Wave Optics NEET Questions with Solutions

Q: How many questions come from Wave Optics in NEET 2027?

You can expect 1 to 2 questions in NEET 2027, often with the bigger ask coming from Young's double slit experiment (fringe width, intensity at a point), single-slit diffraction width, and polarisation laws (Brewster's, Malus').

Q: What is a wavefront?

A wavefront is a surface where all points are at the same phase of oscillation. A point source produces a spherical wavefront. Far from a source, the wavefront becomes a plane. The direction perpendicular to the wavefront is the direction of propagation (the ray).

Q: What does Huygens' principle say?

Every point on a wavefront acts as a source of secondary spherical wavelets. The new wavefront at a later time is the envelope of these secondary wavelets. Used to derive reflection (angle equal), refraction (Snell's law follows from speed difference) and propagation in general.

Q: What are coherent sources?

Two sources are coherent if they have the same frequency and a constant phase difference. Coherence is required to see a stable interference pattern. Sunlight from two different filaments is incoherent: the phase between them changes randomly. A laser is highly coherent.

Q: What is the formula for fringe width in YDSE?

beta = lambda D over d, where lambda is wavelength, D is the slit-to-screen distance and d is the separation between the slits. Fringe width is the distance between consecutive bright (or dark) fringes. Same for both. The pattern is periodic with bright at x = n lambda D / d.

Q: How is YDSE pattern modified if a glass slab is placed in front of one slit?

The slab introduces an extra optical path of (n - 1) t, where n is the refractive index of the glass and t is its thickness. The whole fringe pattern shifts towards the side with the slab by (n - 1) t D over d, equivalent to ((n - 1) t / lambda) fringes.

Q: What is the width of the central maximum in single-slit diffraction?

2 lambda D over a, where a is the slit width and D is the slit-to-screen distance. First minima on either side at a sin theta = lambda. The central max is twice as wide as the secondary maxima.

Q: What is the difference between interference and diffraction?

Interference is between coherent waves from two (or more) discrete sources (e.g. two slits). Fringes are equally bright and equally spaced. Diffraction comes from many wavelets across one aperture. Central max is brightest, secondary maxima decrease in brightness, central max is twice the width of the others.

Q: What is Brewster's law and what is special at Brewster's angle?

tan theta_B = n. At this angle of incidence (from the rarer side), the reflected light is completely plane-polarised perpendicular to the plane of incidence. The reflected and refracted rays are exactly 90 degrees apart. Polaroid sunglasses reduce glare from horizontal surfaces (water, road) by blocking this polarised reflection.

Q: What does Malus' law tell us?

When polarised light of intensity I_0 passes through a polariser whose axis makes angle theta with the wave's polarisation direction, the transmitted intensity is I = I_0 cos^2 theta. Crossed polarisers (theta = 90°) block all light. Unpolarised light through an ideal polariser has intensity halved (I_0 / 2).

Question 1

Light with an energy flux of 25 × 10 4 Wm –2 falls on a perfectly reflecting surface at normal incidence. If the surface area is 15 cm 2 , the average force exerted on the surface is

Accepted Answer

2.50 × 10 –6 N

Question 2

A beam of light of λ = 600 nm from a distant source falls on a single slit 1 mm wide and the resulting diffraction pattern is observed on a screen 2m away. The distance between first dark fringes on e

Accepted Answer

2.4 mm

Question 3

In the Young's double-silt experiment, the intensity of light at a point on the screen where the path difference is λ is K, ( λ being the wave length of light used). The intensity at a point where the

Accepted Answer

K/2

Question 4

A jawless fish, which lays eggs in fresh water and whose ammocoetes larvae after metamorphosis return to the ocean is :

Accepted Answer

Petromyzon

Question 5

At the first minimum adjacent to the central maximum of a single-slit diffraction pattern, the phase difference between the Huygen’s wavelet from the edge of the slit and the wavelet from the midpoint

Accepted Answer

π radian

Question 6

In a diffraction pattern due to a single slit of width ‘a’, the first minimum is observed at an angle 30o when light of wavelength 5000 Å is incident on the slit. The first secondary maximum is observ

Accepted Answer

sin−1( 3 4 )

Question 7

The intensity at the maximum in a Young’s double slit experiment is I0. Distance between two slits is d = 5λ, where λ is the wavelength of light used in the experiment. What will be the intensity in f

Accepted Answer

I0 2

Question 8

Young’s double slit experiment is first performed in air and then in a medium other than air. It is found that 8 th bright fringe in the medium lies where 5 th dark fringe lies in air. The refractive

Accepted Answer

1.78

Question 9

Two Polaroids P1 and P2 are placed with their axis perpendicular to each other. Unpolarised light I0 is incident on P1. A third polaroid P3 is kept in between P1 and P2 such that its axis makes an ang

Accepted Answer

0 8 I

Question 10

In Young’s double slit experiment the separation d between the slits is 2 mm, the wavelength λ of the light used is 5896 Å and distance D between the screen and slits is 100 cm. It is found that the a

Accepted Answer

1·9 mm

Question 11

For p-type semiconductor, which of the following statements is true?

Accepted Answer

Holes are the majority carri es and trivalent atoms are the dopants

Question 12

In the circuits shown below, the readings of the voltmeters and the ammeters will be:

Accepted Answer

𝑉1= 𝑉2 and 𝑖1=𝑖2

Question 13

In Young’s double slit experiment, if the separation between coherent sources is halved and the distance of the screen from the coherent sources is doubled, then the fringe width becomes :

Accepted Answer

four times

Question 14

The number of photons per second on an average emitted by the source of monochromatic light of wavelength 600 nm, when it delivers the power of 3.3 × 10 − 3 watt will be : (h = 6.6 × 10 − 34 Js)

Accepted Answer

10 17

Question 15

In a Young’s double slit experiment, a student observes 8 fringes in a certain segment of screen when a monochromatic light of 600 nm wavelength is used. If the wavelength of light is changed to 400 n

Accepted Answer

12

Question 16

For Young’s double slit experiment, two statements are given below:
Statement I: If screen is moved away from the plane of slits, angular separation of the fringes remains constant.
Statement II: If t

Accepted Answer

Statement I is true but Statement II is false.

Question 17

If the monochromatic source in Young’s double slit experiment is replaced by white light, then

Accepted Answer

There will be a central bright white fringe surrounded by a few coloured fringes

Question 18

The intensity of transmitted light when a polaroid sheet, placed between two crossed polaroids at [math] from the polarization axis of one of the polaroids, is ([math] is the intensity of polarised li

Accepted Answer

[math]

Wave OpticsNEET Physics · Class 12 · NCERT Chapter 10

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Wave OpticsNEET Physics · Class 12 · NCERT Chapter 10

1NEET 2014Medium4 bookletsLight with an energy flux of 25 × 10 4 Wm –2 falls on a perfectly reflecting surface at normal incidence. If the surface area is 15 cm 2 , the average force exerted on the surface is

2NEET 2014Medium4 bookletsA beam of light of λ = 600 nm from a distant source falls on a single slit 1 mm wide and the resulting diffraction pattern is observed on a screen 2m away. The distance between first dark fringes on either side of the central bright fringe is :

3NEET 2014Medium4 bookletsIn the Young's double-silt experiment, the intensity of light at a point on the screen where the path difference is λ is K, ( λ being the wave length of light used). The intensity at a point where the path difference is λ /4, will be

4NEET 2015Medium4 bookletsA jawless fish, which lays eggs in fresh water and whose ammocoetes larvae after metamorphosis return to the ocean is :

5NEET 2015Medium4 bookletsAt the first minimum adjacent to the central maximum of a single-slit diffraction pattern, the phase difference between the Huygen’s wavelet from the edge of the slit and the wavelet from the midpoint of the slit is:

6NEET 2016Medium4 bookletsIn a diffraction pattern due to a single slit of width ‘a’, the first minimum is observed at an angle 30o when light of wavelength 5000 Å is incident on the slit. The first secondary maximum is observed at an angle of:

7NEET 2016Medium4 bookletsThe intensity at the maximum in a Young’s double slit experiment is I0. Distance between two slits is d = 5λ, where λ is the wavelength of light used in the experiment. What will be the intensity in front of one of the slits on the screen placed at a distance D =10 d?

8NEET 2017Medium5 bookletsYoung’s double slit experiment is first performed in air and then in a medium other than air. It is found that 8 th bright fringe in the medium lies where 5 th dark fringe lies in air. The refractive index of the medium is nearly

11NEET 2019Medium5 bookletsFor p-type semiconductor, which of the following statements is true?

12NEET 2019Medium4 bookletsIn the circuits shown below, the readings of the voltmeters and the ammeters will be:

13NEET 2020Medium24 bookletsIn Young’s double slit experiment, if the separation between coherent sources is halved and the distance of the screen from the coherent sources is doubled, then the fringe width becomes :

14NEET 2021Medium24 bookletsThe number of photons per second on an average emitted by the source of monochromatic light of wavelength 600 nm, when it delivers the power of 3.3 × 10 − 3 watt will be : (h = 6.6 × 10 − 34 Js)

17NEET 2024Medium24 bookletsIf the monochromatic source in Young’s double slit experiment is replaced by white light, then

18NEET 2025Medium4 bookletsThe intensity of transmitted light when a polaroid sheet, placed between two crossed polaroids at 22.5∘ from the polarization axis of one of the polaroids, is (I0​ is the intensity of polarised light after passing through the first polaroid):

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