How much of JEE Main comes from Optics?

JEEGenie estimates about 6% of JEE Main marks come from Optics, based on recent papers. The share varies from year to year.

Which formulas matter most in Optics?

The Optics sheet on this page has 20 formula entries, starting with Refraction of Light, Critical Angle and Total Internal Reflection (TIR), Mirror Formula, Magnification for Mirrors, Lens Formula. Each one comes with when to use it and the trap to avoid.

What topics does Optics cover for JEE?

Optics covers Reflection and Mirrors, Refraction and Lenses, Total Internal Reflection, Optical Instruments, Interference, Diffraction and Polarisation.

How should I revise Optics before the exam?

Learn each formula together with its condition of use, read the trap listed beside it, then practise questions and review every mistake. The practice link on this page opens Optics questions on JEEGenie.

How many previous-year questions are there on Optics?

JEEGenie has 753 previous-year questions on Optics, and this page shows a few with worked explanations.

Is practice on Optics free on JEEGenie?

Sign-up is free and includes a 7-day Pro trial. After the trial, free accounts keep a limited daily quota.

Optics for JEE Main & Advanced — formulas, what is asked, and traps

JEEGenie estimates about 6% of JEE Main marks come from Optics. This page covers 20 formula entries, each with when to use it, what JEE asks and the traps. A common slip: Confusing angle of incidence with angle between incident ray and surface; it's measured from the normal.

Key points to know

Reflection of Light. Light bounces back into the same medium when it strikes a smooth surface, obeying the laws of reflection.
Refraction of Light. Light bends when passing from one medium to another due to change in speed, governed by Snell's law.
Critical Angle and Total Internal Reflection (TIR). When light travels from a denser to rarer medium at an angle greater than the critical angle, it is completely reflected back.
Power of a Lens. Measure of the lens's ability to converge or diverge light, reciprocal of focal length in meters.
Prism and Angle of Deviation. Light bends through a prism, with deviation depending on angle of incidence and prism angle.
Dispersion of Light. Splitting of white light into its constituent colors due to variation of refractive index with wavelength.
Optical Instruments: Simple Microscope. Uses a single convex lens to magnify objects placed just inside the focal point.
Wave Optics: Huygens' Principle. Every point on a wavefront acts as a source of secondary wavelets, and the new wavefront is the envelope of these wavelets.
Interference of Light. Superposition of two coherent waves produces constructive (bright) or destructive (dark) fringes.
Diffraction of Light. Bending of light around obstacles, producing a pattern of maxima and minima due to interference of wavelets.

Formula sheet

Name	Formula	When to use
Refraction of Light	$n_{1} \sin i = n_{2} \sin r$	Use for any problem involving light crossing a boundary between two media.
Critical Angle and Total Internal Reflection (TIR)	$\sin C = \frac{n_{2}}{n_{1}}$ where $n_{1} > n_{2}$	Use in problems involving optical fibers, mirages, or diamond sparkle.
Mirror Formula	$\frac{1}{f} = \frac{1}{u} + \frac{1}{v}$	Use to find image position or focal length in mirror problems.
Magnification for Mirrors	$m = \frac{h_{i}}{h_{o}} = - \frac{v}{u}$	Use to find image size or orientation in mirror problems.
Lens Formula	$\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$	Use for any thin lens problem involving image formation.
Lens Maker's Formula	$\frac{1}{f} = (n - 1) (\frac{1}{R_{1}} - \frac{1}{R_{2}})$	Use to find focal length of a lens given its geometry and material.
Magnification for Lenses	$m = \frac{h_{i}}{h_{o}} = \frac{v}{u}$	Use to find image size or orientation in lens problems.
Power of a Lens	$P = \frac{1}{f}$ (in meters), unit: diopter (D)	Use in problems involving lens combinations or optometry.
Combination of Lenses (in contact)	$P_{n e t} = P_{1} + P_{2} + P_{3} + . . .$	Use when multiple lenses are placed close together.
Prism and Angle of Deviation	$δ = i + e - A$ (for small angles, $δ = (n - 1) A$ )	Use in problems involving prism geometry and dispersion.
Refractive Index from Prism (Minimum Deviation)	$n = \frac{\sin (\frac{A + δ_{m}}{2})}{\sin (\frac{A}{2})}$	Use to find refractive index of prism material from experimental data.
Dispersion of Light	Angular dispersion = $δ_{v} - δ_{r}$	Use in problems involving rainbows, prisms, or chromatic aberration.
Dispersive Power	$ω = \frac{δ_{v} - δ_{r}}{δ_{y}}$ where $δ_{y}$ is deviation for yellow light	Use to compare dispersive properties of different materials.
Optical Instruments: Simple Microscope	Magnifying power $M = 1 + \frac{D}{f}$ (for final image at near point $D = 25$ cm)	Use in problems on simple magnifiers.
Compound Microscope	Total magnification $M = m_{o} \times m_{e} = (- \frac{L}{f_{o}}) \times (1 + \frac{D}{f_{e}})$ (near point)	Use in problems on compound microscopes.
Astronomical Telescope	Magnifying power $M = - \frac{f_{o}}{f_{e}}$ (for relaxed eye, image at infinity)	Use in problems on astronomical telescopes.
Interference of Light	Path difference $Δ x = n λ$ for maxima, $(2 n + 1) λ / 2$ for minima	Use in Young's double-slit experiment or thin film problems.
Young's Double-Slit Experiment (YDSE)	Fringe width $β = \frac{λ D}{d}$	Use to find fringe spacing or wavelength in YDSE.
Diffraction of Light	For single slit: minima at $a \sin θ = n λ$	Use in problems on single-slit diffraction or resolving power.
Resolving Power of Optical Instruments	For telescope: $θ_{m i n} = 1.22 \frac{λ}{D}$ ; For microscope: $d_{m i n} = \frac{1.22 λ}{2 \sin θ}$	Use in problems on telescopes, microscopes, or human eye resolution.

Open the Optics formula page

What JEE asks

Reflection of Light. JEE often tests the laws of reflection in problems with multiple mirrors or rotating mirrors, requiring angle calculations.
Refraction of Light. JEE frequently combines Snell's law with geometry in prism or lens problems, often requiring critical angle concepts.
Critical Angle and Total Internal Reflection (TIR). JEE often asks for the condition for TIR in prisms or fiber optics, or calculates critical angle from refractive indices.
Mirror Formula. JEE tests this with numerical problems involving magnification or combination of mirrors.
Magnification for Mirrors. JEE often combines magnification with mirror formula to solve for unknown distances.
Lens Formula. JEE tests this with numericals on image formation, often combined with lens maker's formula.
Lens Maker's Formula. JEE often asks to find $f$ when lens is immersed in a different medium or for combinations.
Magnification for Lenses. JEE tests this with problems on magnifying power of simple microscopes.
Sign Convention for Mirrors and Lenses. JEE penalizes sign errors heavily; always draw ray diagram and apply convention consistently.
Power of a Lens. JEE often asks for net power of combination of lenses in contact.
Combination of Lenses (in contact). JEE tests this with numericals on equivalent focal length.
Prism and Angle of Deviation. JEE often asks for refractive index from minimum deviation data.
Refractive Index from Prism (Minimum Deviation). JEE tests this with numericals on prism experiments.
Dispersion of Light. JEE often asks for dispersive power or combination of prisms for achromatism.
Dispersive Power. JEE tests this in problems on achromatic combinations.
Ray Diagrams for Mirrors and Lenses. JEE often asks to identify correct ray diagram from options.
Optical Instruments: Simple Microscope. JEE tests the formula for magnifying power in normal adjustment vs. near point.
Compound Microscope. JEE often asks for magnification or tube length adjustments.
Astronomical Telescope. JEE tests this with numericals on length of telescope ( $f_{o} + f_{e}$ ) and magnification.
Wave Optics: Huygens' Principle. JEE often asks conceptual questions on Huygens' construction.
Interference of Light. JEE tests this with fringe width calculations and intensity distribution.
Young's Double-Slit Experiment (YDSE). JEE often asks for change in $β$ when medium changes or slits are modified.
Diffraction of Light. JEE tests this with angular width of central maximum or Rayleigh criterion.
Resolving Power of Optical Instruments. JEE often asks for minimum angular separation or effect of wavelength.

Common traps

Confusing angle of incidence with angle between incident ray and surface; it's measured from the normal. Reflection of Light
Using degrees in sin calculations without converting to radians when needed; always use degrees in JEE. Refraction of Light
Applying TIR when light goes from rarer to denser; it only occurs from denser to rarer. Critical Angle and Total Internal Reflection (TIR)
Sign convention errors: use Cartesian sign convention (distances measured from pole, positive in direction of incident light). Mirror Formula
Forgetting the negative sign: it indicates image orientation (inverted if negative). Magnification for Mirrors
Sign convention: for convex lens, $f$ is positive; for concave, $f$ is negative. $u$ is negative for real objects. Lens Formula
Sign convention for $R_{1}$ and $R_{2}$ : positive if center of curvature is on the outgoing side. Lens Maker's Formula
No negative sign here (unlike mirrors); sign of $m$ comes from $v$ and $u$ signs. Magnification for Lenses
Applying different conventions for mirrors and lenses; stick to one (Cartesian) for both. Sign Convention for Mirrors and Lenses
Using $f$ in cm; always convert to meters for power in diopters. Power of a Lens
Forgetting sign of each lens's power. Combination of Lenses (in contact)
Using the formula $δ = (n - 1) A$ only for thin prisms (small $A$ ). Prism and Angle of Deviation
Using this formula when deviation is not minimum; it's only valid at $δ_{m}$ . Refractive Index from Prism (Minimum Deviation)
Assuming all colors deviate equally; violet deviates most, red least. Dispersion of Light

Topics in Optics

Reflection and Mirrors
Refraction and Lenses
Total Internal Reflection
Optical Instruments
Interference
Diffraction and Polarisation

Previous-year questions on Optics

JEEGenie has 753 previous-year questions on Optics. A few worked examples follow.

Year	Questions
2026	58
2025	65
2024	50
2023	53
2022	50
2021	53
2020	37
2019	68
2018	17
2017	10
2016	23
2015	16
2014	15
2013	21
2012	14
2011	6
2010	13
2009	7
2008	6
2007	8
2006	6
2005	11
2004	12
2003	8
2002	10
2001	8
2000	10
1999	8
1998	10
1997	9
1996	7
1995	4
1994	4
1993	3
1992	6
1991	3
1990	2
1989	5
1988	3
1987	3
1986	3
1985	5
1984	4
1983	7
1982	3
1981	4
1980	1
1979	2
1978	2

Question 1 easy

For a thin symmetric prism made of glass (refractive index 1.5), the ratio of incident angle and minimum deviation will be _______.

3 : 4
3 : 2
2 : 1
1 : 2

Answer: B

Explanation. For a thin prism, the angle of minimum deviation is

D_{m} = (μ - 1) A .

Given

μ = 1.5

D_{m} = (1.5 - 1) A = 0.5 A = \frac{A}{2} .

At minimum deviation, the ray inside the prism is symmetric, so the angle of refraction at each face is

r = \frac{A}{2} .

Using Snell’s law at the first face for small angles,

i = μ r = 1.5 \times \frac{A}{2} = \frac{3 A}{4} .

Now, the ratio of incident angle to minimum deviation is

\frac{i}{D_{m}} = \frac{\frac{3 A}{4}}{\frac{A}{2}} = \frac{3}{4} \times \frac{2}{1} = \frac{3}{2} .

Thus, the ratio is

3 : 2

B

From NTA/IIT papers: JEE Main 2026 · 2 Apr Shift 1

Question 2 medium

A light wave is propagating with plane wave fronts of the type

x + y + z =

constant. Th angle made by the direction of wave propagation with the

x

-axis is :

$\cos^{- 1} (2 / 3)$
$\cos^{- 1} (\frac{1}{\sqrt{3}})$
$\cos^{- 1} (\frac{1}{3})$
$\cos^{- 1} (\sqrt{\frac{2}{3}})$

Answer: B

Explanation. The wavefront equation is

x + y + z = constant

. The direction of propagation is normal to the wavefront, i.e., along the gradient

\nabla (x + y + z) = (1, 1, 1)

. The direction cosines are proportional to

(1, 1, 1)

. The cosine of the angle

θ

with the

x

-axis is

\cos θ = \frac{1}{\sqrt{1^{2} + 1^{2} + 1^{2}}} = \frac{1}{\sqrt{3}} .

Thus

θ = \cos^{- 1} (\frac{1}{\sqrt{3}})

. The answer is option B.

From NTA/IIT papers: JEE Main 2025 · 2 Apr Shift 1

Question 3 hard

A point source S emits unpolarized light uniformly in all directions. At two points A and B, the ratio

r = I_{A} / I_{B}

of the intensities of light is

2

. If a set of two polaroids having

45^{\circ}

angle between their pass-axes is placed just before point B, then the new value of

r

will be _____.

Answer: 8

Explanation. We have

r = \frac{I_{A}}{I_{B}} = 2.

Since the source is isotropic, intensity falls as

1 / d^{2}

. Thus

\frac{I_{A}}{I_{B}} = \frac{d_{B}^{2}}{d_{A}^{2}} = 2.

When unpolarized light passes through a polaroid, intensity becomes half. After the first polaroid at B:

I_{B 1} = \frac{I_{B}}{2} .

After the second polaroid with angle

45^{\circ}

between pass axes, Malus’s law gives:

I_{B 2} = I_{B 1} \cos^{2} 45^{\circ} = \frac{I_{B}}{2} \cdot \frac{1}{2} = \frac{I_{B}}{4} .

Now the new ratio is

r_{new} = \frac{I_{A}}{I_{B 2}} = \frac{I_{A}}{I_{B} / 4} = 4 \cdot \frac{I_{A}}{I_{B}} = 4 \cdot 2 = 8.

8

From NTA/IIT papers: JEE Advanced 2024

Question 4 easy

A monochromatic light wave with wavelength

λ_{1}

and frequency

v_{1}

in air enters another medium. If the angle of incidence and angle of refraction at the interface are

45^{\circ}

and

30^{\circ}

respectively, then the wavelength

λ_{2}

and frequency

v_{2}

of the refracted wave are:

$λ_{2} = λ_{1}, v_{2} = \frac{1}{\sqrt{2}} v_{1}$
$λ_{2} = λ_{1}, v_{2} = \sqrt{2} v_{1}$
$λ_{2} = \sqrt{2} λ_{1}, v_{2} = v_{1}$
$λ_{2} = \frac{1}{\sqrt{2}} λ_{1}, v_{2} = v_{1}$

Answer: D

Explanation. Frequency remains the same when light refracts. Using Snell's law and the relation between refractive index and wavelength,

λ_{2} = λ_{1} / \sqrt{2}

From NTA/IIT papers: JEE Main 2023 · 6 Apr Shift 1

Question 5 medium

Time taken by light to travel in two different materials

A

and

B

of refractive indices

μ_{A}

and

μ_{B}

of same thickness is

t_{1}

and

t_{2}

respectively. If

t_{2} - t_{1} = 5 \times 10^{- 10}

s and the ratio of

μ_{A}

μ_{B}

1 : 2

. Then, the thickness of material, in meter is: (Given

v_{A}

and

v_{B}

are velocities of light in

A

and

B

materials respectively.)

$5 \times 10^{- 10} v_{A} m$
$5 \times 10^{- 10} m$
$1.5 \times 10^{- 10} m$
$5 \times 10^{- 10} v_{B} m$

Answer: A

Explanation.

t = m u * x / c, t 2 - t 1 = x * (μ 2 - μ 1) / c = 5 e - 10, μ 1 / μ 2 = 1 / 2, μ 2 = 2 * μ 1, x * (2 * μ 1 - μ 1) / c = x * μ 1 / c = 5 e - 10, x = 5 e - 10 * c / μ 1. S i n c e v A = c / μ 1, x = 5 e - 10 * v A

From NTA/IIT papers: JEE Main 2022 · 25 Jul Shift 1

Frequently asked questions

How much of JEE Main comes from Optics?: JEEGenie estimates about 6% of JEE Main marks come from Optics, based on recent papers. The share varies from year to year.
Which formulas matter most in Optics?: The Optics sheet on this page has 20 formula entries, starting with Refraction of Light, Critical Angle and Total Internal Reflection (TIR), Mirror Formula, Magnification for Mirrors, Lens Formula. Each one comes with when to use it and the trap to avoid.
What topics does Optics cover for JEE?: Optics covers Reflection and Mirrors, Refraction and Lenses, Total Internal Reflection, Optical Instruments, Interference, Diffraction and Polarisation.
How should I revise Optics before the exam?: Learn each formula together with its condition of use, read the trap listed beside it, then practise questions and review every mistake. The practice link on this page opens Optics questions on JEEGenie.
How many previous-year questions are there on Optics?: JEEGenie has 753 previous-year questions on Optics, and this page shows a few with worked explanations.
Is practice on Optics free on JEEGenie?: Sign-up is free and includes a 7-day Pro trial. After the trial, free accounts keep a limited daily quota.