The Doppler Effect Pg 503

Bell Ringer  What do you observe when an ambulance with a flashing siren comes towards you? Away from you? Why?

Stationary source of sound  Like a stone thrown into a still pond  The stationary source emits sound waves which can be represented by concentric circles

If the sound source starts moving  The sound waves will also move  If the sound source moves to the right, the sound waves also move to the right

Frequency – How often?  For a person at B, frequency _________.  For a person at A, frequency _________.  As a wave source approaches, an observer encounters waves with HIGHER frequency.  As a wave source moves away, the observer encounters waves with LOWER frequency.  This apparent change in frequency due to the motion of the sound source (or observer) is called the DOPPLER EFFECT.

Pitch & Frequency  As frequency increases, pitch ________.  So as a siren comes closer to an observer, its frequency _____ and its pitch ________. The pitch is higher when the source moves towards you and lower when the source moves away from you.

Doppler Effect in Sound  Occurs either when  1) The sound source moves TOWARDS OR AWAY from the observer.  2) The observer moves TOWARDS OR AWAY from the sound source.

Frequency, Wavelength & Speed  In the Doppler effect, 1. Frequency changes – either increases or decreases 2. Wavelength changes – if freq increases then wavelength decreases & vice versa 3. But speed always remains the same.

Doppler effect in Light  Just like in Sound, the Doppler effect also occurs in Light.  As a light source approaches, there is an increase in its measured frequency and this is called a BLUE SHIFT.  As a light source goes away, there is an decrease in its measured frequency and this is called a RED SHIFT.

Applications of Doppler Effect  Radar Guns  Doppler measurement  of wind speed

Doppler applets & worksheet Doppler Effect Applets: er.html er.html

Next class  Chapter test  Pg 508  Q 15,16, 38, 45, 46,47,48