Physics - Optics Question Paper 1
Exam Duration: 45 Mins Total Questions : 21
If the distance between a point source and screen is made one-third, then intensity of light (I) and the initial intensity of light will be related as
- (a)
\(\frac { { I }_{ 0 } }{ 3 } \)
- (b)
\(I=\frac { { I }_{ 0 } }{ 3 } \)
- (c)
\(I= { { I }_{ 0 } }{ } \)
- (d)
\(I= { 9{ I }_{ 0 } }{ } \)
If luminous- efficiency of alamp is 2 lumen per watt and its luminous intensity is 42 candela, then, power of the lamp is
- (a)
62 W
- (b)
76 W
- (c)
138 W
- (d)
264 W
When light wave suffers reflection at the interface between air and glass, the change of phase in the reflected wave is equal to
- (a)
zero
- (b)
\(\lambda \)/2
- (c)
\(\lambda \)
- (d)
2\(\lambda \)
A lens is placed between a source of light and a wall. It forms images of area A1 and A2 on the wall, for its two different positions. The area of the sources obtained is
- (a)
\(({ A }_{ 1 }+{ A }_{ 2 })/2\)
- (b)
\({ \left[ \frac { 1 }{ { A }_{ 1 } } +\frac { 1 }{ { A }_{ 2 } } \right] }^{ -1 }\quad \)
- (c)
\(\sqrt { { A }_{ 1 }A_{ 2 } } \)
- (d)
\({ \left[ \frac { \sqrt { { A }_{ 1 } } +\sqrt { { A }_{ 2 } } }{ 2 } \right] }^{ 2 }\)
If a lens is cut into two pieces perpendicular to the principal axis and only one part is used, the distance of the image
- (a)
remains the same
- (b)
becomes 1/2 time
- (c)
becomes 2 times
- (d)
is infinite
The speed of a wave in a medium is 760 ms-1. If 3600 waves are passing through a point in the medium in 2 minutes, then its wavelength is-
- (a)
13.8m
- (b)
25.3m
- (c)
41.5m
- (d)
57.2m
The wavelength of light diminishes \(\mu \) times in a medium. A driver from inside water (\(\mu \)=1.33) looks at an object whose natural colour is green. He sees the object as
- (a)
green
- (b)
blue
- (c)
yellow
- (d)
red
A plane glass slab is kept over various coloured letters, the letter which appears least raised is
- (a)
blue
- (b)
violet
- (c)
green
- (d)
red
The velocity of light in glass whose refractive index \(\mu _{ g }\) is 1.5 is 2X108ms-1. In certain liquid , the velocity of light is found to be 2.6X108ms-1. The refractive index \(\mu _{ u }\) of that liquid is
- (a)
1.5
- (b)
1.2
- (c)
1
- (d)
2.1
Light enters at an angle of incidence in a transparent rod of refractive index \(\mu \). For what value of \(\mu \), the light once entered into it will not leave it through its lateral face whatsoever br the value of the angle of incidence?
- (a)
\(\mu >\sqrt { 2 } \)
- (b)
\(\mu =1\)
- (c)
\(\mu =1.1\)
- (d)
\(\mu =1.3\)
The reason for shining of air bubble in water is
- (a)
diffraction of light
- (b)
dispersion of light
- (c)
scattering of light
- (d)
total internal reflection of light
The refractive indices of violet and red light are 1.56 and 1.53 respectively. If angle of prism is 40, the angular dispersion in degrees is
- (a)
1.20
- (b)
2.00
- (c)
0.60
- (d)
0.120
Which of the following colours suffers maximum deviation in a prism?
- (a)
Yellow
- (b)
Blue
- (c)
Green
- (d)
Orange
The focal length of a converging lens is measured for violet, green and red colours. It is respectively fV,fG,fR. We will find that
- (a)
fV=fR
- (b)
fV>fR
- (c)
fV<fR
- (d)
fG=fR
fV and fR are the focal lengths of a convex lens for violet and red light respectively and FV and FR are the focal lengths of a concave lens for violet and red light respectively; then we must have
- (a)
fV
R and FV>FR - (b)
fV
R and FV R - (c)
fV>fR and FV>FR
- (d)
fV>fR and FV
R
An acromatic convergent doublet of two lenses in contact has a power of +3D. The convex lens has power +7D. What is the ratio of dispersive powers of convergent and divergent lenses?
- (a)
3:7
- (b)
4:7
- (c)
7:3
- (d)
7:4
A lens focuses paraxial ray at 11.5 cm. The longitudinal spherical aberration of the lens is
- (a)
0.4 cm
- (b)
0.2 cm
- (c)
zero
- (d)
11.3 cm
The differences between angle of minimum deviation for violet and red rays in the spectrum is 20. If the angle of minimum deviation for the mean colour is 480, the dispersive power of material of the prism is
- (a)
0.0832
- (b)
0.0416
- (c)
24
- (d)
48
If tube length of astronomical telescope is 105 cm and magnifying power is 20 for normal setting, calculate the focal length of objective
- (a)
100 cm
- (b)
10 cm
- (c)
20 cm
- (d)
25 cm
A terrestrial telescope is made by introducing an erecting lens of focal length f between the objective and eyepiece lenses of an astronomical telescope. This causes the length of the telescope tube to increase by an amount equal to
- (a)
f
- (b)
2f
- (c)
3f
- (d)
4f
An astronomical telescope of ten-fold angular magnification has a length of 44 cm. The focal length of the objective is
- (a)
4 cm
- (b)
40 cm
- (c)
44 cm
- (d)
440 cm