When a fire brigade approaches to a stationary listener, the frequency of sound of its siren received by the listener
Correct answer: D. Becomes greater than the frequency of the original sound.
- A. Varies unpredictably.
- B. Remains the same as the original sound.
- C. Becomes less than the frequency of the original sound.
- D. Becomes greater than the frequency of the original sound.
Explanation
When a fire brigade approaches a stationary listener, the sound waves from the siren are compressed, causing the listener to perceive a higher frequency than the original sound. This phenomenon is explained by the Doppler effect, which describes how the frequency of a wave changes for an observer moving relative to the wave source. Therefore, the correct answer is that the frequency of the sound becomes greater than the original frequency. The options that suggest the frequency remains the same or becomes less are incorrect because they do not account for the relative motion between the source and the listener.
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About Speed of Sound
The speed of sound depends on the properties of the medium, including its elasticity and density, and in gases it varies mainly with temperature. Questions connect speed with frequency and wavelength, compare sound in solids, liquids and gases, and distinguish the speed of propagation from the oscillating particles' motion.
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