In a physics demonstration, an insulated copper wire is placed directly above a magnetic compass needle, parallel to its north-south alignment. When an electric current is switched on in the wire, the compass needle deflects. Which of the following options correctly explains why this deflection occurs, and describes what happens to the compass needle when the direction of the current is reversed?
Explanation: There is a magnetic field inside the wire.
Effect of reversing current: The compass needle deflects in the opposite direction.
Explanation: There is a magnetic field around the wire.
Effect of reversing current: The compass needle deflects in the opposite direction.
Explanation: There is a magnetic field inside the wire.
Effect of reversing current: The compass needle remains deflected in the same direction.
Explanation: There is a magnetic field around the wire.
Effect of reversing current: The compass needle remains deflected in the same direction.
275 exam-style questions on CIE IGCSE Physics 4.5 Electromagnetic effects, covering 4.5.1a Electromagnetic induction, 4.5.1b Direction of an induced e.m.f., 4.5.2 The a.c. generator, 4.5.3a Magnetic effect of a current and its applications, 4.5.3b Strength and direction of the field around wires and solenoids, 4.5.4a Force on a current-carrying conductor, 4.5.4b Force on beams of charged particles, 4.5.5 The d.c. motor, 4.5.6a Construction and operation of a transformer, 4.5.6b Turns ratio and current in a transformer, and 4.5.6c High-voltage transmission of electricity. Each one has a worked solution and a mark scheme showing where the marks go.