7. Waves
A section of Physics, 9702
Listing 10 of 368 questions
A sinusoidal carrier wave has a constant amplitude and a frequency of 1.2 MHz. The carrier wave is modulated by a signal wave such that a 1.0 V displacement of the signal wave causes a change in frequency of 25 kHz. The signal wave has frequency 8.0 kHz and amplitude 2.0 V. State the name of this type of modulation of the carrier wave. For this modulated carrier wave, determine the variation, if any, in: 1. its amplitude 2. its frequency. An audio signal is transmitted by means of a modulated radio wave. The variation with frequency of the amplitude of the radio wave is shown in . amplitude frequency / kHz For this transmission, determine: the wavelength, in km, of the carrier wave wavelength = km the bandwidth bandwidth = kHz the frequency of the audio signal. frequency = kHz
9702_s21_qp_42
THEORY
2021
Paper 4, Variant 2
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State what is meant by the amplitude modulation (AM) of a radio wave. A radio wave is modulated by an audio signal. The variation with frequency f of the amplitude of the modulated wave is shown in . amplitude f / kHz Determine: the wavelength of the carrier wave wavelength = m the bandwidth of the modulated wave bandwidth = kHz the maximum frequency of the audio signal. maximum frequency = kHz The power of a radio signal at a transmitter is PT. At a receiver, the received power PR is given by the expression PR = 0.082 PT x2 where x is the distance, in metres, between the transmitter and the receiver. For the transmission of this signal, the attenuation is 73 dB. Determine the distance x. x = m
9702_s21_qp_43
THEORY
2021
Paper 4, Variant 3
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For a progressive wave, state what is meant by the frequency. A loudspeaker, microphone and cathode-ray oscilloscope (CRO) are arranged as shown in . microphone loudspeaker CRO The loudspeaker is emitting a sound wave which is detected by the microphone and displayed on the screen of the CRO as shown in . 1.0 cm 1.0 cm The time-base on the CRO is set to 0.50 ms cm−1 and the y-gain is set to 0.20 V cm−1. Calculate: the frequency of the sound wave frequency = Hz the amplitude of the signal received by the CRO. amplitude = V The intensity of the sound wave in is reduced to a quarter of its original intensity without a change in frequency. Assume that the amplitude of the signal received by the CRO is proportional to the amplitude of the sound wave. On , sketch the trace that is now seen on the screen of the CRO. A metal sheet is now placed in front of the loudspeaker in , as shown in . microphone loudspeaker metal sheet CRO A stationary wave is formed between the loudspeaker and the metal sheet. State the principle of superposition. The initial position of the microphone is such that the trace on the CRO has an amplitude minimum. It is now moved a distance of 1.05 m away from the loudspeaker along the line joining the loudspeaker and metal sheet. As the microphone moves, it passes through three positions where the trace has an amplitude maximum before ending at a position where the trace has an amplitude minimum. Determine the wavelength of the sound wave. wavelength = m Use your answers in and to determine the speed of the sound in the air. speed = m s−1
9702_s23_qp_23
THEORY
2023
Paper 2, Variant 3
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Questions Discovered
368