Stethoscope used by doctors is based on which phenomenon ?

Explanation

### Step-by-Step Solution:

1. **Understanding the Stethoscope**: A stethoscope is a medical instrument used by doctors to listen to the internal sounds of a patient's body, particularly the heart and lungs.

2. **Identifying the Phenomenon**: The stethoscope operates based on the phenomenon of sound waves. Specifically, it utilizes the **reflection of sound waves**.

3. **Mechanism of Action**:
- The doctor places the chest piece of the stethoscope on the patient's chest. This chest piece has a sensitive membrane that detects sounds produced by the body, such as the heartbeat or blood flow.
...