51. The transfer ratio beta of a transistor is 50. The input resistance of the transistor when used in
the common emitter configuration is 1 kOhm. The peak value of the co current for an A.C. input
voltage of 0.01 V peak is ?
(a)100 microA
(b) 0.01 mA
(c)0.25 mA
(d) 500 microA
Ans:d
52. The cause of the potential barrier in a p-n diode is ?
(a) Depletion of positive charges near the junction
(b) Concentration of positive charges near the junction
(c) Depletion of negative charges near the junction
(d) Concentration of positive and negative charges near the junction
Ans:d
53. In forward bias, the width of potential barrier in a p-n junction diode?
(a)increases
(b) decreases
(c) remains constant
(d) first increases then decreases
Ans:b
54. A depletion lay consists of?
(a)electrons
(b) protons
(c)mobile ions
(d) immobile ions
Ans:d
55. Which of the following when added acts as an impurity into silicon produced n-type semi
conductor?
(a)P
(b) Al
(c)B
(d) Mg
Ans:a
56. In a junction diode, the holes are due to
(a) protons
(b) extra electrons
(c) neutrons
(d) missing electrons
Ans:d
57. The intrinsic semiconductor becomes an insulator at
(a)0°C
(b)0K
(c) 300K
(d) —100°C
Ans:b
58. For a common emitter circuit if IC/IE = 0.98 then current gain for common emitter circuit will
be
(a)49
(b)98
(e)4.9
(d) 25.5
Ans:a
59. In a p-n junction
(a) The potential of the p and n sides becomes higher alternately
(b) The p side is at higher electrical potential than the n side
(c) The n side is at higher electrical potential than the p side
(d) Both the p and n sides are at the same potential
Ans:b
60. In the case of a common emitter transistor amplifier the ratio of the collector current to the
emitter current Ic/Ie is 0.96. The current gain of the amplifier is ?
(a)6
(b)48
(c) 24
(d) 12
Ans:c
61. if a full wave rectifier circuit is operating from 5oHz mains, the fundamental frequency in the
tipple will be
(a)100Hz
(b) 25Hz
(c)50Hz
(d) 70.7 Hz
Ans:a
62. A n-p-n transistor conducts when ?
(a) both collector and emitter are negative with respect to, the base
(b) both collector and emitter are positive with respect to the base
(c) collector is positive and emitter is negative with to the base
(d) collector is positive and emitter is at same potential as the base
Ans:c
63. Barrier potential of a p-n junction diode does not depend on?
(a)doping density
(b) diode design
(c)temperature
(d) forward bias
Ans:b
64. Reverse bias applied to a junction diode
(a) increases the minority carrier current
(b) lowers the potential barrier
(c) raises the potential barrier
(d) increases the majority carrier current
Ans:c
65. In semiconductors at a room temperature
(a) the conduction band is completely empty
(b) the valence band is partially empty and the conduction band is partially filled
(c) the valence band is completely filled and the conduction band is partially filled
(d) the valence band is completely filled
Ans:c
66. The output of OR gate is 1 when?
(a) if either input is zero
(b) if both inputs are zero
(c) if either or both inputs are 1
(d) only if both inputs are I
Ans:c
67. In a p-n junction photo cell, the value of the photo-electromotive force produced by
monochromatic light is proportional to ?
(a) the voltage applied at the p-n junction
(b) the barrier voltage at the p-n junction
(c) the intensity of the light falling on the cell
(d) the frequency of the light falling on the cell
Ans:c
68. Choose the only false statement from the following.
(a) in conductors the valence and conduction bands may overlap.
(b) Substances with energy gap of the order of 10 eV are insulators.
(c) The resistivity of a semiconductor increases with increase in temperature.
(d) The conductivity of a semiconductor increases with increase in temperature.
Ans:c
69. Carbon, Silicon and Germanium atoms have four valence electrons each. Their valence and
conduction bands are separated by energy band gaps represented by (Eg)C, (Eg)Si and (Eg)Ge
respectively. Which one of the following relationship is true in their case?
(a) (Eg)C> (Eg)Si
(b) (Eg)C< (Eg)Si
(c) (Eg)C=(Eg)Si
(d) (Eg)C< (Eg)Ge
Ans:a
70. Application of a forward bias to a p—n junction
(a) widens the depletion zone.
(b) increases the potential difference across the depletion zone.
(c) increases the number of donors on the n side.
(d) increases the electric field in the depletion zone.
Ans:c
71. Zener diode is used for?
(a) Amplification
(b) Rectification
(c) Stabilisation
(d) Producing oscillations in an oscillator
Ans:c
72. A current carrying coil is subjected to a uniform magnetic field. The coil will orient so that
its
plane becomes ?
(a) inclined at 45° to the magnetic field
(b) inclined at any arbitrary angle to the
magnetic field
(c) parallel to the magnetic field
(d) perpendicular to magnetic field
Ans:c
73. Tesla is the unit of
(a) magnetic flux
(b) magnetic field
(c) magnetic induction
(d) magnetic moment
Ans:b
74. Energy in a current carrying coil is stored in the
form of ?
(a) electric field
(b) magnetic field
(c) dielectric strength
(d) heat
Ans:b
75. The total charge induced in a conducting loop when it is moved in magnetic field depends
on?
(a) the rate of change of magnetic flux
(b) initial magnetic flux only
(c) the total change in magnetic flux
(d) final magnetic flux only.
Ans:c
76. The magnetic induction at a point P which is at the distance of 4 cm from a long current
carrying wire is 10-3 T. The field of induction at a distance 12 cm from the current will be ?
(a) 3.33 x 10-4 T
(b) 1.11x 10-4 T
(c) 3×10-3 T
(d) 9×10-3 T
Ans:a
77. A charge moving with velocity v in X-direction is subjected to a field of magnetic induction
in negative X-direction. As a result, the charge will
(a) remain unaffected
(b) start moving in a circular path in Y—Z plane
(c) retard along X-axis
(d) moving along a helical path around X-axis
Ans:a
78. A uniform magnetic field acts right angles to the direction of motion of electrons. As a result,
the electron moves in a circular path of radius 2cm. If the speed of electrons is doubled, then the
radius of the circular path will be ?
(a)2.0 cm
(b) 0.5 cm
(c)4.0cm
(d) 1.0cm
Ans:c
79. A deuteron of kinetic energy 50 keV is describing a circular orbit of radius 0.5 metre in a
plane perpendicular to magnetic field B. The kinetic energy of the proton that describes a circular
orbit of radius 0.5 metre in the same plane with
the same B is
(a)25 keV
(b) 50 keV
(c)200 keV
(d) 100 keV
Ans:d
80. A straight wire of length 0.5 metre and carrying a current of 1.2 ampere is placed in uniform
magnetic field of induction 2 Tesla. The magnetic field is perpendicular to the length of the wire.
The force on the wire is ?
(a) 2.4N
(b) 1.2N
(c) 3.0 N
(d) 2.0 N
Ans:b
81. To convert a galvanometer into an ammeter, one needs to connect a ?
(a) low resistance in parallel
(b) high resistance in parallel
(c) low resistance in series
(d) high resistance in series.
Ans:a
82. A coil carrying electric current is placed in uniform magnetic field
(a) torque is formed
(B) e.m.f is induced
(c) both (a) and (b) are correct
(d) none of the above
Ans:a
83. The magnetic field at a distance ‘r’ from a long wire carrying current ‘i’ is 0.4 Tesla. The
magnetic field at a distance ‘2r’ is ?
(a)0.2Tesla
(b) 0.8 Tesla
(c)0.1 Tesla
(d) 1.6 Tesla
Ans:a
84. A electron enters a region where magnetic (B) and electric (E) fields are mutually
perpendicular, then ?
(a) it will always move in the direction of B
(b) it will always move in the direction of E
(c) it always possesses circular motion
(d) it can go un deflected also.
Ans:d
85. A straight wire of diameter 0.5 mm carrying a current of 1 A is replaced by another wire of I
mm diameter carrying same current. The strength of magnetic field far away is?
(a) twice the earlier value
(b) same as the earlier value
(c) one-half of the earlier value
(d) one-quarter of the earlier value
Ans:b
86. At what distance from a long straight wire carrying a current of 12 A will the magnetic field
be equal to 3×10-6 Wb/metre Square
(a) 8×10-2 m
(b) 12×10-2 m
(c)18x 10-2 m
(d) 24×10-2 m
Ans:a
87. An electron moves in a circular orbit with a uniform speed v. It produces a magnetic field B
at the centre of the circle. The radius of the circle is proportional to ?
(a) ?(B/v)
(b) B/v
(c) ?(v/B)
(d)v/B
Ans:d
88. A 10 eV electron is circulating in a plane at right angles to a uniform field at magnetic
induction 10-4 Wb/m2 (= 1.0 gauss). The orbital radius of the electron is ?
(a) 12cm
(b) 16cm
(c) 11cm
(d) 18cm
Ans:c
89. A galvanometer acting as a voltmeter will have?
(a) a low resistance in series with its coil.
(b) a high resistance in parallel with its coil
(c) a high resistance in series with its coil
(d) a low resistance in parallel with its coil
Ans:c
90. A beam of electrons is moving with constant velocity in a region having simultaneous
perpendicular electric and magnetic fields of strength 20 Vm-1 and 0.5 T respectively at right
angles to the direction of motion of the electrons. Then the velocity of electrons must be?
(a) 8m/s
(b) 20 m/s
(c) 40m/s
(d) 1/40 m/s
Ans:c
91. A galvanometer of resistance 20 Ohms gives full scale deflection with a current of 0.004 A.
To convert it into an ammeter of range 1 A, the required shunt resistance should be?
(a) 0.38 Ohms
(b) 0.21 Ohms
(c) 0.08 Ohms
(d) 0.05 Ohms
Ans:c
92. A long solenoid carrying a current produces a magnetic field B along its axis. If the current is
doubled and the number of turns per cm is halved, the new value of the magnetic field is ?
(a) 4B
(b) B/2
(c) B
(d) 2B
Ans:c
93. A positively charged particle moving due east enters a region of uniform magnetic field
directed vertically upwards. The particle will
(a) continue to move due east
(b) move in a circular orbit with its speed unchanged
(c) move in a circular orbit with its speed increased
(d) gets deflected vertically upwards.
Ans:b
94. Two long parallel wires are at a distance of 1 metre. Both of them carry one ampere of
current The force of attraction per unit length between the two wires is?
(a)2 x10-7 N/m
(b) 2 x10-8 N/m
(c) 5×10-8 N/m
(d)10-7 N/m
Ans:a
95. A galvanometer having a resistance of 8 ohms is shunted by a wire of resistance 2 ohms. If
the total current is 1 amp, the part of it passing through the shunt will be?
(a)0.25 amp
(b) 0.8 amp
(c)0.2 amp
(d) 0.5 amp
Ans:b
96. A coil of one turn is made of a wire of certain length and then from the same length a coil of
two turns is made. If the same current is passed in both the cases, then the ratio of the magnetic
inductions at their centres will be?
(a)2:1
(b)1:4
(c)4:1
(d)1:2
Ans:b
97. Magnetic field intensity in the centre of coil of 50 turns, radius 0.5 m and carrying a current
of 2A is ?
(a) 0.5 x 10-5 T
(b) 1.25x 10-4 T
(c) 3x 10-5 T
(c) 4 x 10-5 T
Ans:b
98. When a proton is accelerated through I V, then its kinetic energy will be?
(a)1840 eV
(b) 13.6eV
(c)1 eV
(d) 0.54eV
Ans:c
99. If a long hollow copper pipe carries a current,thin magnetic field is produced
(a)inside the pipe only
(b)outside the pipe only
(c)both inside and outside the pipe
(d) no where
Ans:b
100. A charged particle moves through a magnetic field in a direction perpendicular to it. Then
the
(a) velocity remains unchanged
(b) speed of the particle remains unchanged
(c) direction of the particle remains unchanged
(d) acceleration remains unchanged
Ans:b
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