Read Doppler Effect: Keep Source and Listener Speeds Separate
Sound Doppler shifts depend differently on source and listener motion. Work along the line joining them and keep signs tied to approach or recession.
Doppler Effect with a Moving Listener is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Start with the condition
For an approaching source and listener, use observed frequency = source frequency times (v plus listener-toward-source speed)/(v minus source-toward-listener speed).
Build the governing relation
Compare the two listening situations by subtracting their measured frequencies only after writing both expressions with the same sign convention.
Finish with a physical check
Check the limiting case before selecting an option: remove the special feature in the diagram or make the relevant parameter very large or very small. The result should reduce to a familiar relation.
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- ✓State the physical condition before choosing a formula.
- ✓Keep direction, sign and constraint information explicit.
- ✓Test one limiting case before committing to an option.
Using relative speed in a single denominator incorrectly treats sound as if it travelled instantly between moving bodies.
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