9702 · 7.3
Doppler effect for sound waves
Prepare to master the **Doppler effect**, a fascinating phenomenon where the **frequency** of a wave appears to change due to **relative motion** between its source and an observer. This concept is vital for Cambridge Physics (9702) and explains everyday experiences like the changing pitch of an ambulance siren as it passes. This pilot aligns with **Senpai Corner** AS notes (2025–2027) for topic **7.3**.
Need to know
What you need to know
- $f_o$: The observed frequency detected by the listener.
- $f_s$: The actual frequency emitted by the sound source.
- $v$: The speed of sound in the surrounding medium (e.g., air).
- $v_s$: The speed of the sound source relative to the medium.
- Use the **minus sign ($-v_s$)** in the denominator when the source is moving *towards* the observer (results in a higher $f_o$).
- Use the **plus sign ($+v_s$)** in the denominator when the source is moving *away* from the observer (results in a lower $f_o$).
Explanation
Doppler effect for sound waves
- $f_o$: The observed frequency detected by the listener.
- $f_s$: The actual frequency emitted by the sound source.
- $v$: The speed of sound in the surrounding medium (e.g., air).
- $v_s$: The speed of the sound source relative to the medium.