NEET Optics PYQs | 2013–2025

2025

Q1. Derive the mirror equation for a concave mirror and define the sign conventions.

Q2. A thin convex lens of focal length f = 20 cm forms a real image 30 cm from the lens. Find the object distance.

Q3. Explain total internal reflection and give two practical applications.

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2024

Q1. State and derive the lens maker’s formula.

Q2. A ray of light passes from air to glass (n = 1.5). Calculate the critical angle for total internal reflection.

Q3. Explain the phenomenon of dispersion and its effect in a prism.

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2023

Q1. Derive the magnification formula for a lens and a mirror.

Q2. A converging lens forms a virtual image of a real object. Describe the conditions for this.

Q3. Explain why a rainbow shows different colors and the role of refraction and reflection.

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2022

Q1. Derive the expression for the focal length of a combination of two thin lenses in contact.

Q2. A concave mirror forms an image twice the size of the object. Find the object distance in terms of the focal length.

Q3. Explain the working of a simple microscope and the role of angular magnification.

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2021

Q1. Derive the expression for interference fringes in Young’s double-slit experiment.

Q2. Explain diffraction of light at a single slit and derive the condition for minima.

Q3. Discuss the polarization of light by reflection and Brewster’s angle.

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2020

Q1. Derive the mirror formula for spherical mirrors.

Q2. A concave lens of focal length 15 cm forms an image 10 cm from the lens. Calculate the object distance.

Q3. Explain the working principle of a telescope and the difference between astronomical and terrestrial telescopes.

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2019

Q1. A prism has a refracting angle of 60° and refractive index 1.5. Find the angle of minimum deviation.

Q2. Derive the lens formula and sign conventions for a convex lens.

Q3. Explain constructive and destructive interference with examples.

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2018

Q1. Derive the expression for the resolving power of a microscope.

Q2. Derive the expression for the angular magnification of a simple telescope.

Q3. Explain chromatic aberration in lenses and how it can be minimized.

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2017

Q1. Explain Huygens’ principle and derive the law of refraction.

Q2. A convex lens forms a real image 3 times the size of the object. Find the object distance in terms of focal length.

Q3. Derive the condition for maxima in interference fringes in Young’s double-slit experiment.

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2016

Q1. Derive the expression for focal length of a convex lens in air using the lens maker’s formula.

Q2. A concave mirror of focal length 20 cm forms a virtual image of an object placed 10 cm in front of it. Find the magnification.

Q3. Explain the formation of a rainbow by a spherical water drop.

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2015

Q1. Derive the mirror and lens formula using geometrical optics.

Q2. Calculate the critical angle for a water–air interface (n = 1.33).

Q3. Explain the diffraction pattern produced by a single slit.

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2014

Q1. A convex lens of focal length 25 cm forms a real image at 50 cm. Find the object distance.

Q2. Explain the dispersion of light by a prism and derive the relation between refractive index and angle of minimum deviation.

Q3. Define polarization of light and describe one method of producing polarized light.

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2013

Q1. Derive the formula for magnification of a concave mirror.

Q2. A thin lens produces an image 3 times the size of the object. Determine the object and image distances.

Q3. Explain why the sky appears blue and the phenomenon of Tyndall scattering.

Optics — Solutions (2025 → 2013)

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2025

Q1. Mirror equation for concave mirror.

Solution:

• Using geometry of the mirror:

$$\frac{1}{f} = \frac{1}{v} + \frac{1}{u}$$f1​=v1​+u1​

• Sign conventions:
  • u: object distance (positive if on the incoming light side)
  • v: image distance (positive if real, negative if virtual)
  • f: focal length (positive for concave, negative for convex)

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Q2. Lens problem: f = 20 cm, v = 30 cm → find u.$$\frac{1}{f} = \frac{1}{v} – \frac{1}{u} \implies \frac{1}{20} = \frac{1}{30} – \frac{1}{u}$$f1​=v1​−u1​⟹201​=301​−u1​

$\frac{1}{u} = \frac{1}{30} – \frac{1}{20} = -\frac{1}{60} \implies u = -60 \text{ cm}$u1​=301​−201​=−601​⟹u=−60 cm

✅ Object is on the same side as image → virtual

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Q3. Total internal reflection (TIR):

• Condition: $n_1 > n_2, \theta_i > \theta_c$n1​>n2​,θi​>θc​
• Critical angle: $\theta_c = \sin^{-1}(n_2/n_1)$θc​=sin−1(n2​/n1​)
• Applications: Optical fibers, prisms in binoculars.

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2024

Q1. Lens maker’s formula:$$\frac{1}{f} = (n – 1) \left( \frac{1}{R_1} – \frac{1}{R_2} \right)$$f1​=(n−1)(R1​1​−R2​1​)

Q2. Air → glass (n = 1.5), critical angle:
$\theta_c = \sin^{-1}(1/1.5) = 41.8^\circ$θc​=sin−1(1/1.5)=41.8∘

Q3. Dispersion: Splitting of white light into colors due to wavelength-dependent refractive index. Prism separates sunlight → spectrum.

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2023

Q1. Magnification: m = \frac{h’}{h} = – \frac{v}{u} \] (for mirror) \[ m = \frac{v}{u} \quad (\text{for lens})

Q2. Converging lens forms virtual image: object distance u < f → image on same side as object, upright, magnified.

Q3. Rainbow colors: Refraction + internal reflection in water droplets → dispersion of sunlight.

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2022

Q1. Two thin lenses in contact:$$\frac{1}{F} = \frac{1}{f_1} + \frac{1}{f_2}$$F1​=f1​1​+f2​1​

Q2. Concave mirror, image 2× size:
$|m| = 2 = \frac{v}{u} \implies v = 2u$∣m∣=2=uv​⟹v=2u
Mirror formula: $\frac{1}{f} = \frac{1}{v} + \frac{1}{u} = \frac{1}{2u} + \frac{1}{u} = \frac{3}{2u} \implies u = \frac{3}{2}f$f1​=v1​+u1​=2u1​+u1​=2u3​⟹u=23​f

Q3. Simple microscope: magnifying glass, angular magnification: $M = 1 + \frac{D}{f}$M=1+fD​, D = least distance of distinct vision.

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2021

Q1. Young’s double slit:$$\beta = \frac{\lambda L}{d} \quad (\text{fringe width})$$β=dλL​(fringe width)

Q2. Single slit diffraction minima:$$a \sin \theta = n \lambda, \quad n = 1, 2, 3 \dots$$asinθ=nλ,n=1,2,3…

Q3. Polarization by reflection: Brewster’s angle: $\tan \theta_B = n_2/n_1$tanθB​=n2​/n1​, reflected light is plane-polarized.

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2020

Q1. Mirror formula: $\frac{1}{v} + \frac{1}{u} = \frac{1}{f}$v1​+u1​=f1​

Q2. Concave lens: f = 15 cm, v = -10 cm (virtual image), lens formula:$$\frac{1}{f} = \frac{1}{v} – \frac{1}{u} \implies \frac{1}{15} = -\frac{1}{10} – \frac{1}{u} \implies u = -6 \text{ cm}$$f1​=v1​−u1​⟹151​=−101​−u1​⟹u=−6 cm

Q3. Telescope: two lenses → objective forms real image, eyepiece magnifies it. Astronomical: inverted image, terrestrial: erect image.

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2019

Q1. Prism, A = 60°, n = 1.5 → minimum deviation Dm:$$n = \frac{\sin \frac{A + D_m}{2}}{\sin \frac{A}{2}} \implies D_m = 41.8^\circ$$n=sin2A​sin2A+Dm​​​⟹Dm​=41.8∘

Q2. Convex lens: $\frac{1}{f} = \frac{1}{v} – \frac{1}{u}$f1​=v1​−u1​

Q3. Constructive interference: path difference = nλ
Destructive: path difference = (n + ½)λ

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2018

Q1. Resolving power of microscope:$$R = \frac{\lambda}{2NA}, \quad NA = n \sin \theta$$R=2NAλ​,NA=nsinθ

Q2. Angular magnification of telescope:$$M = \frac{f_o}{f_e}, \quad f_o = \text{objective focal length}, f_e = \text{eyepiece focal length}$$M=fe​fo​​,fo​=objective focal length,fe​=eyepiece focal length

Q3. Chromatic aberration minimized: Use achromatic doublet (crown + flint lens).

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2017

Q1. Huygens principle → law of refraction: wavefront analysis gives Snell’s law:$$\frac{\sin i}{\sin r} = \frac{v_1}{v_2} = \frac{n_2}{n_1}$$sinrsini​=v2​v1​​=n1​n2​​

Q2. Convex lens, m = 3 → v = 3u, lens formula → u = 0.5f, v = 1.5f

Q3. Young’s experiment maxima: path difference Δ = nλ → bright fringes.

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2016

Q1. Lens maker’s formula: $\frac{1}{f} = (n-1) (\frac{1}{R_1} – \frac{1}{R_2})$f1​=(n−1)(R1​1​−R2​1​)

Q2. Concave mirror, u = 10 cm, f = 20 cm → magnification:$$m = -v/u, \quad v = \frac{fu}{u-f} = -20 \text{ cm}, \quad m = 2$$m=−v/u,v=u−ffu​=−20 cm,m=2

Q3. Rainbow formation: refraction + internal reflection + dispersion in raindrops.

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2015

Q1. Mirror & lens formula: $\frac{1}{v} + \frac{1}{u} = \frac{1}{f}$v1​+u1​=f1​

Q2. Water–air, n = 1.33 → critical angle:
$\theta_c = \sin^{-1} (1/1.33) = 48.75^\circ$θc​=sin−1(1/1.33)=48.75∘

Q3. Single slit diffraction minima: $a \sin \theta = n \lambda$asinθ=nλ

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2014

Q1. Convex lens: f = 25 cm, v = 50 cm → u = 50 cm

Q2. Prism: $n = \frac{\sin \frac{A + D_m}{2}}{\sin \frac{A}{2}}$n=sin2A​sin2A+Dm​​​

Q3. Polarization: light passes through Polaroid → plane-polarized light

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2013

Q1. Concave mirror magnification: $m = -v/u$m=−v/u

Q2. Lens forms image 3× size → m = 3 = v/u → solve for u, v using lens formula

Q3. Sky appears blue → Rayleigh scattering (short wavelengths scattered more)