20.4. Magnetic fields due to currents
A subsection of Physics, 9702, through 20. Magnetic fields
Listing 10 of 37 questions
State Faraday’s law of electromagnetic induction. An alternating current is passed through an air-cored solenoid. An iron core is inserted into the solenoid and then held stationary within the solenoid. The current in the solenoid is now smaller. Explain why the root-mean-square (r.m.s.) value of the current in the solenoid is reduced as a result of inserting the core. Practical transformers are very efficient. However, there are some power losses. State two sources of power loss within a transformer. 1. 2.
9702_w16_qp_42
THEORY
2016
Paper 4, Variant 2
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The diagram shows a length of track from a model railway connected to a battery, a resistor and a relay coil. railway track resistor relay coil With no train present, there is a current in the relay coil which operates a switch to turn on a light. When a train occupies the section of track, most of the current flows through the wheels and axles of the train in preference to the relay coil. The switch in the relay turns off the light. Why is a resistor placed between the battery and the track?
9702_s13_qp_13
MCQ
2013
Paper 1, Variant 3
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A stiff wire is held horizontally between the poles of a magnet, as illustrated in . S N stiff wire When a constant current of 6.0 A is passed through the wire, there is an additional downwards force on the magnet of 0.080 N. On , draw an arrow on the wire to show the direction of the current in the wire. Explain your answer. The constant current of 6.0 A is now replaced by a low-frequency sinusoidal current. The root-mean-square (r.m.s.) value of this current is 2.5 A. Calculate the difference between the maximum and the minimum forces now acting on the magnet. difference = N
9702_w16_qp_42
THEORY
2016
Paper 4, Variant 2
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Questions Discovered
37