(A) : When a source moves towards a stationary observer, the speed of source relative to the observer remains unchanged.
(R): The apparent change in frequency is due to change in the wavelength brought by the motion of the source.

Options

A. Both 'A' and 'R' are true and 'R' is the correct, explanation of 'A'.
B. Both 'A' and 'R' are true and 'R' is not the correct explanation of 'A'
C. A' is true and 'R' is false
D. Both 'A' and 'R' are false

Answer

To analyze the statements given in the question regarding the Doppler effect, we need to evaluate both the Assertion (A) and the Reason (R) independently.

### Step 1: Understanding the Assertion (A)
The assertion states: "When a source moves towards a stationary observer, the speed of the source relative to the observer remains unchanged."

- **Analysis**: This statement is incorrect. When a source moves towards a stationary observer, the relative speed between the source and the observer actually changes. The speed of sound remains constant in the medium, but the motion of the source affects how the waves are perceived by the observer.

### Step 2: Understanding the Reason (R)
The reason states: "The apparent change in frequency is due to change in the wavelength brought by the motion of the source."

- **Analysis**: This statement is partially correct. The apparent change in frequency (Doppler effect) is indeed related to the motion of the source and the observer. However, it is not solely due to a change in wavelength; it is also influenced by the relative velocities of the source and the observer. When the source moves towards the observer, the waves are compressed, leading to a higher frequency (and shorter wavelength) perceived by the observer.

### Step 3: Conclusion
- Since the assertion (A) is incorrect and the reason (R) is partially correct but does not fully explain the phenomenon, we conclude that the correct relationship between the two statements is that (A) is false and (R) does not adequately support (A).

### Final Answer
- The Assertion (A) is False.
- The Reason (R) is True but does not correctly justify (A).

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