21. Alternating currents
A section of Physics, 9702
Listing 10 of 55 questions
A bridge rectifier using four ideal diodes is shown in . R A B The sinusoidal alternating electromotive force (e.m.f.) applied between points A and B has a root- mean-square (r.m.s.) value of 7.0 V. On , circle the diodes that conduct when point B is positive with respect to point A. Calculate the maximum potential difference VMAX across resistor R. VMAX = V A capacitor is connected into the circuit to produce smoothing of the potential difference across resistor R. The variation with time t of the potential difference V across resistor R is shown in . t V magnitude of ripple On , draw the symbol for a capacitor, connected so as to produce smoothing. State the effect, if any, on the magnitude of the ripple on V when, separately: 1. a capacitor of larger capacitance is used 2. the resistor R has a smaller resistance.
9702_w19_qp_41
THEORY
2019
Paper 4, Variant 1
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A bridge rectifier using four ideal diodes is shown in . R A B The sinusoidal alternating electromotive force (e.m.f.) applied between points A and B has a root- mean-square (r.m.s.) value of 7.0 V. On , circle the diodes that conduct when point B is positive with respect to point A. Calculate the maximum potential difference VMAX across resistor R. VMAX = V A capacitor is connected into the circuit to produce smoothing of the potential difference across resistor R. The variation with time t of the potential difference V across resistor R is shown in . t V magnitude of ripple On , draw the symbol for a capacitor, connected so as to produce smoothing. State the effect, if any, on the magnitude of the ripple on V when, separately: 1. a capacitor of larger capacitance is used 2. the resistor R has a smaller resistance.
9702_w19_qp_43
THEORY
2019
Paper 4, Variant 3
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Use An ideal transformer has 5000 turns on its primary coil. It is to be used to convert a mains supply of 230 V r.m.s. to an alternating voltage having a peak value of 9.0 V. Calculate the number of turns on the secondary coil. number = ……………………………… The output from the transformer is to be full-wave rectified. shows part of the rectifier circuit. A B R On , draw diode symbols to complete the diagram of the rectifier such that terminal A of the resistor R is positive with respect to terminal B, the symbol for a capacitor connected to provide smoothing of the potential difference across the resistor R. Examiner’s Use shows the variation with time t of the smoothed potential difference V across the resistor R. V t1 t3 t4 t t2 State the interval of time during which the capacitor is being charged from the transformer. from time ………… to time …………… The resistance of the resistor R is doubled. On , sketch the variation with time t of the potential difference V across the resistor.
9702_s07_qp_4
THEORY
2007
Paper 4, Variant 0
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A sinusoidal alternating voltage is to be rectified. Suggest one advantage of full-wave rectification as compared with half-wave rectification. The rectification is produced using the circuit of . A B R All the diodes may be considered to be ideal. The variation with time t of the alternating voltage applied to the circuit is shown in and in . voltage t voltage t On the axes of , draw a graph to show the variation with time t of the potential difference across diode A. On the axes of , draw a graph to show the variation with time t of the potential difference across diode B. On , draw the symbol for a capacitor, connected into the circuit so as to provide smoothing. shows the variation with time t of the smoothed potential difference across the resistor R in . potential difference t 1. State how the amount of smoothing may be increased. 2. On , draw the variation with time t of the potential difference across resistor R for increased smoothing.
9702_w09_qp_41
THEORY
2009
Paper 4, Variant 1
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The circuit for a full-wave rectifier using four ideal diodes is shown in . Y B A R X input A resistor R is connected across the output AB of the rectifier. On , draw a circle around any diodes that conduct when the terminal X of the input is positive with respect to terminal Y, label the positive (+) and the negative (–) terminals of the output AB. The variation with time t of the potential difference V across the input XY is given by the expression V = 5.6 sin 380t where V is measured in volts and t is measured in seconds. The variation with time t of the rectified potential difference across the resistor R is shown in . rectified potential difference / V t2 t t1 Use the expression for the input potential difference V, or otherwise, to determine the root-mean-square (r.m.s.) potential difference Vr.m.s. of the input, Vr.m.s. = V the number of times per second that the rectified potential difference at the output reaches a peak value. number = A capacitor is now connected between the terminals AB of the output. The capacitor reduces the variation (the ripple) in the output to 1.6 V. On , sketch the variation with time t of the smoothed output voltage for time t = t1 to time t = t2. Suggest and explain the effect, if any, on the mean power dissipation in resistor R when the capacitor is connected between terminals AB.
9702_w17_qp_42
THEORY
2017
Paper 4, Variant 2
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State what is meant by rectification of an alternating voltage. State the difference between half-wave rectification and full-wave rectification. Complete to show a circuit that produces half-wave rectification of an alternating input voltage VIN to produce output voltage VOUT across the resistor R. VIN VOUT R C State the purpose of the capacitor C in the circuit of . The input voltage VIN in is a square wave. shows the variation of VIN with time t. –12 VIN / V +12 0.01 0.02 t / s 0.03 0.04 shows the variation of VOUT with t. VOUT / V 0.01 0.02 t / s 0.03 0.04 The maximum energy stored in the capacitor is 0.041 J. Show that the capacitance of C is 570 μF. Determine the resistance of R. resistance = Ω
9702_w24_qp_41
THEORY
2024
Paper 4, Variant 1
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State what is meant by rectification of an alternating voltage. State the difference between half-wave rectification and full-wave rectification. Complete to show a circuit that produces half-wave rectification of an alternating input voltage VIN to produce output voltage VOUT across the resistor R. VIN VOUT R C State the purpose of the capacitor C in the circuit of . The input voltage VIN in is a square wave. shows the variation of VIN with time t. –12 VIN / V +12 0.01 0.02 t / s 0.03 0.04 shows the variation of VOUT with t. VOUT / V 0.01 0.02 t / s 0.03 0.04 The maximum energy stored in the capacitor is 0.041 J. Show that the capacitance of C is 570 μF. Determine the resistance of R. resistance = Ω
9702_w24_qp_43
THEORY
2024
Paper 4, Variant 3
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A bridge rectifier contains four ideal diodes A, B, C and D, as shown in . input $ % & / N ' The output of the rectifier is connected to a load L of resistance 2.4 kΩ. On , mark with the letter P the positive terminal of the load. The variation with time t of the potential difference V across the input to the rectifier is shown in Fig. 11. 2. –8 –6 –4 –2 9 / V W LQSXW Calculate the root-mean-square (r.m.s.) current in the load L. r.m.s. current = A The potential difference across the load L is to be smoothed using a capacitor. On , draw the symbol for a capacitor, connected to produce smoothing. The minimum potential difference across the load L with the smoothing capacitor connected is 3.0 V. On , sketch the variation with time t of the potential difference across the load L.
9702_s16_qp_42
THEORY
2016
Paper 4, Variant 2
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12 Data may be transmitted as an analogue signal or as a digital signal. Explain what is meant by 1. an analogue signal, 2. a digital signal. State two advantages of the transmission of data in digital form. 1. 2. The block diagram of represents a system for the digital transmission of analogue data. analogue signal ADC multi-channel cable DAC output Describe the function of the ADC (analogue-to-digital converter). Suggest why the transmission cable has a number of channels.
9702_w10_qp_43
THEORY
2010
Paper 4, Variant 3
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The variation with time t of the voltage level of part of an analogue signal is shown in . 0.25 0.50 0.75 1.00 1.25 1.50 time t / ms voltage level The signal is sampled at 0.25 ms intervals. Each sample is converted into a four-bit digital number. lists various times t at which the voltage level is sampled. The digital number for time t = 0 is shown. time t / ms 0.25 0.50 0.75 1.00 1.25 1.50 digital number On , underline the most significant bit (MSB) for the digital number at time t = 0. Complete for the times shown. After transmission of the digital numbers, the signal is passed through a digital-to-analogue converter (DAC). On , plot the transmitted analogue signal from the DAC. 0.25 0.50 0.75 1.00 1.25 1.50 time t / ms voltage level The transmitted signal in has less detail than the original signal in . Suggest and explain two means by which the level of detail in the transmitted signal could be increased. 1. 2.
9702_s16_qp_41
THEORY
2016
Paper 4, Variant 1
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Questions Discovered
55