A sound tone is produced under water. When it enters air

Options

A. its frequency and wavelength increase
B. its frequency and wavelength decrease
C. Wave length decreases and frequency does not change
D. Wave length increases and frequency does not change

Answer

To solve the question about what happens to a sound tone produced underwater when it enters air, we need to analyze the properties of sound waves in different media.

### Step-by-Step Solution:

1. **Understand the Mediums**:
- Sound travels through different mediums, such as water (a liquid) and air (a gas). The speed of sound is different in these mediums.

2. **Speed of Sound**:
- The speed of sound in water is greater than the speed of sound in air. This is an important fact to remember because it affects how sound behaves when transitioning between these two mediums.

3. **Use the Wave Equation**:
- The relationship between speed (V), frequency (F), and wavelength (λ) is given by the equation:
\[ V = F \times \lambda \]
- Here, V is the speed of sound in the medium, F is the frequency, and λ is the wavelength.

4. **Frequency and Medium**:
- The frequency of a sound wave is determined by the source of the sound and does not change when the sound moves from one medium to another. Therefore, when the sound tone produced underwater enters the air, the frequency (F) remains constant.

5. **Wavelength Changes**:
- Since the speed of sound is different in water and air, and the frequency remains constant, the wavelength must change.
- When sound moves from water (higher speed) to air (lower speed), the wavelength decreases because:
\[ \lambda = \frac{V}{F} \]
- Since V (speed of sound) decreases when moving from water to air, and F remains constant, λ must decrease.

6. **Conclusion**:
- Based on the analysis, we conclude that when a sound tone produced underwater enters air, the wavelength decreases while the frequency remains unchanged.

### Final Answer:
The correct option is: **Wavelength decreases and frequency does not change.**