4.5.5. The d.c. motor
A subsection of Physics, 0625, through 4. Electricity and magnetism
Listing 10 of 62 questions
shows a diagram of an electrical device. The diagram is not complete. The coil rotates in a magnetic field when connected to a d.c. power supply. magnet coil X Y N S Explain the meaning of the term d.c. Complete the diagram in by drawing the symbols for two cells in series and a switch to make a circuit. State the name of the electrical device shown in . State two changes to the electrical device that will make the coil in the device rotate faster. 1. 2.
0625_w19_qp_33
THEORY
2019
Paper 3, Variant 3
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A magnet and a coil are attached separately to a door and a door frame as shown in . The purpose of the arrangement is to activate a circuit connected to an LED indicator when the door is opening or closing. This will provide a visual indication that the door is being used. N S magnet coil door indicator door frame Initially, the door is closed and then it is opened. Explain why the indicator comes on and then goes off when the door is opened. The door shuts. The indicator comes on more brightly but for a shorter time than it did in . Suggest and explain why this happens. A circuit breaker is recommended for use with an electric lawnmower. State two reasons for this recommendation. reason 1 reason 2
0625_w19_qp_43
THEORY
2019
Paper 4, Variant 3
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A transformer has 500 turns on the primary coil and 25 turns on the secondary coil. The input voltage is 120 V. Calculate the output voltage. output voltage = The current in the primary coil is 125 mA. The transformer is 100% efficient. Calculate the output current. output current = shows a loose wire connected in a circuit with a d.c. (direct current) power supply and a switch. The length of the wire between the two supports is in the magnetic field of a horseshoe magnet. N S d.c. power supply switch magnet support support The power supply is switched on and the wire moves down. On , draw an arrow on the wire to show the direction of the current. The power supply is switched off and the wire returns to its original position. The power supply is then switched on so that the current is in the opposite direction. State and explain what happens to the wire. A split-ring commutator is an important feature of a d.c. motor. Suggest one reason why the d.c. motor cannot operate without a split-ring commutator.
0625_w21_qp_43
THEORY
2021
Paper 4, Variant 3
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shows the single turn coil of a simple direct current (d.c.) motor. S O current coil N Explain the direction of the turning effect as seen by an observer at O. The coil is replaced by an otherwise identical new coil with three turns and the same current in the coil. State how the turning effect compares with the turning effect in . A third coil is identical to the coil in except that its resistance is three times greater. The potential difference (p.d.) across the coil is the same as the p.d. in . State how the turning effect compares with the turning effect in . is a voltage–time graph showing the output of a simple alternating current (a.c.) generator at times t0, t1, t2 and t3. t0 t1 t2 t3 voltage time is an end view of the plane of the coil of the generator at time t0. The coil is rotating clockwise. axis of rotation A B Draw an end view of the position of the plane of the coil at time t1. Include the labels A and B. Draw an end view of the position of the plane of the coil at time t2. Include the labels A and B. Draw an end view of the position of the plane of the coil at time t3. Include the labels A and B.
0625_w23_qp_43
THEORY
2023
Paper 4, Variant 3
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Questions Discovered
62