**pdf AIR and DD Model Question Papers 2019.**

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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