NEET PhysicsUpdated 19 Oct 2026

Wave Optics: NEET PYQs and weightage

Wave Optics carries 3.4 of 100 Physics marks in NEET by past-paper share: 26 of the 758 tagged NEET Physics PYQs in the ViJEEta bank (NEET 2013–2026). It ranks 13 of 30 Physics chapters.

Take the 25-question Wave Optics test Formula sheet ↓All NEET Physics chapters

3.4/100 Weight in Physics

Exam importance (3/5, by past-paper share)

26 NEET PYQs

325 Practice questions

313 With measured difficulty

How the weight is computed: this chapter's tagged NEET PYQs divided by all tagged NEET Physics PYQs in the bank (26 of 758), times 100, with repeated questions counted once. The bank does not store the year of each NEET question, so none is printed. Computed from the bank at build time. Updated 19 Oct 2026.

Wave Optics: formula sheet for NEET

14 formulas, each with when to use it. Copy it onto one page of your notebook: that page is this chapter's handbook.

Fringe width (YDSE)
$β = \frac{λ D}{d}$
Use it when: you need the gap between two neighbouring bright (or dark) fringes; put $λ$ , $D$ , $d$ all in metres
nth bright fringe (YDSE)
$x_{n} = \frac{nλ D}{d} (n = 0, \pm 1, \pm 2, \dots)$
Use it when: asked how far the $n$ th bright fringe sits from the central bright fringe
nth dark fringe (YDSE)
$x_{n} = (n + \frac{1}{2}) \frac{λ D}{d} (n = 0, \pm 1, \pm 2, \dots)$
Use it when: asked where a dark fringe lies on the screen
Path difference at a screen point
$Δ = S_{1} P \sim S_{2} P = \frac{x d}{D}$
Use it when: you know the position $x$ on the screen and want the path difference there
Bright / dark condition
$Δ = nλ (bright)$
$Δ = (n + \frac{1}{2}) λ (dark) (n = 0, 1, 2, \dots)$
Use it when: deciding whether a given path difference gives a maximum or a minimum
Phase difference from path difference
$ϕ = \frac{2 π}{λ} Δ$
Use it when: converting path to phase; $Δ = λ$ means $ϕ = 2 π$ , $Δ = λ /2$ means $ϕ = π$
Resultant intensity (two equal coherent sources)
$I = 4 I_{0} cos^{2} \frac{ϕ}{2}$
Use it when: finding intensity at a point for a given phase difference; $I_{m a x} = 4 I_{0}$ , $I_{m i n} = 0$
Incoherent sources
$I = 2 I_{0} (at every point)$
Use it when: the sources have no fixed phase relation (two separate lamps), so the intensities just add
Single slit minima
$θ \approx \frac{nλ}{a} (n = \pm 1, \pm 2, \pm 3, \dots)$
Use it when: finding the angles of zero intensity in single-slit diffraction
Single slit secondary maxima
$θ \approx (n + \frac{1}{2}) \frac{λ}{a}$
Use it when: locating the weaker bright bands beside the central maximum
Malus' law
$I = I_{0} cos^{2} θ$
Use it when: already polarised light of intensity $I_{0}$ meets a polaroid whose pass-axis is at $θ$ to it
Unpolarised light through one polaroid
$I = \frac{I _{0}}{2}$
Use it when: natural light hits the first polaroid; the result does not change as you rotate it
Polaroid between two crossed polaroids
$I = \frac{I _{0}}{4} sin^{2} 2 θ$
Use it when: three polaroids, outer two crossed; $I_{0}$ is the intensity after the first, maximum at $θ = π /4$
Refraction by Huygens
$\frac{sin i}{sin r} = \frac{v _{1}}{v _{2}} = \frac{λ _{1}}{λ _{2}} = \frac{n _{2}}{n _{1}}$
$n = \frac{c}{v}$
Use it when: light enters a new medium; speed and wavelength change, frequency stays the same

Trap

In single-slit diffraction, θ = nλ/a gives a DARK band, the opposite of YDSE, where path difference nλ gives a BRIGHT fringe. Students swap the two conditions.

How does NEET ask Wave Optics?

8 real previous-year questions from this chapter, as printed in the paper, each with its worked solution. Answer the first one here with no sign-in.

Q1PhysicsNEET UG PYQInterference of Light Waves

Try right here · No sign-in

In Young’s double slit experiment, the slits are 2 mm apart and are illuminated by photons of two wavelength

λ_{1} = 12000 A^{\circ}

and

λ_{2} = 10000 A^{\circ}

. At what minimum distance from the common central bright fringe on the screen 2 m from the slit will a bright fringe from one interference pattern coincide with a bright fringe from the other?

Answer key (B) & worked solution

Correct answer: Option B

For a bright fringe, the width formula is

y = \frac{nλ d}{d}

∴ \frac{n _{1} λ _{1} D}{d} = \frac{n _{2} λ _{2} D}{d}

\to \frac{n _{1}}{n _{2}} = \frac{λ _{2}}{λ _{1}} = \frac{10000 A ^{\circ}}{12000 A ^{\circ}} = \frac{5}{6}

∴ n_{1} = 5 an d n_{2} = 6

\to y = \frac{n _{1} λ _{1} D}{d} = \frac{5 \times 12000 \times 10 ^{- 10} \times 2}{2 \times 10 ^{- 3}}

∴ y = 6 \times 1 0^{- 3} m = 6 mm

Q2PhysicsNEET UG PYQInterference of Light Waves

In interference and diffraction, the light energy is redistributed. If it reduces in one region, producing a dark fringe, it increases in another region, producing a bright fringe. A. As there is no gain or loss of energy, these phenomena are consistent with the principle of conservation of energy. B. Diffraction and interference are characteristics exhibited only by light waves. Choose the correct answer from the options given below:

A

is true, but

B

is false

A

is true and

B

is also true

A

is false, but

B

is true

DBoth

A

and

B

are false

Answer key (A) & worked solution

Correct answer: Option A

In interference and diffraction there is no loss of energy, the energy gets redistributed. Interference and diffraction both are exhibited in light as well as sound waves.

Q3PhysicsNEET UG PYQInterference of Light Waves

In Young's double slit experiment the separation d between the slits is 2 mm, the wavelength λ of the light used is

5896 A \circ

and distance D between the screen and slits is 100 cm. It is found that the angular width of the fringes is

0.2 0^{o}

. To increase the fringe angular width to

0.2 1^{o}

(with same λ and D) the separation between the slits needs to be changed to

A2.1 mm

B1.9 mm

C1.8 mm

D1.7 mm

Answer key (B) & worked solution

Correct answer: Option B

Angular width

= \frac{λ}{d}

0.2 0^{\circ} = \frac{λ}{2 mm}

… (i)

0.2 1^{\circ} = \frac{λ}{d}

… (ii) Dividing we get,

\frac{0.20}{0.21} = \frac{d}{2 mm}

∴ d = 1.9 mm

Q4PhysicsNEET UG PYQPolarization

An unpolarized light beam travelling in air is incident on a medium of refractive index 1.73 at Brewster’s angle. Then -

ABoth reflected and transmitted light are perfectly polarized with angles of reflection and refraction close to

6 0^{\circ}

and

3 0^{\circ}

, respectively

BTransmitted light is completely polarized with angle of refraction close to

3 0^{\circ}

CReflected light is completely polarized and the angle of reflection is close to

6 0^{\circ}

DReflected light is partially polarized and the angle of reflection is close to

3 0^{\circ}

Answer key (C) & worked solution

Correct answer: Option C

μ = 1.73

μ = tan θ_{B}

∴ θ_{B} = tan^{- 1} (1.73)

= tan^{- 1} (3)

= tan^{- 1} (tan 6 0^{\circ})

θ_{B} = 6 0^{\circ}

Reflected light ray should be completely polorised.

θ_{B} =

angle of incident There,

θ_{B} =

angle of incidence

∴

angle of reflection

= θ_{B} = 6 0^{\circ}

∴ 1 \times sin θ_{B} = μ sin r

\Rightarrow sin (6 0^{\circ}) = 3 \times sin r

\Rightarrow \frac{3}{2} = 3 sin r

∴ r = 3 0^{\circ}

(angle of refraction).

\to

Transmitted light in partially polorised.

Q5PhysicsNEET UG PYQInterference of Light Waves

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 the monochromatic source is replaced by another monochromatic source of larger wavelength, the angular separation of fringes decreases. In the light of the above statements, choose the correct answer from the options given below :

ABoth Statement I and Statement II are false

BStatement I is true but Statement II is false

CStatement I is false but Statement II is true

DBoth Statement I and Statement II are true

Answer key (B) & worked solution

Correct answer: Option B

Angular width,

θ_{w} = \frac{λ}{d}

θ_{w}

independent of D but depends on

λ

Q6PhysicsNEET UG PYQInterference of Light Waves

In a double slit experiment, when light of wavelength 400 nm was used, the angular width of the first minima formed on a screen placed 1 m away was found to be 0.2°. What will be the angular width of the first minima, if the entire experimental apparatus is immersed in water?

(μ_{w a t er} = 4/3)

A0.15°

B0.05°

C0.1°

D0.266°

Answer key (A) & worked solution

Correct answer: Option A

In air angular fringe width is given by

θ_{0} = \frac{β}{D}

Angular fringe width in water,

θ_{w} = \frac{β}{μ D} = \frac{θ _{0}}{μ}

= \frac{0. 2 ^{\circ}}{( \frac{4}{3} )} = 0.1 5^{\circ}

Q7PhysicsNEET UG PYQDiffraction

In a diffraction pattern due to a single slit of width ‘a’, the first minimum is observed at an angle 30

^{o}

when light of wavelength 5000

A 0

is incident on the slit. The first secondary maximum is observed at an angle of

sin^{- 1} (\frac{1}{4})

sin^{- 1} (\frac{2}{3})

sin^{- 1} (\frac{1}{2})

sin^{- 1} (\frac{3}{4})

Answer key (D) & worked solution

Correct answer: Option D

For first minima,

sin 3 0^{\circ} = \frac{λ}{a} = \frac{1}{2}

First secondary maxima will be at

sin θ = \frac{3 λ}{2 a} = \frac{3}{2} (\frac{1}{2})

\Rightarrow θ = sin^{- 1} (\frac{3}{4})

Q8PhysicsNEET UG PYQDiffraction

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 either side of the central bright fringe is:

A2.4 cm

B2.4 mm

C1.2 cm

D1.2 mm

Answer key (B) & worked solution

Correct answer: Option B

\frac{2 λ D}{a} = \frac{2 \times 600 \times 10 ^{- 9} \times 2}{10 ^{- 3}} = 2.4 mm

Which topics in Wave Optics carry the most questions?

All 6 topics, by tagged PYQs, then practice questions. Counted from the bank. Updated 19 Oct 2026.

Topic	PYQs	Practice questions
Interference of Light Waves	13	157
Diffraction	7	55
Polarization	6	63
Coherent and Incoherent Addition of Waves	0	30
Huygens Principle	0	18
Miscellaneous Examples	0	2

Why does Wave Optics show "–" until you answer 3 questions?

Unknown is not zero. Until you answer at least 3 graded questions in Wave Optics, ViJEEta shows – instead of a zero or a 50% default. Book exercises can raise chapter mastery up to 0.60, adaptive practice up to 0.75, and only a timed chapter test or mock can certify 0.80 and above.

How ViJEEta scores you

What happens when you test Wave Optics?

Every chapter test is 25 questions. It starts at moderate difficulty and adapts after each saved answer. If you open a solution before answering, that attempt earns no credit, so your mastery stays honest.

Start the Wave Optics test

Chapters either side of Wave Optics by weight

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Wave Optics: NEET PYQs and weightage

Wave Optics: formula sheet for NEET

Fringe width (YDSE)

nth bright fringe (YDSE)

nth dark fringe (YDSE)

Path difference at a screen point

Bright / dark condition

Phase difference from path difference

Resultant intensity (two equal coherent sources)

Incoherent sources

Single slit minima

Single slit secondary maxima

Malus' law

Unpolarised light through one polaroid

Polaroid between two crossed polaroids

Refraction by Huygens

How does NEET ask Wave Optics?

Which topics in Wave Optics carry the most questions?

Why does Wave Optics show "–" until you answer 3 questions?

What happens when you test Wave Optics?

Chapters either side of Wave Optics by weight