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Wave Optics — JEE Main Physics MCQs with Solutions
Free JEE Main Physics Wave Optics MCQs with step-by-step solutions covering Interference, Newton's Corpuscular Theory, Diffraction, Huygen's Principle and Interference of Light, Maxwell's Electromagnetic Theory, Diffraction and Polarisation of Light. Practise online on Prepizo — no login needed.
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Sample questions with solutions
Q1 — Newton's Corpuscular Theory · easy · theory
According to Newton's corpuscular theory, light consists of:
A. Discrete energy packets called photons
B. Longitudinal mechanical waves in a medium
C. Tiny, weightless, perfectly elastic particles (corpuscles) travelling in straight lines ✓ Correct
D. Transverse electromagnetic waves
Solution: Newton proposed that a luminous body emits streams of minute, elastic corpuscles that travel in straight lines at high speed.
Q2 — Newton's Corpuscular Theory · easy · theory
Newton's corpuscular theory could satisfactorily explain:
A. Polarisation of light
B. Interference of light
C. Diffraction of light
D. Reflection and rectilinear propagation of light ✓ Correct
Solution: The corpuscular theory explained rectilinear propagation and reflection (as elastic rebound), but failed for interference, diffraction and polarisation.
Q3 — Maxwell's Electromagnetic Theory · easy · theory
According to Maxwell's electromagnetic theory, light is:
A. A stream of corpuscles
B. A transverse electromagnetic wave ✓ Correct
C. A stream of photons only
D. A longitudinal mechanical wave
Solution: Maxwell showed that light is a transverse electromagnetic wave consisting of oscillating electric and magnetic fields.
Q4 — Maxwell's Electromagnetic Theory · easy · theory
In an electromagnetic wave, the electric field (E), magnetic field (B) and direction of propagation are:
A. E parallel to B, both perpendicular to propagation
B. Mutually perpendicular to one another ✓ Correct
C. E and B along the direction of propagation
D. All parallel to one another
Solution: E, B and the direction of propagation form a mutually perpendicular right-handed set; E and B oscillate in phase.
Q5 — Maxwell's Electromagnetic Theory · easy · theory
Electromagnetic waves were first experimentally produced and detected by:
A. Augustin Fresnel
B. James Clerk Maxwell
C. Heinrich Hertz ✓ Correct
D. Thomas Young
Solution: Heinrich Hertz experimentally generated and detected electromagnetic waves, confirming Maxwell's theoretical prediction.
Q6 — Max Planck's Quantum Theory · easy · theory
According to Planck's quantum theory, light energy is emitted or absorbed:
A. Only by moving corpuscles
B. Only as transverse waves
C. Continuously in any amount
D. In discrete packets called quanta (photons) ✓ Correct
Solution: Planck proposed that radiant energy is emitted or absorbed only in discrete packets (quanta), each of energy E = hν.
Q7 — Max Planck's Quantum Theory · easy · theory
The energy of a single photon (quantum) of light of frequency ν is:
A. $E = h/\nu$
B. $E = h\nu^2$
C. $E = h\nu$ ✓ Correct
D. $E = \nu/h$
Solution: The energy of a photon is E = hν, where h is Planck's constant.
Q8 — Max Planck's Quantum Theory · easy · theory
The rest mass of a photon is:
A. h/c
B. Infinite
C. Equal to the mass of an electron
D. Zero ✓ Correct
Solution: A photon has zero rest mass; it always moves at speed c and carries energy hν and momentum h/λ.
Q9 — Huygens' Wave Theory · easy · theory
A wavefront is defined as:
A. The locus of all points of a medium vibrating in the same phase ✓ Correct
B. A single ray of light
C. The direction in which light travels
D. The path difference between two waves
Solution: A wavefront is the continuous locus of all points that are in the same phase of vibration at a given instant.
Q10 — Huygens' Wave Theory · easy · theory
Huygens' principle states that every point on a wavefront acts as a:
A. Fixed point with no further propagation
B. Point that absorbs the wave
C. Source of secondary wavelets, and the new wavefront is their forward envelope ✓ Correct
D. Source that reflects the wave backward
Solution: Each point on a wavefront is a source of secondary spherical wavelets; the tangential surface (forward envelope) of these wavelets gives the new wavefront.
Q11 — Huygens' Wave Theory · easy · theory
The wavefront produced by a point source of light in an isotropic medium is:
A. Spherical ✓ Correct
B. Elliptical
C. Plane
D. Cylindrical
Solution: A point source sends out wavelets equally in all directions, giving a spherical wavefront.
Q12 — Huygens' Wave Theory · easy · theory
The direction of propagation of light (a ray) is always:
A. At 45° to the wavefront
B. Perpendicular to the wavefront ✓ Correct
C. Parallel to the wavefront
D. Along the wavefront
Solution: A ray points in the direction of energy flow, which is always perpendicular (normal) to the wavefront.
Q13 — Huygens' Wave Theory · easy · theory
Two points lying on the same wavefront have a phase difference of:
A. Zero ✓ Correct
B. π/2
C. 2π/3
D. π
Solution: All points on a wavefront vibrate in the same phase, so the phase difference between any two of them is zero.
Q14 — Huygens' Wave Theory · easy · theory
The physical significance of a wavefront is that it is a surface of:
A. Constant speed only
B. Constant amplitude only
C. Constant phase ✓ Correct
D. Zero intensity
Solution: A wavefront is a surface over which the phase of the wave is constant at a given instant.
Q15 — Polarisation of Light · easy · theory
The phenomenon of polarisation of light establishes that light waves are:
A. Longitudinal
B. Neither
C. Both transverse and longitudinal
D. Transverse ✓ Correct
Solution: Only transverse waves can be polarised; the polarisation of light proves that light is a transverse wave.
Q16 — Polarisation of Light · easy · theory
In an unpolarised light beam, the vibrations of the electric field are:
A. Along the direction of propagation
B. Absent
C. In all directions perpendicular to the direction of propagation ✓ Correct
D. Confined to a single plane
Solution: Unpolarised light has electric-field vibrations in all directions in the plane perpendicular to the direction of propagation.
Q17 — Polarisation of Light · easy · theory
Plane (linearly) polarised light is light in which the vibrations are:
A. In all directions
B. Confined to a single plane containing the direction of propagation ✓ Correct
C. Rotating randomly
D. Along the direction of propagation
Solution: In plane-polarised light the electric-field vibrations are restricted to one plane.
Q18 — Polarisation of Light · easy · theory
A polaroid transmits only those vibrations that are:
A. Perpendicular to its transmission axis
B. Along the direction of propagation
C. Parallel to its transmission (pass) axis ✓ Correct
D. Of a particular colour
Solution: A polaroid selectively transmits the component of vibration parallel to its transmission axis and absorbs the perpendicular component.
Q19 — Polarisation of Light · easy · theory
Malus's law for the intensity of light transmitted by an analyser is:
A. $I = I_0 \tan^2\theta$
B. $I = I_0 \sin^2\theta$
C. $I = I_0 \cos\theta$
D. $I = I_0 \cos^2\theta$ ✓ Correct
Solution: Malus's law: the intensity transmitted by an analyser is I = I₀cos²θ, where θ is the angle between the transmission axes of the polariser and analyser.
Q20 — Polarisation of Light · easy · theory
Two polaroids are crossed (their transmission axes at 90°). The intensity of light emerging from the second polaroid is:
A. Half of the incident
B. Maximum
C. One quarter of the incident
D. Zero ✓ Correct
Solution: At θ = 90°, cos²90° = 0, so no light is transmitted — crossed polaroids block the light.
Q21 — Polarisation of Light · easy · theory
When unpolarised light is reflected at the polarising (Brewster) angle, the reflected light is:
A. Unpolarised
B. Partially polarised only
C. Completely plane-polarised ✓ Correct
D. Circularly polarised
Solution: At the Brewster (polarising) angle, the reflected beam is completely plane-polarised, with vibrations perpendicular to the plane of incidence.
Q22 — Polarisation of Light · easy · theory
Brewster's law relates the polarising angle θ_B to the refractive index n of the medium as:
A. $\tan\theta_B = n$ ✓ Correct
B. $\sin\theta_B = n$
C. $\cot\theta_B = n$
D. $\cos\theta_B = n$
Solution: Brewster's law: the refractive index equals the tangent of the polarising angle, n = tanθ_B.
Q23 — Doppler Effect in Light · easy · theory
The Doppler effect in light is the apparent change in the _____ of light due to relative motion between the source and the observer.
A. Frequency (and wavelength) ✓ Correct
B. Speed
C. Amplitude
D. Direction of polarisation
Solution: Relative motion between source and observer changes the observed frequency and wavelength of light — the Doppler effect.
Q24 — Doppler Effect in Light · easy · theory
When a light source moves away from an observer, the observed wavelength:
A. Stays the same
B. Becomes zero
C. Increases (red shift) ✓ Correct
D. Decreases (blue shift)
Solution: A receding source produces a red shift — the observed wavelength increases (frequency decreases).
Q25 — Doppler Effect in Light · easy · theory
A blue shift in the spectrum of a star indicates that the star is:
A. Receding from the observer
B. Approaching the observer ✓ Correct
C. Stationary
D. Rotating about its axis
Solution: A blue shift (decrease in wavelength) means the source is approaching, so light is shifted towards higher frequency.
Q26 — Interference · easy · theory
The phenomenon of interference of light is based on the principle of:
A. Quantisation of energy
B. Superposition of waves ✓ Correct
C. Rectilinear propagation
D. Total internal reflection
Solution: Interference results from the superposition of two (or more) coherent light waves.
Q27 — Interference · easy · theory
Two sources of light are said to be coherent if they have:
A. Different frequencies
B. The same frequency and a constant phase difference ✓ Correct
C. The same amplitude only
D. A randomly varying phase difference
Solution: Coherent sources emit waves of the same frequency with a constant (time-independent) phase difference.
Q28 — Interference · easy · theory
For constructive interference at a point, the path difference between the two waves must be:
A. $n\lambda/2$
B. $(2n-1)\lambda/2$
C. $n\lambda$ (n = 0, 1, 2, …) ✓ Correct
D. $(2n+1)\lambda/4$
Solution: Constructive interference (bright fringe) occurs when the path difference is an integral multiple of the wavelength, nλ.
Q29 — Interference · easy · theory
For destructive interference, the path difference between the two waves must be:
A. $(2n-1)\dfrac{\lambda}{2}$ ✓ Correct
B. $n\lambda/4$
C. $2n\lambda$
D. $n\lambda$
Solution: Destructive interference (dark fringe) occurs when the path difference is an odd multiple of λ/2.
Q30 — Interference · easy · theory
In Young's double-slit experiment, the fringe width β is given by:
A. $\beta = \dfrac{D d}{\lambda}$
B. $\beta = \dfrac{\lambda}{D d}$
C. $\beta = \dfrac{\lambda d}{D}$
D. $\beta = \dfrac{\lambda D}{d}$ ✓ Correct
Solution: Fringe width β = λD/d, where D is the slit-to-screen distance and d the slit separation.