Q81. Where should an object be placed in
front of a convex lens to get a real and
enlarged image of the object?
CDS 2021 (II)
A At twice the focal length B At infinity C Between the principal focus and
twice the focal length D Beyond twice the focal length.
Show answer
Correct answer: Between the principal focus and
twice the focal length
Q82. A bus starting from a bus-stand and
moving with uniform acceleration
attains a speed of 20 km/h in 10
minutes. What is its acceleration?
CDS 2021 (II)
A 200 km/h2 B 120 km/h2 C 100 km/h2 D 240 km/h2
Show answer
Correct answer: 120 km/h2
Q83. Refraction of light, as it enters from
one transparent medium to another, is
due to
CDS 2021 (II)
A change in temperature of the media B change in the amplitude of light C change in speed of light D internal property of light
Show answer
Correct answer: change in speed of light
Q84. Who amongst the following is a
pioneer in discovering the heating
effect of electric current? CDS 2021 (I)
A Isaac Newton B Galileo Galilei C James P. Joule D J.J. Thomson
Show answer
Correct answer: James P. Joule
Q85. A non-spherical shining spoon can
generally be considered as a
CDS 2021 (I)
A Spherical mirror B Parabolic mirror C Plane mirror D Lens
Show answer
Correct answer: Parabolic mirror
Q86. Which among the following is true for
propagation of sound waves?
NDA 2021 (II)
A Sound can travel in vacuum and it is
a transverse wave in air. B Sound cannot travel in vacuum and
it is a longitudinal wave in air. C Sound can travel in vacuum and it is
a longitudinal wave in air. D Sound cannot travel in vacuum and
it is a transverse wave in air.
Show answer
Correct answer: Sound cannot travel in vacuum and
it is a longitudinal wave in air.
Q87. Nuclear energy is generated by
NDA 2021 (II)
A nuclear fission and its expression
was proposed by Einstein. B nuclear fission and its expression
was proposed by Rutherford. C nuclear fusion and its expression
was proposed by Bohr. D nuclear fusion and its expression
was proposed by Heisenberg.
Show answer
Correct answer: nuclear fission and its expression
was proposed by Rutherford.
Q88. Power of a lens of focal length 25 cm
is
NDA 2021 (II)
A + 2 5. Dioptre B + 3 Dioptre C + 4 Dioptre D + 5 Dioptre
Show answer
Correct answer: + 4 Dioptre
Q89. ‘Beats’ is a phenomenon that occurs
when frequencies of two harmonic
waves are
NDA 2021 (I)
A equal B far apart C multiples of each other D nearly same
Show answer
Correct answer: nearly same
Q90. Which one of the following cannot be
the unit of frequency of a sound
wave?
NDA 2021 (I)
A dB B s
1
− C Hz D min−1
Show answer
Correct answer: dB
Q91. Twinkling of stars is due to
NDA 2021 (I)
A particular frequencies of the
starlight. B reflection of starlight from the
oceanic surface. C atmospheric refraction of starlight. D magnetic field of earth.
Show answer
Correct answer: atmospheric refraction of starlight.
Q92. Which one of the following
conclusions could not be derived from
Rutherford’s α-particle scattering
experiment?
NDA 2021 (I)
A Most of the space in the atom is
empty. B The radius of the atom is about 105
times the radius of the nucleus. C Electrons move in a circular path of
fixed energy called orbits. D Nearly all the mass of the atom
resides in the nucleus.
Show answer
Correct answer: Electrons move in a circular path of
fixed energy called orbits.
Q93. When light is scattered by a molecule
and the frequency of the scattered
light is changed, this phenomenon is
called
NDA 2021 (I)
A Rayleigh scattering B Raman effect C Photoelectric effect D Rutherford scattering
Show answer
Correct answer: Raman effect
Q94. Which one of the following statements
is not correct for light rays ?
NDA 2021 (I)
A Light travels at different speeds in
different media. B Light travel at almost 300 million
metres per second in air. C Light speeds down as it leaves a
water surface and enters the air. D Light speeds up as it leaves a glass
surface and enters the air.
Show answer
Correct answer: Light speeds down as it leaves a
water surface and enters the air.
Q95. According to the new cartesian sign
convention, which one of the following
is correct in respect of the formula
1
1
1
f
v
u
=
+
, where symbols have their
usual meanings?
NDA 2021 (I)
A It applies only to spherical mirrors. B It applies only to spherical lenses. C It applies to spherical mirrors as well
as spherical lenses. D It is an invalid formula.
Show answer
Correct answer: It applies only to spherical mirrors.
Q96. LED
A semiconductor device) is an
abbreviation that stands for
NDA 2021 (I)
(a) Licence for Energy Detector B Light Energy Device C Light Emitting Diode D Lost Energy Detector
Show answer
Correct answer: Light Emitting Diode
Q97. Consider the following statements
about light year.
NDA 2021 (I)
1. Light year is a unit for measurement
of very large distances.
2. Light year is a unit for measurement
of very large time intervals.
3. Light year is a unit for measurement
of intensity of light.
Which of the statements given above
is/are correct?
A 1, 2 and 3 B 2 and 3 C 1 and 2 D Only 1
Show answer
Correct answer: Only 1
Q98. The power of a lens is + 2.0D. The
focal length of the lens and its nature
are
WBCS 2021
A 50 cm, concave B 50 cm, convex C 100 cm, convex D 100 cm, concave
Show answer
Correct answer: 50 cm, convex
Q99. The solar cooker works on the same
principle as
WBCS 2021
A Bolometer B Pyrometer C Greenhouse D Solar PV cell
Show answer
Correct answer: Greenhouse
Q100. Which of the following is not a unit of
distance?
WBCS 2021
A Light year B Parsec C Furlong D Jiffy
Show answer
Correct answer: Jiffy