4. Electricity and magnetism
A section of Physics, 0625
Listing 10 of 2294 questions
shows a coil of wire rotating steadily in the magnetic field between the poles of a permanent magnet. The current generated in the coil is to pass through resistor R. N S rotation of coil coil A B R D C The apparatus in is part of an a.c. generator. What is connected between the ends A and B of the coil and the connections C and D? On , sketch a graph to show the variation with time of the current through R. current time On , show the time T corresponding to one complete rotation of the coil. State two ways in which the graph would be different if the coil spins at a faster rate. 1. 2. Suggest what could be connected between C and R so that the current in R is always in the same direction.
0625_s14_qp_31
THEORY
2014
Paper 3, Variant 1
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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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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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shows a magnet on the end of a spring and a coil of wire connected to a sensitive centre-zero galvanometer. The magnet can move freely through the coil. spring coil of wire centre-zero galvanometer N S The magnet is pulled down and released. Describe and explain what happens to the needle of the sensitive galvanometer. The magnet is replaced with a stronger magnet. State the effect of using a stronger magnet on what happens to the needle of the galvanometer. A step-up transformer is used to step up the output voltage of a power station from 25 000 V to 400 000 V for transmission along power lines. The number of turns on the secondary coil is 36 000. Calculate the number of turns on the primary coil. number of turns =
0625_s22_qp_43
THEORY
2022
Paper 4, Variant 3
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