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1421
1. To demonstrate the phenomenon of interference, we require
A. two sources which emit radiations of different wavelengths
B. two sources which emit radiations of the same frequency and have a definite phase relationship
C. two sources which emit radiations of nearly the same frequency
D. two sources which emit radiations of the same frequency
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Correct Option
Explanation
Interference requires coherent sources: same frequency and a definite phase relationship between them.
1422
The spacing between lines of diffraction grating is:
A. Opaque
B. Transparent
C. Semi-transparent
D. None of these
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Correct Option
Explanation
Gratings consist of opaque rulings separated by transparent spaces (slits), so the spacing between lines is transparent.
1423
The diffraction of light was discovered by
A. Young
B. Newton
C. Hertz
D. Francesco Grimaldi
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Correct Option
Explanation
Francesco Grimaldi first observed and described diffraction effects of light, making him the discoverer.
1424
The path difference 'BD' for destructive interference is
A. (m + 1/2) λ
B. 3λ
C. mλ
D. d sin θ
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Correct Option
Explanation
Destructive interference occurs when path difference = (m + 1/2)λ, so option A is correct.
1425
A calcite crystal is placed over a dot on a piece of paper and rotated. On seeing through the calcite one will see:
A. two stationary dots.
B. one dot rotating about the other.
C. two rotating dots.
D. one dot.
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Correct Option
Explanation
Birefringent calcite produces ordinary and extraordinary images; when rotated one image appears to move relative to the other, so one dot appears to rotate about the other.
1426
In a double slit experiment, instead of taking slits of equal widths, one slit is made twice as wide as the other. Then, in the interference pattern
A. the intensity of the maxima decreases and the minima has zero intensity
B. the intensity of the maxima decreases and that of the minima increases
C. the intensity of the maxima increases and the minima has zero intensity
D. the intensities of both the maxima and the minima increase
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Correct Option
Explanation
Unequal slit widths increase overall amplitudes so maxima intensity increases; minima are no longer zero and thus their intensity also increases compared with the equal-width case (where minima were zero).
1427
On using white light in Fresnel biprism, interference fringes will be
A. width change
B. no change
C. central fringe white and rest of the fringes coloured
D. bright and dark
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Correct Option
Explanation
With white light the central fringe (zero path difference) includes all wavelengths (white), while other fringes show dispersion (coloured), so option B.
1428
The transverse nature of light is shown by:
A. Polarization of light.
B. Interference of light.
C. Dispersion of light.
D. Refraction of light.
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Correct Option
Explanation
Polarization demonstrates that the electric field oscillations are perpendicular to the direction of propagation, indicating transverse wave nature.
1429
Diffraction effect is:
A. More for a round edge
B. More for a sharp edge
C. Less for a sharp edge
D. None of these
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Correct Option
Explanation
A sharp edge produces stronger diffraction because abrupt discontinuities scatter the wave more effectively compared to a smooth rounded edge.
1430
In Young's double slit experiment, the fringe width does not depend upon
A. wavelength (λ)
B. distance between slits (d)
C. ratio Nd
D. distance between slits and screen (D)
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Correct Option
Explanation
Fringe width β = λD/d depends on λ, D, and d, but not on any ratio Nd, so option D is correct.
