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6.1 An ambulance is moving towards a stationary listener at a constant speed of 30 m∙s-1. The siren of the ambulance emits sound waves having a wavelength of 0,28 m. Take the speed of sound in air as 340 m∙s-1.
6.1.1 State the Doppler effect in words. (2)
6.1.2 Calculate the frequency of the sound waves emitted by the siren as heard by the ambulance driver. (3)
6.1.3 Calculate the frequency of the sound waves emitted by the siren as heard by the listener. (5)
6.1.4 How would the answer to QUESTION 6.1.3 change if the speed of the ambulance were LESS THAN 30m∙s-1? Write down only INCREASES, DECREASES or REMAINS THE SAME. (1)
6.2 An observation of the spectrum of a distant star shows that it is moving away from the Earth.
Explain, in terms of the frequencies of the spectral lines, how it is possible to conclude that the star is moving away from the Earth. (2)
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