When wavefronts pass form denser medium to rarer medium the width of the wavefront

Options

A. increases
B. may increases or decreases
C. decreases
D. remains unchanged

Answer

### Step-by-Step Solution:

1. **Understanding the Mediums**:
- We have two mediums: Medium A (denser) and Medium B (rarer).
- The refractive index of Medium A (n1) is greater than that of Medium B (n2), i.e., n1 > n2.

2. **Wavefronts and Rays**:
- When light travels from a denser medium (A) to a rarer medium (B), we can visualize the wavefronts as the surfaces of constant phase of the light waves.
- As the wavefronts reach the interface between the two mediums, they will change direction due to refraction.

3. **Speed of Light in Different Mediums**:
- The speed of light in Medium A (denser) is given by \( V_a = \frac{C}{n1} \).
- The speed of light in Medium B (rarer) is given by \( V_b = \frac{C}{n2} \).
- Since n2 < n1, it follows that \( V_b > V_a \). This means light travels faster in the rarer medium.

4. **Distance Travelled by Light**:
- If we consider a time interval \( T \), the distance travelled by light in Medium A is \( D1 = V_a \cdot T \) and in Medium B is \( D2 = V_b \cdot T \).
- Since \( V_b > V_a \), it follows that \( D2 > D1 \).

5. **Effect on Wavefront Width**:
- As the wavefronts move from the denser medium to the rarer medium, the distance between successive wavefronts increases.
- Therefore, the width of the wavefronts increases when transitioning from a denser medium to a rarer medium.

6. **Conclusion**:
- The correct answer to the question is that the width of the wavefront increases when wavefronts pass from a denser medium to a rarer medium.