Electricity and Magnetic Fundamentals

91. If the resistance of a material 2 m long and 2 m∧2 in area of cross-section is 1.6 X10∧-8 Q, then its resistivity is

  1. 3.2 X 10∧-8 Ω-m
  2. 1.6 X 1O∧-8 Ω-m
  3. 0.64 X 10∧-8 Ω-m
  4. 0.16 X 10∧-8 Ω-m

Correct answer: (B)
1.6 X 1O∧-8 Ω-m

92. If the right handed bottle-opener cork screw is assumed to be along the conductor so as to advance in the direction of current flow, the motion of its handle will indicate the direction of magnetic flux produced around the conductor. This is known as

  1. Right hand rule
  2. Left hand rule
  3. Cork screw rule
  4. End rule

Correct answer: (C)
Cork screw rule

93. If the solenoid is gripped by the right hand with the fingers pointing the direction of current flow, the outstretched thumb will then point the north pole. This is known as

  1. Right hand rule
  2. Helix rule
  3. End rule
  4. Cork screw rule

Correct answer: (B)
Helix rule

94. If the value of α0 a conductor is 1/234 per oC, then the value of α18 is

  1. 1/218 per °C
  2. 1/252 per °C
  3. 1/272 per °C
  4. 1/273 per °C

Correct answer: (B)
1/252 per °C

95. If the value of α25 of a conductor is 1/230 per °C, then the value of a0 is

  1. 1/18O per °C
  2. 1/150 per °C
  3. 1/280 per °C
  4. 1/230 per °C

Correct answer: (A)
1/18O per °C

96. If the value of a25 a conductor is 1/255 per °C, then the value of a20 is

  1. 1/300 per °C
  2. 1/25O per °C
  3. 1/230 per °C
  4. 1/260 per °C

Correct answer: (B)
1/25O per °C

97. If two similar charges 1 coulomb each are placed 1 m apart in air, then the force of repulsion is

  1. 8 X 10∧6 N
  2. X 1O A N
  3. 10∧6 N
  4. 5 X 10∧6 N

Correct answer: (B)
X 1O A N

98. If you hold the conductor with right hand so that the stretched thumb points in the direction of the current, then encircling fingers will give the direction of magnetic lines of force round the conductor. This is known as

  1. Left hand cork screw rule
  2. Right hand cork screw rule
  3. Left hand rule
  4. Right hand rule

Correct answer: (D)
Right hand rule

99. In electro-mechanical conversion devices like generators and motors the reason why a small air gap is left between the rotor and stator is to

  1. permit mechanical clearance
  2. increase flux density in air gap
  3. decrease the reluctance of magnetic path
  4. complete the magnetic path

Correct answer: (A)
permit mechanical clearance

100. It is the reciprocal of reluctance and implies the case of readiness with which magnetic flux is developed.

  1. Resistance
  2. Conductance
  3. Permeance
  4. Inductance

Correct answer: (C)
Permeance

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