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Key Areas covered The Doppler effect is observed in sound and light

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Presentation on theme: "Key Areas covered The Doppler effect is observed in sound and light"— Presentation transcript:

1 Key Areas covered The Doppler effect is observed in sound and light
The Doppler effect causes shifts in wavelengths of sound and light

2 What we will do today State what is meant by the Doppler effect
Describe how the Doppler effect affects sound and carry out an experimental demonstration to show this Carry out calculations on the above

3 The Doppler Effect T. Ferns – 28/9/04 LO’s , ,

4 Doppler Effect: Big Bang Theory Style

5 What is the Doppler effect?
The Doppler effect is the change in frequency you notice when a source of sound waves is moving relative to you. When the source moves towards you, more waves reach you per second and the frequency is increased. If the source moves away from you, fewer waves reach you per second and the frequency is decreased. Doppler Shift Demonstrator

6 Moving source As you can see from the simulation as you move closer to a source, the frequency you, the observer, receives increases. As you move away from a source, the frequency you receive decreases.

7 Calculating the frequency
When a source produces a sound of frequency fs, we can calculate the observed frequency, fo, using a formula. The formula changes slightly depending on whether you move towards the source or move away from the source.

8 Calculating the frequency Moving towards the source
The observed frequency, fo, is higher: fo = fs v . (v - vs) fs = frequency of source v = speed of sound (approx 340ms-1) vs = speed of source Towards = Take away

9 Calculating the frequency Moving away from the source
The observed frequency, fo, is lower: fo = fs v . (v + vs) Away = Add

10 Example 1 fo = fs v . (v - vs) = 800 340 . (340-15) = 800 x 1.04
What is the frequency heard by a person driving at 15 ms-1 toward a blowing factory whistle (f = 800 hz) if the speed of sound in air is 340 ms-1? fo = fs v . (v - vs) = (340-15) = 800 x 1.04 fo = 837 Hz

11 Example 2 fo = fs v . (v + vs) = 800 340 . (340+15) = 800 x 0.931
What frequency would he hear after passing the factory if he continues at the same speed? fo = fs v . (v + vs) = (340+15) = 800 x 0.931 fo = 766 Hz

12 2013 Revised Higher C

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