE the distance of $n^{th}$ maxima from central maxima is given by

$y = \frac{n λ D}{d}$

Here n, D and d are same,

$\Rightarrow \frac{y_{10}^{'}}{y_{10}} = \frac{λ'}{λ}$

or $y_{10}^{'} = \frac{λ'}{λ} y_{10} = (\frac{660 nm}{600 nm}) 10 mm = 11 mm$

Q 18 :

In a Young's double slit experiment, two slits are located 1.5 mm apart. The distance of screen from slits is 2 m and the wavelength of the source is 400 nm. If the 20 maxima of the double slit pattern are contained within the centre maximum of the single slit diffraction pattern, then the width of each slit is $x \times 10^{- 3}$ cm, where x-value is ________. [2025]

0%

(15)

$\frac{20 λ D}{d} = \frac{2 λ D}{a} \Rightarrow \frac{10}{d} = \frac{1}{a}$

$\Rightarrow a = \frac{d}{10} = \frac{1.5 \times 10^{- 1}}{10} cm = 15 \times 10^{- 3} cm$

Value of x is 15.

Topic Question Set

Q 15 :

In a Young's double slit experiment, the slits are separated by 0.2 mm. If the slits separation is increased to 0.4 mm, the percentage change of the fringe width is: [2025]

Q 16 :

In a Young's double slit experiment, the source is white light. One of the slits is covered by red filter and another by a green filter. In this case [2025]

0%

0%

Want Us to Email you About Special Offers & Updates?