61. Two coherent sources produce waves of different intensities which interfere. After interference, the ratio of the maximum intensity to the minimum intensity is 16. The intensity of the waves are in the ratio:
A
16 : 9
B
25 : 9
C
4 : 1
D
5 : 3
Answer :
25 : 9
62. A mixture of light, consisting of wavelength $$590\,nm$$ and an unknown wavelength, illuminates Young’s double slit and gives rise to two overlapping interference patterns on the screen. The central maximum of both lights coincide. Further, it is observed that the third bright fringe of known light coincides with the $${4^{th}}$$ bright fringe of the unknown light. From this data, the wavelength of the unknown light is:
A
$$885.0\,nm$$
B
$$442.5\,nm$$
C
$$776.8\,nm$$
D
$$393.4\,nm$$
Answer :
$$442.5\,nm$$
63. The maximum number of possible interference maxima for slit separation equal to $$1.8\lambda ,$$ where $$\lambda $$ is the wavelength of light used, in a Young’s double slit experiment is
A
zero
B
3
C
infinite
D
5
Answer :
3
64. The first diffraction minimum due to the single slit diffraction is seen at $$\theta = {30^ \circ }$$ for a light of wavelength $$5000\,\mathop {\text{A}}\limits^ \circ $$ falling perpendicularly on the slit. The width of the slit is
A
$$2.5 \times {10^{ - 5}}cm$$
B
$$1.25 \times {10^{ - 5}}cm$$
C
$$10 \times {10^{ - 5}}cm$$
D
$$5 \times {10^{ - 5}}cm$$
Answer :
$$10 \times {10^{ - 5}}cm$$
65. In Young’s double-slit experiment, the separation between the slits is halved and the distance between the slits and the screen is doubled. The fringe width is
A
unchanged.
B
halved
C
doubled
D
quadrupled
Answer :
quadrupled
66.
An initially parallel cylindrical beam travels in a medium of refractive index $$\mu \left( I \right) = {\mu _0} + {\mu _2}I,$$ where $${\mu _0}$$ and $${\mu _2}$$ are positive constants and $$I$$ is the intensity of the light beam. The intensity of the beam is decreasing with increasing radius.
The speed of light in the medium is
A
minimum on the axis of the beam
B
the same everywhere in the beam
C
directly proportional to the intensity $$I$$
D
maximum on the axis of the beam
Answer :
minimum on the axis of the beam
67. Two polaroids have their polarizing directions parallel so that the intensity of a transmitted light is maximum. The angle through which either polaroid must be turned if the intensity is to drop by one-half is
A
$${135^ \circ }$$
B
$${90^ \circ }$$
C
$${120^ \circ }$$
D
$${180^ \circ }$$
Answer :
$${135^ \circ }$$
68. Interference fringes were produced using white light in a double slit arrangement. When a mica sheet of uniform thickness of refractive index 1.6 (relative to air) is placed in the path of light from one of the slits, the central fringe moves through some a distance. This distance is equal to the width of 30 interference bands if light of wavelength $$4800\,\mathop {\text{A}}\limits^ \circ $$ is used. The thickness (in $$\mu m$$ ) of mica is
A
90
B
12
C
14
D
24
Answer :
24
69. The angle substanded by the first diffraction minimum for a point source viewed in the hydrogen line at $$1420\,MHz$$ with a radio telescope having an aperture of $$25\,m$$ is:
A
$${0.8^ \circ }$$
B
$${0.64^ \circ }$$
C
$${1.2^ \circ }$$
D
$${2.2^ \circ }$$
Answer :
$${1.2^ \circ }$$
70.
A narrow monochromatic beam of light of intensity $$I$$ is incident on a glass plate as shown in figure. Another identical glass plate is kept close to the first one and parallel to it. Each glass plate reflects 25 per cent of the light incident on it and transmits the remaining. Find the ratio of the minimum and the maximum intensities in the interference pattern formed by the two beams obtained after one reflection at each plate.
A
$$1:30$$
B
$$1:49$$
C
$$1:51$$
D
$$1:73$$
Answer :
$$1:49$$