4.5.5. The d.c. motor
A subsection of Physics, 0625, through 4. Electricity and magnetism
Listing 10 of 62 questions
A model train uses an electric motor. The motor has a coil of wire in a magnetic field. shows a coil of wire in a magnetic field. S N north pole current coil of wire south pole Describe two ways of increasing the turning effect on the coil. The motor for the model train uses an alternating voltage of 12 V. This is supplied by the secondary coil of a transformer. The primary coil of the transformer is connected to a mains voltage of 240 V. The primary coil has 900 turns. Calculate the number of turns on the secondary coil. number of turns on the secondary coil =
0625_s20_qp_32
THEORY
2020
Paper 3, Variant 2
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shows a simple direct current (d.c.) electric motor. The coil rotates about the axis when there is a current in the coil. The coil is connected to the rest of the circuit by the brushes. + – brush brush coil axis N S On , draw a pair of arrows to show which way the coil rotates. Explain the direction you have chosen. On , draw an arrow to show the direction in which electrons flow through the coil. Explain why the electrons flow in the direction you have shown in . State any difference each of the following changes makes to the rotation of the coil in : changing the polarity of the power supply to that shown in + – changing the coil to the new coil shown in original coil new coil using a stronger magnetic field.
0625_s20_qp_43
THEORY
2020
Paper 4, Variant 3
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A student uses a coil and a magnet on a spring to generate an electromotive force (e.m.f.) that varies. He suspends the magnet above a coil as shown in . N S X to centre-reading voltmeter spring magnet coil The student pulls the magnet through the coil to X and then releases it. The magnet moves up and down through the coil. State the type of voltage induced in the coil. Tick (3) one box. alternating digital direct State two ways of increasing the voltage induced in the coil. 1. 2.
0625_s21_qp_31
THEORY
2021
Paper 3, Variant 1
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shows an electric screwdriver which has an electric motor and a battery. electric motor battery The electric motor has a current-carrying coil in a magnetic field. The screwdriver’s manufacturer decides that the turning effect of the coil is too small. State three ways of increasing the turning effect of the coil. 1. 2. 3. The coil in the motor can rotate in either direction. State what happens in the coil to reverse the direction of rotation. The battery is charged using a transformer connected to an a.c. power supply. The primary voltage Vp to the transformer is 234 V and the secondary voltage Vs of the transformer is 18 V. The number of turns on the primary coil Np is 2470 turns. Calculate the number of turns on the secondary coil Ns. Ns =
0625_s21_qp_32
THEORY
2021
Paper 3, Variant 2
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Two identical radioactive sources emit α-particles and γ-rays into two vacuum tubes. shows two electrically charged plates on either side of one of the vacuum tubes. source initial path of beam of α-particles and γ-rays plate at +2500 V plate at –2500 V vacuum Write the symbol α once in Table 8.1 to indicate any deflection of the α-particles. Write the symbol γ once in Table 8.1 to indicate any deflection of the γ-rays. Table 8.1 into page out of page no deflection towards bottom of page towards top of page shows the poles of a very strong magnet on either side of the other vacuum tube. source initial path of beam of α-particles and γ-rays S pole of strong magnet N pole of strong magnet vacuum S N Write the symbol α once in Table 8.2 to indicate any deflection of the α-particles. Write the symbol γ once in Table 8.2 to indicate any deflection of the γ-rays. Table 8.2 into page out of page no deflection towards bottom of page towards top of page shows a simple direct current (d.c.) electric motor with a split-ring commutator. X coil brush split-ring N S State and explain the direction of rotation of the coil as seen from point X. statement explanation The coil rotates through 90° from the position shown. State what happens to the moment in this position. The coil is rotated through 180° from the position shown. By considering the forces on the coil, explain how the split-ring commutator enables the motor to turn continuously.
0625_s21_qp_42
THEORY
2021
Paper 4, Variant 2
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The coils in two electric motors are identical in size, but motor 1 is observed to spin more quickly than motor 2. Three suggestions are made to explain this observation. The current in the coil of motor 1 is greater than the current in the coil of motor 2. The number of turns on the coil of motor 1 is greater than on the coil of motor 2. The magnets in motor 1 are stronger than the magnets in motor 2. Which suggestions give a possible explanation for this observation?
0625_s22_qp_12
MCQ
2022
Paper 1, Variant 2
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Questions Discovered
62