A source of sound of frequency 600Hz is placed inside of water. The speed of sound is water is `1500m//s` and air it is `300m//s`. The frequency of sound recorded by an observer who is standing in air is

Options

A. 200Hz
B. 3000Hz
C. 120Hz
D. 600Hz

Answer

To solve the problem, we need to understand how sound behaves when it travels from one medium to another. The key points to consider are:

1. **Frequency of Sound**: The frequency of a sound wave is determined by the source of the sound and does not change when the sound wave moves from one medium to another.

2. **Speed of Sound**: The speed of sound varies in different media. In this case, the speed of sound in water is given as 1500 m/s, and in air, it is 300 m/s.

3. **Wavelength**: While the frequency remains constant, the wavelength of the sound wave will change when it moves from one medium to another. The relationship between speed (v), frequency (f), and wavelength (λ) is given by the equation:
\[ v = f \times \lambda \]

### Step-by-Step Solution:

1. **Identify the Given Values**:
- Frequency of the sound source, \( f = 600 \text{ Hz} \)
- Speed of sound in water, \( v_{water} = 1500 \text{ m/s} \)
- Speed of sound in air, \( v_{air} = 300 \text{ m/s} \)

2. **Understand the Frequency Behavior**:
- The frequency of sound does not change when it moves from water to air. Therefore, the frequency recorded by the observer in air will still be the same as that emitted by the source in water.

3. **Conclusion**:
- The frequency of sound recorded by the observer in air is:
\[ f_{air} = f_{water} = 600 \text{ Hz} \]

### Final Answer:
The frequency of sound recorded by an observer who is standing in air is **600 Hz**.