Question

Assertion :When source moves towards a stationary observer, the apparent frequency increases. Reason: When source moves towards a stationary observer, the same number of waves are contracted between smaller distance, so effective wavelength decreases and frequency increases.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

From doppler effect

${\eta }^1=\eta \left(\frac{V\pm V_0}{V\pm V_5}\right)$

According to question, ${\eta }^1=\eta \left[\frac{V+O}{V-V_5}\right]$. So aparant frequency has increased. It also due to contraction of wave in shorter distance which results in decrease of effective wave length hence frequency increases.