Magnetic Effects of Electric Current — Questions & Answers

Sample questions from Magnetic Effects of Electric Current

1. Q1. A coil of 3 turn(s) and area 0.03 m² is placed normally in a magnetic field of 0.4 T. What is N B A?

   • A.0.0360 Wb-turns✓
   • B.3.43 Wb
   • C.13.33 Wb
   • D.1.20 Wb
   Solution

   N B A = 3 × 0.4 × 0.03 = 0.0360 Wb-turns.

2. Q2. In a domestic circuit, an electric fuse is connected

   • A.in parallel with the appliance, in the neutral wire
   • B.in series with the appliance, in the live wire✓
   • C.in parallel with the appliance, in the live wire
   • D.in series with the earth wire
   Solution

   A fuse must carry the whole current, so it is in series, and it is placed in the live wire so that melting it cuts off the live supply.

3. Q3. Trial 7: A coil has 2 turns and carries 3 A. If the current is increased to 4 A with turns unchanged, the magnetic field due to the coil will generally:

   • A.increase✓
   • B.decrease
   • C.become zero
   • D.remain exactly unchanged
   Solution

   For a coil, magnetic field strength increases when current increases, with other factors unchanged.

4. Q4. A coil has 100 turns and carries 0.2 A. If its current is doubled, the product N I becomes:

   • A.40.0 A-turns✓
   • B.20.0 A-turns
   • C.10.0 A-turns
   • D.22.0 A-turns
   Solution

   N is unchanged and I doubles, so NI becomes 100 × 0.4 = 40.0 A-turns.

5. Q5. The split ring in a simple motor mainly: In a second trial, the same principle is tested.

   • A.reverses current every half turn✓
   • B.increases resistance to infinity
   • C.produces the magnetic field alone
   • D.measures the speed
   Solution

   The split ring reverses coil current so torque continues in the same rotational direction.

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