Question

When a source of sound moves towards a stationary observer, the observed frequency is:

• A. more than actual frequency
• B. less than actual frequency
• C. same as actual frequency
• D. zero

Hint:

Approaching $\rightarrow$ Frequency increases; Receding $\rightarrow$ Frequency decreases.

Answer 1

The Correct Option is A

Step 1: Concept
The Doppler Effect describes the change in frequency due to relative motion.
Step 2: Analysis
Apparent frequency $n' = n \left(\frac{v}{v - v_{s}}\right)$. Since the denominator $(v - v_{s})$ is smaller than $v$, $n'>n$.
Step 3: Conclusion
The frequency heard by the observer is higher than the source frequency.
Final Answer: (A)