Statement(A): The reflection of sound from an extended object is echo
Statement(B): The super position of waves of same frequency is beats
Statement(C): The apparent change in frequency of source of sound due to relative motion between source and observer is Doppler effect
Statement(D): The super position of wave of slightly differ in frequency is stationary waves

Options

A. A, B, C, D are true
B. only A, D, B are true
C. only A & C are true
D. only B, C are true

Answer

To analyze the statements provided in the question, we will evaluate each statement one by one to determine its validity.

### Step-by-Step Solution:

1. **Evaluate Statement A:**
- **Statement:** The reflection of sound from an extended object is echo.
- **Analysis:** This statement is true. When sound waves hit a surface and reflect back, the phenomenon is known as an echo. An echo occurs when the sound reflects off a large object and returns to the listener after a delay.
- **Conclusion:** Statement A is **True**.

2. **Evaluate Statement B:**
- **Statement:** The superposition of waves of the same frequency is beats.
- **Analysis:** This statement is false. Beats are produced by the interference of two waves that have slightly different frequencies, not the same frequency. When two waves of the same frequency interfere, they produce a wave of the same frequency, but with varying amplitude, not beats.
- **Conclusion:** Statement B is **False**.

3. **Evaluate Statement C:**
- **Statement:** The apparent change in frequency of the source of sound due to relative motion between the source and observer is Doppler effect.
- **Analysis:** This statement is true. The Doppler effect describes the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. It is commonly experienced with sound waves when a source moves towards or away from an observer.
- **Conclusion:** Statement C is **True**.

4. **Evaluate Statement D:**
- **Statement:** The superposition of waves of slightly different frequencies is stationary waves.
- **Analysis:** This statement is false. The superposition of waves of slightly different frequencies results in beats, not stationary waves. Stationary waves are formed when two waves of the same frequency and amplitude travel in opposite directions and interfere with each other.
- **Conclusion:** Statement D is **False**.

### Final Summary:
- **True Statements:** A and C
- **False Statements:** B and D