The Doppler EffectThe Doppler Effect

►Time to demonstrateTime to demonstrate►Please cooperatePlease cooperate►See you downstairs, outside by the See you downstairs, outside by the

main entrance in three minutesmain entrance in three minutes

►Any questions???Any questions???►Let’s go!Let’s go!

Let’s think about what your Let’s think about what your heardheard

►Did you hear the Doppler effect?Did you hear the Doppler effect?►Do you understand the Doppler effect?Do you understand the Doppler effect?►Do you know what it means???Do you know what it means???►Let’s ask “Sheldon”…Let’s ask “Sheldon”…►Video pleaseVideo please►Now let’s calculate the Doppler Now let’s calculate the Doppler

effect…effect…

Doppler EffectDoppler Effect

►When the source of sound approaches When the source of sound approaches an observer, the observed frequency of an observer, the observed frequency of the sound increases; when the source the sound increases; when the source moves away from the observer, the moves away from the observer, the observed frequency of the sound observed frequency of the sound decreases.decreases.

►Diagrams of the Doppler Effect ( next Diagrams of the Doppler Effect ( next slide)slide)

Okay, who put this in here!!!Okay, who put this in here!!!

Diagram of the Doppler Diagram of the Doppler EffectEffect

Formula for the Doppler EffectFormula for the Doppler Effect

► ffobsobs= = v vsound sound ffsourcesource

► vvsoundsound ++ v v sourcesource

► Where: fWhere: fobs = obs = frequency observed ( Hz)frequency observed ( Hz)

ffsource source = frequency of source ( Hz)= frequency of source ( Hz)

vvsound sound = velocity of sound ( m/s)= velocity of sound ( m/s)

- if the source is moving toward the observer- if the source is moving toward the observer

+ if the source is moving away from the observer+ if the source is moving away from the observer

Problem #1: Car travellingProblem #1: Car travelling► A car travelling at 100 km/h sounds it horn as it A car travelling at 100 km/h sounds it horn as it

approaches Joseph standing on the highway. approaches Joseph standing on the highway. ► STOP- Okay Joseph, why are you standing on the STOP- Okay Joseph, why are you standing on the

highway????highway????► You are going to get hit!!!You are going to get hit!!!► Get off the highway!Get off the highway!► If the car’s horn has a frequency of 440 Hz and If the car’s horn has a frequency of 440 Hz and

the temperature of the air is 0 the temperature of the air is 0 00C, what is the C, what is the frequency of the sound waves reaching Josephfrequency of the sound waves reaching Joseph

► a) as the car approaches Joseph?a) as the car approaches Joseph?► b) after it has passed Joseph?b) after it has passed Joseph?► Answer:Answer:► a) f a) f obsobs = 480 Hz = 480 Hz► b) f b) f obsobs = 406 Hz = 406 Hz

Your Turn…Your Turn…

►MHR pg. 396 #11-15MHR pg. 396 #11-15

►Doppler Effect: WorksheetDoppler Effect: Worksheet