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Single source of disturbance - wave fronts

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Single source of disturbance - wave fronts

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Ripple Tank Single Point Source with Cork

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What do you observe?

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Moving source of waves squash waves in front of it and stretches waves behind it

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Moving source of waves squash waves in front of it and stretches waves behind it

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Discovered the Doppler effect in 1842.

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When the source of a sound is moving towards you, the pitch sounds higher than that of the source.

When the source moves away from you the pitch sounds lower.

This is known as the DOPPLER EFFECT.

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The Big Bang Theory - Doppler Effect (Compilation)

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Doppler Effect  Explained in simple terms

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Doppler effect explained with the mathematics

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Examples
(use 340 m.s⁻¹ for speed of sound and 3 x 10⁸ m.s⁻¹ for speed of light)

1.      An ambulance drives towards a stationary man at a constant speed of 40 m.s⁻¹ with its siren emitting a sound with an average frequency of 320 Hz.

a) What average frequency does the man hear?

b) By how much does the average frequency he hears drop as the ambulance passes him?

c)    If, once passed, the ambulance accelerates will the pitch of sound the man hears INCREASE, DECREASE or STAY THE SAME?

2.
Bobby is driving down a straight road at 35 m.s⁻¹ and hears a siren with a frequency of 400 Hz. He sees a police car behind him. If the actual frequency of the police car siren is 407, what was the speed of the police car?

3.      A boy sprints towards his sister at 12 m.s⁻¹ shouting with sound of frequency 280 Hz. If she is running towards her brother at 8 m.s⁻¹, what is the frequency of the sound she hears?

4.      Most galaxies are moving away from ours. The fastest recorded is moving away from us at 1,89 x 10⁷ m.s⁻¹. If an object there produced light at a frequency of 5,2 x 10¹⁴ Hz, what would be the frequency of that photon when recorded on the earth?

5.      A speed gun uses microwaves with a frequency of 37,4 GHz. If the microwaves bounce off a car moving towards the gun at 160 km.h⁻¹, what will be the frequency of the reflected microwaves?