A cylinderical tube, open at one end and closed at the other, is in acoustic unison (resonance) with an external source of sound of singal frequency held at the open end of the tube, in its fundamental note.
Then :

A. the displacement wave from the source gets reflected with a phase change of `pi` at the closed end
B. the pressrue wave from the source get reflected without a phase change at the closed end
C. the wave reflected from the closed and again gets reflected at the open end
D. the wave reflected from the closed end does not suffer reflection at the open end

Options

A. the displacement wave from the source gets reflected with a phase change of `pi` at the closed end
B. the pressrue wave from the source get reflected without a phase change at the closed end
C. the wave reflected from the closed and again gets reflected at the open end
D. the wave reflected from the closed end does not suffer reflection at the open end

Explanation

To solve the problem, we need to analyze the behavior of sound waves in a cylindrical tube that is open at one end and closed at the other. The tube is in resonance with an external sound source at its fundamental frequency. Let's break down the options step by step.

### Step 1: Understanding Wave Reflection at the Closed End
When a sound wave travels down the tube and reaches the closed end, it reflects back. For a displacement wave, the reflection at a closed boundary (closed end) involves a phase change of π (180 degrees). This means that the wave inverts upon reflection.

**Hint:** Remember that a closed end reflects waves with a phase change, while an open end reflects without a phase change.

### Step 2: Understanding Wave Reflection at the Open End
At the open end of the tube, the behavior is different. Here, the displacement wave reflects without any phase change. This is because the open end allows the wave to maintain its original phase.

**Hint:** Think about how an open end allows the wave to "escape" without inversion.

### Step 3: Analyzing Pressure Waves
For pressure waves, the situation is slightly different. Pressure waves do not undergo any phase change at either the closed or open end. This means that when a pressure wave reflects at the closed end, it does so without any phase change.

**Hint:** Consider how pressure waves behave differently from displacement waves at boundaries.

### Step 4: Evaluating Each Option
Now let's evaluate each of the options given in the question:

- **Option A:** The displacement wave from the source gets reflected with a phase change of π at the closed end.
**True** - As discussed, this is correct.

- **Option B:** The pressure wave from the source gets reflected without a phase change at the closed end.
**True** - Pressure waves do not undergo phase change at the closed end.

- **Option C:** The wave reflected from the closed end again gets reflected at the open end.
**True** - The wave reflects at both ends, with the appropriate phase changes.

- **Option D:** The wave reflected from the closed end does not suffer reflection at the open end.
**False** - There is reflection at both ends; this statement is incorrect.

### Conclusion
The correct options are A, B, and C. Option D is incorrect.