83 free MCQs on Wave Optics, each with its own worked answer and explanation. Huygens principle, Young's double slit, diffraction, polarization. Essential for JEE.
Take the timed Wave Optics chapterwise test →83 practice questions on Wave Optics, sorted Easy → Hard. Try each one first, then open its answer page for the worked explanation. Want the full theory first? Read the Wave Optics notes.
Two coherent slits S₁ and S₂ act as secondary sources; at each point on the screen, the path difference between light from S₁ and S₂ determines whether the waves arrive in phase (bright fringe) or out of phase (dark fringe), producing the characteristic alternating fringe pattern.
Q1.
The spreading of light into the geometrical shadow region behind an obstacle is called:
Q2.
Two independent light bulbs cannot act as coherent sources because the phase difference between them:
Q3.
In Young double-slit experiment, using light of larger wavelength makes the fringe width:
Q4.
Sound waves cannot be polarised because they are:
Q5.
A point source of light placed at the focus of a convex lens produces a:
Q6.
Huygens' principle states that every point on a wavefront acts as a source of:
Q7.
In Young's double slit experiment, bright fringes occur when the path difference is:
Q8.
Fringe width in YDSE is given by β = λD/d. Increasing the slit separation d will:
Q9.
Polarization of light proves that light is a:
Q10.
Which phenomenon cannot be explained by the wave theory of light?
Q11.
Malus's law states that when polarized light of intensity I<sub>0</sub> passes through an analyser at angle θ:
Q12.
When unpolarized light of intensity I<sub>0</sub> passes through a single polaroid, the transmitted intensity is:
Q13.
Coherent sources must have:
Q14.
In YDSE, the central bright fringe is located at:
Q15.
Diffraction of light is most prominent when the obstacle size is:
Q16.
The Brewster angle for glass (n = 1.5) is approximately:
Q17.
In a single slit diffraction pattern, the first minimum occurs at:
Q18.
Which colour of light has the longest wavelength?
Q19.
The path difference for the 3rd dark fringe from the centre in YDSE is:
Q20.
When a YDSE is submerged in a liquid of refractive index n, the fringe width:
Q21.
Diffraction grating produces a spectrum because:
Q22.
Newton's rings are formed due to:
Q23.
If the distance between slits in YDSE is doubled (other factors constant), the number of fringes visible in the same region:
Q24.
For the condition of destructive interference, path difference must equal:
Q25.
The resolving power of a telescope depends on:
Q26.
In a Young double-slit experiment d = 0.5 mm, D = 1 m and λ = 500 nm. The distance of the third bright fringe from the central maximum is:
Q27.
A thin transparent sheet (μ = 1.6, thickness 2 μm) is placed over one slit in a double-slit setup using λ = 600 nm. The central fringe shifts by:
Q28.
Plane polarised light of intensity I<sub>0</sub> falls on an analyser whose axis is at 30° to the polarisation direction. The transmitted intensity is:
Q29.
Light reflected from the surface of a transparent medium is found to be completely plane polarised at an angle of incidence of 60°. The refractive index of the medium is:
Q30.
In YDSE with slit separation d = 0.5 mm, screen at D = 1 m, λ = 500 nm. What is the fringe width?
Q31.
If the 5th bright fringe in YDSE is at 2.5 mm from centre with D = 1 m and d = 1 mm, what is the wavelength?
Q32.
In YDSE, if one slit is covered, the fringe pattern:
Q33.
Polarized light of intensity I<sub>0</sub> passes through two polaroids with angle θ = 60° between them. Final transmitted intensity is:
Q34.
The central maximum in single slit diffraction is:
Q35.
In a thin film of thickness t and refractive index n, the condition for constructive interference (reflected light) when light is incident from air is:
Q36.
In YDSE, when a mica sheet of thickness t and refractive index μ is placed in front of one slit, the central fringe shifts toward:
Q37.
If a diffraction grating has 500 lines per mm, what is the grating element d?
Q38.
Unpolarized light (I<sub>0</sub>) passes through polaroid P<sub>1</sub>, then through P<sub>2</sub> at 30° to P<sub>1</sub>, then through P<sub>3</sub> at 90° to P<sub>1</sub>. Final intensity is:
Q39.
The angular position of second-order maximum for a diffraction grating with d = 2μm and λ = 500 nm is:
Q40.
The Rayleigh criterion for the limit of resolution of a telescope (objective diameter D) is:
Q41.
In YDSE, what happens to the fringe pattern when white light is used instead of monochromatic light?
Q42.
A glass plate of thickness 0.5 mm and μ = 1.5 is placed in the path of one beam in YDSE (λ = 600 nm). By how many fringes does the pattern shift?
Q43.
At what angle does polarization by reflection (Brewster angle) occur for water (n = 1.33)?
Q44.
In the double slit experiment, the intensity at a point where the path difference is λ/4 is (I<sub>0</sub> = intensity at central max):
Q45.
Interference fringes in Young's experiment have visibility (contrast). Visibility is maximum when:
Q46.
What is the maximum number of orders visible for a grating with d = 3λ?
Q47.
The wavefront of a point source at large distance becomes approximately:
Q48.
In Lloyd's mirror experiment, the fringe pattern is similar to YDSE but the central fringe is:
Q49.
If the slit width in single-slit diffraction is halved, the central maximum width:
Q50.
In a two-slit interference pattern the intensity at the central maximum is I<sub>0</sub>. At a point where the path difference is λ/3, the intensity is:
Q51.
Two coherent sources of intensity I and 9I interfere. The ratio of maximum to minimum intensity in the pattern is:
Q52.
A telescope objective has diameter 5 cm and is used with light of wavelength 550 nm. Its limit of angular resolution is about:
Q53.
In a double-slit experiment light of 480 nm and 600 nm illuminates the slits together. The bright fringes first coincide at:
Q54.
The minimum thickness of a soap film (n = 1.33) that appears bright in reflected light for λ = 532 nm is:
Q55.
A diffraction grating has 6000 lines per cm and is used with light of wavelength 589 nm. The maximum order of the spectrum observable is:
Q56.
In YDSE, the ratio of intensities at maxima and minima is 9:1. What is the ratio of amplitudes of the two sources?
Q57.
In YDSE, slits are separated by d, screen at D. A point source is placed at distance D from the slits, off-axis by y<sub>0</sub>. The central fringe shifts by:
Q58.
Light of wavelengths 400 nm and 600 nm is used in YDSE. What is the minimum distance from centre where fringes coincide?
Q59.
In a diffraction grating, for the n-th order spectrum of wavelength λ_1 to overlap with the (n+1)-th order of λ_2, we need:
Q60.
A thin soap film (t = 400 nm, n = 1.33) is illuminated by white light. Which wavelength of reflected light is most intensified?
Q61.
In YDSE, the n-th dark fringe from centre is at distance y from centre. If the screen moves farther, what happens to y?
Q62.
The resolving power of a diffraction grating with N total slits in order n is:
Q63.
Two coherent waves I<sub>1</sub> = 4I and I<sub>2</sub> = I interfere. The maximum and minimum intensities are:
Q64.
In single-slit diffraction, the intensity at angle θ from centre follows I = I<sub>0</sub> (sinα/α)² where α = πa sinθ/λ. At what value of α is the first secondary maximum approximately?
Q65.
A Michelson interferometer moves one mirror by 0.1 mm. If 200 fringes pass the reference, what is the wavelength?
Q66.
In YDSE with glass slabs of thickness t<sub>1</sub> and t<sub>2</sub> and refractive indices n<sub>1</sub> and n<sub>2</sub> placed in front of slits, the shift of central fringe is:
Q67.
The condition for maximum intensity in Newton's rings (dark central spot) is that the n-th bright ring has radius:
Q68.
Two slits separated by 0.2 mm are illuminated by coherent light of 600 nm. A screen is 1.5 m away. The number of bright fringes between the two direct beams from the slits is approximately:
Q69.
When a biprism (Fresnel biprism) is used in optics, the two virtual coherent sources are created by:
Q70.
The angular width of the central maximum in single-slit diffraction doubles when:
Q71.
In YDSE, if the distance between slits is increased 4 times while the distance to screen is halved, by what factor does fringe width change?
Q72.
What is the minimum thickness of a glass film (n=1.5) that appears dark in reflected light for λ = 600 nm?
Q73.
In a diffraction grating experiment, the 4th order for λ = 500 nm and the n-th order for λ = 625 nm coincide. Find n.
Q74.
The path difference between two waves at a point is 2.5λ. The phase difference is:
Q75.
The coherence length of light is the path difference over which interference can be observed. For sodium light (Δλ = 0.6 nm, λ = 589 nm), the coherence length is approximately:
Q76.
In a Young double-slit experiment, λ = 600 nm, slit separation 1 mm, and screen distance 1 m. The fringe width is:
Q77.
In a double-slit experiment, if the screen distance is doubled (other things fixed), the fringe width:
Q78.
In a two-slit interference pattern, the condition for a bright fringe (constructive interference) is a path difference of:
Q79.
For single-slit diffraction of a slit of width a, the first minimum occurs at an angle satisfying:
Q80.
A Young double-slit apparatus is immersed in water (n = 1.33). Compared with air, the fringe width:
Q81.
Two waves of amplitudes a and 2a interfere. The ratio of maximum to minimum intensity is:
Q82.
For sustained interference, the two light sources must be:
Q83.
The phenomenon of polarization of light establishes that light is a:
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