In going from a rarer to a denser medium, light loses some speed. What happens to energy carried by light waves ?

Options

A. decreases
B. increases
C. remains the same
D. none of the above

Answer

To solve the question regarding what happens to the energy carried by light waves when they transition from a rarer to a denser medium, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Medium Transition**:
- When light travels from a rarer medium (like air) to a denser medium (like glass or water), its speed decreases. This is a fundamental property of light as it interacts with different materials.

2. **Using the Wave Equation**:
- The relationship between the speed of light (c), frequency (ν), and wavelength (λ) is given by the equation:
\[ c = ν \cdot λ \]
- Here, c is the speed of light in the medium, ν is the frequency, and λ is the wavelength.

3. **Effect on Wavelength**:
- As light enters a denser medium, its speed decreases. Since the frequency (ν) of light is determined by the source and remains constant during the transition, the decrease in speed must result in a decrease in wavelength (λ).
- Therefore, we can conclude:
\[ λ \text{ decreases as } c \text{ decreases.} \]

4. **Energy of Light Waves**:
- The energy (E) of a photon is given by the equation:
\[ E = h \cdot ν \]
- In this equation, h is Planck's constant and ν is the frequency.

5. **Conclusion on Energy**:
- Since the frequency (ν) does not change when light moves from a rarer to a denser medium, the energy (E) of the light waves remains constant.
- Thus, the energy carried by light waves does not change despite the change in speed and wavelength.

### Final Answer:
The energy carried by light waves remains the same when transitioning from a rarer to a denser medium because the frequency of the light does not change.

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