Concept:According to the Doppler Effect, when a source moves towards a stationary observer, the sound waves get "compressed" in front of the source, leading to a shorter apparent wavelength and a higher apparent frequency.
Formula:$$ f' = \left( \frac{v}{v - v_{\text{source}}} \right) f $$
Solution:- To mathematically yield a higher frequency (\( f_o > f \)), the fraction must be greater than 1.
- This requires the denominator to be smaller than the numerator.
- Using \( (v - u) \) in the denominator correctly models this increase, where \( u \) represents the source velocity.
Why other options are incorrect:Option A describes an observer moving towards a source. Option B describes a source moving away (lower frequency). Option D describes an observer moving away.
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