Doppler Effect: Apparent change in frequency or pitch of a sound detected by a listener when the source and listener have different velocities relative to the medium of sound propagation.
Sound as a Wave
Sound is formed by vibrations in the voice box and can be quantified by amplitude.
Sound is a wave characterized by amplitude (loudness) and frequency (pitch).
Amplitude: Height of wave; related to volume.
Frequency: Number of wave peaks within a specific period; related to pitch.
Wavelength and Frequency Relationship
Longer wavelength = Lower frequency
Shorter wavelength = Higher frequency
Formula: (v = f \times \lambda)
v: Speed of sound
f: Frequency (in Hertz)
(\lambda): Wavelength (in meters)
Application of the Doppler Effect
Scenarios
Stationary Source and Moving Listener
Source is stationary; listener moves.
Moving Source and Stationary Listener
Source moves; listener is stationary.
Mathematical Application
Formula for Doppler Effect:
( f_l = (v \pm v_l) / (v \pm v_s) \times f_s )
f_l: Frequency observed by the listener
v: Speed of sound
v_l: Speed of listener
v_s: Speed of source
f_s: Frequency of source
Using the Formula
Proper Fraction: When (f_l < f_s) (source moving away)
Improper Fraction: When (f_l > f_s) (source moving towards)
Practical Example
Changes in perceived sound frequency when an ambulance approaches and moves away from a listener.
Experiments and Observations
Past Exam Questions
Examples covered various scenarios with a focus on practical application of the Doppler Effect formula.
Conversion of units, understanding wave properties, and effect on frequency and wavelength.
Advanced Concepts
Spectral Lines and Universe Expansion
Study of spectral lines can show movement of stars (Blue Shift vs Red Shift).
Blue Shift: Star moving towards Earth
Red Shift: Star moving away (universe expansion)
Conclusion
Emphasized practical understanding and application of the Doppler Effect.
Encouraged further study through available resources and past examination questions.
Contact and Further Resources
Contact for questions: lung ac dot m.tenkosi at gmail.com
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