(455) Doppler effect introduction [IB Physics SL/HL]

Introduction to the Doppler Effect

• The Doppler Effect: Change in frequency of sound or light due to movement of the source or observer.

Key Concepts

• Movement: Affects perceived frequency; can be a moving source or moving observer.

• Frequency Change: When an object moves toward an observer, frequency increases (higher pitch for sound); moving away results in lower frequency.

Equation

• V = F λ:

  • Where V = speed of wave, F = frequency, λ = wavelength.

  • If V is constant, F and λ are inversely proportional.

Examples

• Moving Source:

  • As a moving source like a car emits sound, waves compress in the direction of movement (higher frequency) and stretch out behind it (lower frequency).

• Observer Position:

As an observer moves toward the source, they encounter higher frequency waves (compressed) and lower frequency waves as they move away (stretched).

Sound vs Light

• Sound:

  • Higher frequency when approaching (higher pitch) and lower frequency when receding (lower pitch).

    • Example: Formula 1 car: sound pitch increases as it approaches; decreases as it moves away.

• Light:

  • Moving toward = lower wavelength (blue-shifted), moving away = higher wavelength (red-shifted).

    • Example: Stars moving toward Earth appear bluer; moving away appears redder.

Conclusion

• Observational Effects:

  • Sound frequency change noted through pitch; light wavelength shift characterized as blue or red shift based on movement relative to the observer.