An observer approaches towards a stationary source of sound at constant velocity and recedes away at the same speed. The graph of wavelength observed with time is:

Options

A.
B.
C.
D.

Explanation

To solve the problem, we need to analyze the situation where an observer approaches and then recedes from a stationary sound source. We will derive the relationship between the observed wavelength and time for both cases.

### Step 1: Understand the scenario
- An observer is moving towards a stationary sound source with a constant velocity \( v_0 \).
- After reaching a certain point, the observer then moves away from the source at the same speed \( v_0 \).

### Step 2: Determine the frequency when approaching the source
When the observer approaches the source, the apparent frequency \( f' \) can be calculated using the formula:
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