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The MCQs below are drawn from the Physics subject category.
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1351
In a bi-prism experiment, if yellow light is replaced by blue light without disturbing the other arrangement, the fringe width will:
A. decrease.
B. remain unchanged.
C. disappear.
D. increase.
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Correct Option
Explanation
Fringe width β = λD/d; replacing yellow by shorter-wavelength blue light decreases λ, so the fringe width decreases.
1352
Polarisation of light proves the:
A. corpuscular nature of light.
B. quantum nature of light.
C. transverse nature of light.
D. longitudinal wave nature of light.
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Correct Option
Explanation
Polarisation is a property that can only occur for transverse waves, so observation of polarization shows light is transverse in nature.
1353
In Young's experiment, monochromatic light is used to illuminate the two slits A and B. A thin glass plate is placed normally in the path of the beam coming from the slit A, then
A. the fringe width will decrease
B. the fringes will disappear
C. there will be no change in fringe width
D. the fringe width will increase
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Correct Option
Explanation
A thin plate introduces a phase shift causing fringe displacement, but fringe width (β = Dλ/d) remains unchanged.
1354
The fact that the edge of a shadow formed by a point source of light shining on an object is not sharp is an example of
A. dispersion
B. polarization
C. diffraction
D. refraction
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Explanation
The blurring of shadow edges is due to diffraction, the bending of waves around edges causing partial illumination.
1355
Conditions for interference are that the two sources should be coherent and:
A. At a far off distance
B. Close together
C. Coinciding
D. None of these
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Explanation
For observable stable interference, the two coherent sources must be close together so that path difference is well-defined across the screen.
1356
When a biprism experiment is performed in water in place of air, the fringe width will
A. remain same
B. increase
C. decrease
D. none
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Correct Option
Explanation
In a medium of higher refractive index the wavelength decreases, so fringe width β ∝ λ decreases; hence fringe width decreases (option B).
1357
A slit of width 'a' is illuminated by white light. The first minimum for red light (λ = 6500 Å) will fall at θ = 30° when 'a' will be:
A. 3250 Å.
B. 1.3 micron.
C. 2.6 × 10^-? cm.
D. 6.5 × 10^-? cm.
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Correct Option
Explanation
For first minimum a sinθ = λ, so a = λ/sin30° = 6500 Å / 0.5 = 13000 Å = 1.3 × 10^-6 m = 1.3 micron.
1358
Sin θ = 0.5 for first order maximum in a diffraction grating. θ is equal to:
A. 30°
B. 3°
C. 15°
D. 60°
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Correct Option
Explanation
If sin θ = 0.5 then θ = 30° as sin 30° = 0.5.
1359
A thin slice is cut out of a glass cylinder along a plane parallel to its axis. The slice is placed on a flat glass plate. The observed interference fringes from this combination shall be
A. circular
B. straight
C. equally spaced
D. having fringe spacing which increases as we go outwards
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Explanation
This is the Newton's rings type arrangement (curved surface on flat plate) producing concentric circular fringes.
1360
Soap film in sunlight appears coloured due to
A. diffraction of light
B. interference of light
C. dispersion of light
D. scattering of light
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Correct Option
Explanation
Colors in thin soap films result from interference between light reflected from the front and back surfaces of the film.
