1. Do Now: Write down some uses or practical applications of the Doppler Effect Please have your H/W out ready for me to collect with your name on it Rātapu, 16 Here-turi-kōkā 2015

2. Uses of the Doppler Effect  Radar Speed Detectors – by measuring the frequency change in the radar signal, the cops can tell how fast you’re going and ticket you accordingly…

3. Uses of the Doppler Effect  Redshift – Astronomers can tell how fast distant stars and galaxies are moving (and therefore how far away they are) by looking at the frequency change of the light coming from them.

4. Sonic Booms  If the source is going as fast as the wave is travelling, the wavefronts “pile up” to form a shock wave  What does “pile up” mean?  Emitted waves are in-phase and constructively interfere

5. Today’s Learning: LO4: Calculate the value of the Doppler frequency shift

6. Wave speed: v w vwvw vsvs Source speed: v s  If the source is moving away, the observer hears a lower pitch (frequency): Wave frequency: Observed frequency:

7. Wave speed: v w vwvw vsvs Source speed: v s  If the source is approaching, the observer hears a higher pitch (frequency): Wave frequency: Observed frequency:

8. In the exam you will be given:  Source moving away: use the + sign (gives a lower pitch / frequency)  Source approaching: use the – sign (gives a higher pitch / frequency) So you will need to remember:

9. An ambulance travelling at a speed of 30.0 ms -1 sounds a siren of frequency 400 Hz. The speed of sound is 330 ms -1. What frequency will an observer hear: Example: a)As the ambulance approaches? b)As the ambulance moves away?

10. Tasks: 1) Worksheet 2)Red book: Activity 6A, p77-79 Next lesson: 1) Deriving the Doppler equation 2)Expansion of the universe