7.1. Progressive waves
A subsection of Physics, 9702, through 7. Waves
Listing 10 of 202 questions
By reference to the direction of transfer of energy, state what is meant by a longitudinal wave. A vehicle travels at constant speed around a wide circular track. It continuously sounds its horn, which emits a single note of frequency 1.2 kHz. An observer is a large distance away from the track, as shown in the view from above in . vehicle direction of travel track observer (not to scale) shows the variation with time of the frequency f of the sound of the horn that is detected by the observer. The time taken for the vehicle to travel once around the track is T. 0.8 1.0 1.2 1.4 1.6 f / kHz time 3T T 2T Explain why the frequency of the sound detected by the observer is sometimes above and sometimes below 1.2 kHz. State the name of the phenomenon in . On , mark with a letter X the position of the vehicle when it emitted the sound that is detected at time T. On , mark with a letter Y the position of the vehicle when it emitted the sound that is detected at time 9T 4 . The speed of the sound in the air is 320 m s–1. Use to determine the speed of the vehicle in . speed = m s–1
9702_w21_qp_21
THEORY
2021
Paper 2, Variant 1
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A child sits on the ground next to a remote-controlled toy car. At time t = 0, the car begins to move in a straight line directly away from the child. The variation with time t of the velocity of the car along this line is shown in . t / s velocity / m s–1 The car’s horn continually emits sound of frequency 925 Hz between time t = 0 and time t = 6.0 s. The speed of the sound in the air is 338 m s–1. Describe qualitatively the variation, if any, in the frequency of the sound heard, by the child, that was emitted from the car horn: from time t = 0 to time t = 2.0 s from time t = 4.0 s to time t = 6.0 s. Determine the frequency, to three significant figures, of the sound heard, by the child, that was emitted from the car horn at time t = 3.0 s. frequency = Hz Determine the time taken for the sound emitted at time t = 4.0 s to travel to the child. time taken = s
9702_w21_qp_22
THEORY
2021
Paper 2, Variant 2
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When audio signals are transmitted over long distances, modulation of radio waves is used. Suggest a reason why modulation is used. State a technical advantage and a technical disadvantage of using frequency modulation rather than amplitude modulation. advantage: disadvantage: An audio signal of amplitude 2.0 μV and frequency 4.2 kHz is to be transmitted using a carrier wave of amplitude 10.0 mV and frequency 100 kHz. Either amplitude modulation or frequency modulation may be used. The amplitude modulation is at a rate of 1 mV μV–1. The frequency modulation is at a rate of 5 kHz μV–1. Complete Table 5.1 to show the maximum and minimum values of the amplitude and of the frequency of the modulated wave for each type of modulation. Table 5.1 amplitude / mV frequency / kHz minimum maximum minimum maximum amplitude modulation frequency modulation For the amplitude modulated wave in , determine the bandwidth. bandwidth = kHz
9702_w21_qp_42
THEORY
2021
Paper 4, Variant 2
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Two progressive sound waves meet to form a stationary wave. The two waves have the same amplitude, wavelength, frequency and speed. State the other condition that must be fulfilled by the two waves in order for them to produce the stationary wave. A stationary wave is formed on a string that is stretched between two fixed points A and B. shows the string at time t = 0 when each point is at its maximum displacement. A B Distance AB is 0.80 m. The period of the stationary wave is 0.016 s. On , sketch a solid line to show the position of the string: ● at time t = 0.004 s (label this line P) ● at time t = 0.024 s (label this line Q). Determine the speed of a progressive wave along the string. speed = m s–1 A beam of vertically polarised light of intensity I0 is incident normally on a polarising filter that has its transmission axis at 30° to the vertical, as shown in . 30° intensity I0 intensity I1 intensity I2 vertically polarised incident light beam, transmitted beam, transmitted beam, polarising filter with transmission axis at 30° to the vertical second polarising filter with transmission axis at 90° to the vertical The transmitted light from the first polarising filter has intensity I1. This light is then incident normally on a second polarising filter that has its transmission axis at 90° to the vertical. The transmitted light from the second filter has intensity I2. Calculate: the ratio I1 I0 I1 I0 = the ratio I2 I0 . I2 I0 =
9702_w22_qp_22
THEORY
2022
Paper 2, Variant 2
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Questions Discovered
202