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Wave Theory of Light — NEET Physics MCQs with Solutions
Free NEET Physics Wave Theory of Light MCQs with step-by-step solutions covering Newton's Corpuscular Theory, Maxwell's Electromagnetic Theory, Max Planck's Quantum Theory, Huygens' Wave Theory, Polarisation of Light, Doppler Effect in 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. Tiny, weightless, perfectly elastic particles (corpuscles) travelling in straight lines ✓ Correct
B. Transverse electromagnetic waves
C. Discrete energy packets called photons
D. Longitudinal mechanical waves in a medium
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. Reflection and rectilinear propagation of light ✓ Correct
B. Polarisation of light
C. Interference of light
D. Diffraction of light
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 longitudinal mechanical wave
B. A stream of photons only
C. A transverse electromagnetic wave ✓ Correct
D. A stream of corpuscles
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. Mutually perpendicular to one another ✓ Correct
B. E parallel to B, both perpendicular to propagation
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. Thomas Young
C. James Clerk Maxwell
D. Heinrich Hertz ✓ Correct
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 as transverse waves
B. Only by moving corpuscles
C. In discrete packets called quanta (photons) ✓ Correct
D. Continuously in any amount
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. $E = h\nu^2$
B. $E = h\nu$ ✓ Correct
C. $E = \nu/h$
D. $E = h/\nu$
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. Infinite
B. Equal to the mass of an electron
C. Zero ✓ Correct
D. h/c
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. A single ray of light
B. The direction in which light travels
C. The path difference between two waves
D. The locus of all points of a medium vibrating in the same phase ✓ Correct
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. Source of secondary wavelets, and the new wavefront is their forward envelope ✓ Correct
B. Source that reflects the wave backward
C. Point that absorbs the wave
D. Fixed point with no further propagation
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. Cylindrical
B. Spherical ✓ Correct
C. Elliptical
D. Plane
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. Parallel to the wavefront
C. Perpendicular to the wavefront ✓ Correct
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. 2π/3
B. π
C. π/2
D. Zero ✓ Correct
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 amplitude only
B. Constant phase ✓ Correct
C. Zero intensity
D. Constant speed only
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. Both transverse and longitudinal
B. Longitudinal
C. Neither
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. Confined to a single plane
B. Along the direction of propagation
C. Absent
D. In all directions perpendicular to the direction of propagation ✓ Correct
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. Rotating randomly
C. Along the direction of propagation
D. Confined to a single plane containing the direction of propagation ✓ Correct
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. Of a particular colour
B. Along the direction of propagation
C. Perpendicular to its transmission axis
D. Parallel to its transmission (pass) axis ✓ Correct
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. $I = I_0 \cos\theta$
B. $I = I_0 \cos^2\theta$ ✓ Correct
C. $I = I_0 \tan^2\theta$
D. $I = I_0 \sin^2\theta$
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. One quarter of the incident
B. Half of the incident
C. Maximum
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. $\sin\theta_B = n$
B. $\cot\theta_B = n$
C. $\tan\theta_B = n$ ✓ Correct
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. Decreases (blue shift)
C. Increases (red shift) ✓ Correct
D. Becomes zero
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. Stationary
C. Rotating about its axis
D. Approaching the observer ✓ Correct
Solution: A blue shift (decrease in wavelength) means the source is approaching, so light is shifted towards higher frequency.
Q26 — Newton's Corpuscular Theory · medium · theory
To explain refraction of light into a denser medium, Newton's corpuscular theory required that the speed of light in the denser medium be:
A. Greater than in the rarer medium ✓ Correct
B. Less than in the rarer medium
C. Zero
D. Equal to that in the rarer medium
Solution: Newton assumed corpuscles are attracted towards the denser medium, increasing their velocity — so light should travel faster in a denser medium. This prediction was later proved wrong.
Q27 — Newton's Corpuscular Theory · medium · theory
The prediction of Newton's corpuscular theory that light travels faster in a denser medium was experimentally disproved by:
A. Foucault's measurement of the speed of light in water ✓ Correct
B. Young's double-slit experiment
C. Millikan's oil-drop experiment
D. Hertz's experiment
Solution: Foucault showed that light travels slower in water (denser) than in air, contradicting the corpuscular prediction and supporting the wave theory.
Q28 — Newton's Corpuscular Theory · medium · theory
In Newton's corpuscular theory, the different colours of light were attributed to:
A. Different frequencies of vibration
B. Different numbers of photons
C. Different wavelengths of a wave
D. Corpuscles of different sizes ✓ Correct
Solution: Newton explained colour by proposing that corpuscles of different sizes produce the sensation of different colours.
Q29 — Newton's Corpuscular Theory · medium · theory
Which phenomenon CANNOT be explained by the corpuscular theory of light?
A. Rectilinear propagation
B. Reflection
C. Interference ✓ Correct
D. Formation of shadows
Solution: Interference (and diffraction and polarisation) are wave phenomena that the particle-based corpuscular theory cannot account for.
Q30 — Newton's Corpuscular Theory · medium · theory
A strong point in favour of Newton's corpuscular theory in his time was that it easily explained:
A. The bending of light around small obstacles
B. The polarisation of reflected light
C. The coloured fringes in thin films
D. Why light travels in straight lines and casts sharp shadows ✓ Correct
Solution: Particles travelling in straight lines naturally explain rectilinear propagation and sharp shadows, which is why the theory was widely accepted for a long time.