4.5.2. The a.c. generator
A subsection of Physics, 0625, through 4. Electricity and magnetism
Listing 10 of 41 questions
A student fits an electrical generator to a bicycle. When the front wheel turns, a magnet rotates between two coils of wire. A lamp is connected to the coils of wire. When the magnet is rotating, the lamp is lit. shows the magnet, the coils of wire and the lamp. N S lamp Describe and explain how rotating the magnet causes the lamp to light. State three ways of increasing the brightness of the bicycle lamp. 1. 2. 3. The generator provides an a.c. supply for the lamp. State the meaning of the term a.c. Describe how a.c. differs from d.c.
0625_w18_qp_32
THEORY
2018
Paper 3, Variant 2
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Describe how a direct current (d.c.) differs from an alternating current (a.c.). shows how the voltage output of an a.c. generator varies with time. 2.0 0.4 0.6 0.8 1.0 4.0 voltage / V time / s 6.0 8.0 –8.0 –6.0 –4.0 –2.0 0.2 time / s 1.2 1.2 1.0 0.8 0.4 0.6 0.2 A heater is connected directly to the a.c. generator and the maximum current in the heater is 0.75 A. On , sketch a graph to indicate how the current in the heater varies with time. 0.25 0.4 0.6 0.8 1.0 0.50 current / A time / s 0.75 1.00 –1.00 –0.75 –0.50 –0.25 0.2 time / s 1.2 1.2 1.0 0.8 0.4 0.6 0.2 Calculate the power produced by the heater when the current is 0.75 A. power = shows the coil ABCD of the a.c. generator between two magnetic poles. A D B C rotation direction N S On , draw a straight arrow to indicate the direction in which side AB of the coil is moving. Label this arrow M. Deduce the direction of the current induced in side AB of the coil and explain your reasoning. The rate at which the coil of the a.c. generator rotates increases. State two ways in which the alternating voltage changes. 1. 2.
0625_w18_qp_43
THEORY
2018
Paper 4, Variant 3
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10 A student is using a cathode-ray oscilloscope to display the waveform of an alternating current supply. The arrangement is shown in . a.c. supply R Y-input switch S cathode-ray oscilloscope When switch S is closed, the trace seen on the screen is as shown in . To get this trace, the settings of the oscilloscope controls are volts / cm: 5 V / cm time-base: 10 ms / cm 1 cm On , carefully draw what is seen on the screen when the frequency of the supply is increased to 1.5 times its previous value. What change, if any, must be made to the oscilloscope volts / cm and time-base controls in order to reduce the peak-to-peak height of the trace to half that shown in ? volts / cm setting time-base setting
0625_s10_qp_32
THEORY
2010
Paper 3, Variant 2
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10 A student is using a cathode-ray oscilloscope to display the waveform of an alternating current supply. The arrangement is shown in . a.c. supply R Y-input switch S cathode-ray oscilloscope When switch S is closed, the trace seen on the screen is as shown in . To get this trace, the settings of the oscilloscope controls are volts / cm: 5 V / cm time-base: 10 ms / cm 1 cm On , carefully draw what is seen on the screen when the frequency of the supply is increased to 1.5 times its previous value. What change, if any, must be made to the oscilloscope volts / cm and time-base controls in order to reduce the peak-to-peak height of the trace to half that shown in ? volts / cm setting time-base setting
0625_s10_qp_33
THEORY
2010
Paper 3, Variant 3
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10 shows an electron beam travelling, in a vacuum, towards the space between a pair of oppositely-charged parallel plates. + + + + + + + + + + – – – – – – – – – – electron beam On , draw carefully the path of the beam between the plates and in the space to the right of the plates. The screen of a cathode-ray oscilloscope (c.r.o.) has a grid of 1 cm squares. shows the trace of an alternating voltage on this screen. 1 cm 1 cm A potential difference of 5.0 V across the Y-plates of the oscilloscope moves the spot on the screen a vertical distance of 1.0 cm. Use to determine the maximum p.d. across the Y-plates. maximum p.d. = The spot on the screen takes 1.0 ms to move 1.0 cm horizontally. From , determine the time for 1 cycle of the waveform on the screen, and use this time to find the frequency of the alternating voltage. frequency =
0625_w13_qp_31
THEORY
2013
Paper 3, Variant 1
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Questions Discovered
41