Question

When source of sound moves towards a stationary observer, the apparent frequency heard by him

• A. increases and wavelength also increases.
• B. increases while wavelength decreases.
• C. remains the same while wavelength decreases.
• D. decreases and wavelength remains the same.

Hint:

Source approaching → pitch increases → wavelength decreases.

Answer 1

The Correct Option is B

Concept:
This is the Doppler effect. When the source moves towards the observer:

• Wavefronts get compressed
• Wavelength decreases
• Frequency increases

Step 1: Understand wave behavior. As source approaches, successive waves are emitted from closer positions → spacing between waves reduces.
Step 2: Relation. \[ v = f\lambda \] Since speed of sound \(v\) remains constant:

• \(\lambda\) decreases
• \(f\) increases

Step 3: Conclusion. \[ \text{Frequency increases and wavelength decreases} \]