When light enters from air to water, then its

Options

A. frequency increases and speed decreases
B. frequency is same but the wavelength is smaller in water than in air
C. frequency is same but the wavelength in water is greater than in air
D. frequency decreases and wavelength is smaller in water than in air

Explanation

To solve the question "When light enters from air to water, then its...", we will analyze the behavior of light as it transitions between two different media: air and water.

### Step-by-Step Solution:

1. **Identify the Media and Their Refractive Indices**:
- The refractive index of air (μ_air) is approximately 1.
- The refractive index of water (μ_water) is approximately 4/3.

2. **Determine the Nature of the Transition**:
- Light is moving from a rarer medium (air) to a denser medium (water).
- In general, when light travels from a rarer medium to a denser medium, it bends towards the normal.

3. **Understand the Relationship Between Speed, Frequency, and Wavelength**:
- The speed of light in a medium is given by the formula:
\[ V = \frac{c}{\mu} \]
where \( c \) is the speed of light in vacuum (approximately \( 3 \times 10^8 \) m/s) and \( \mu \) is the refractive index of the medium.
- Since the refractive index of water is greater than that of air, the speed of light in water (V_water) will be less than the speed of light in air (V_air).

4. **Frequency of Light**:
- The frequency of light (f) is determined by the source and remains constant when light passes from one medium to another.
- Therefore, the frequency of light does not change when it enters water from air.

5. **Wavelength of Light**:
- The relationship between speed, frequency, and wavelength (λ) is given by:
\[ V = f \cdot \lambda \]
- Since the speed of light decreases when it enters water, and the frequency remains constant, the wavelength must also decrease.
- Thus, the wavelength of light in water (λ_water) is less than the wavelength of light in air (λ_air).

6. **Conclusion**:
- When light enters from air to water, its frequency remains the same, but its wavelength decreases.

### Final Answer:
- The correct statement is: "When light enters from air to water, its frequency remains the same, but its wavelength decreases."