White light is incident normally on a glass slab. Inside the glass slab,

Options

A. red light travels faster than other colours
B. violet light travels faster than other colours
C. yellow light travels faster than other colours
D. all colours travels with the same speed.

Answer

### Step-by-Step Solution:

1. **Understanding White Light**: White light is composed of seven different colors: red, orange, yellow, green, blue, indigo, and violet. Each of these colors has a different wavelength.

2. **Incident Light on Glass Slab**: When white light is incident normally on a glass slab, it enters the medium (glass) without any angle of incidence.

3. **Speed of Light in Different Mediums**: The speed of light in a medium is determined by the refractive index (μ) of that medium. The refractive index is defined as:
\[ \mu = \frac{c}{v} \]
where \( c \) is the speed of light in vacuum and \( v \) is the speed of light in the medium.

4. **Refractive Index and Wavelength Relationship**: The refractive index of a medium varies with the wavelength of light. The relationship can be expressed as:
\[ \mu = a + \frac{b}{\lambda^2} \]
where \( a \) and \( b \) are constants, and \( \lambda \) is the wavelength of light.

5. **Effect of Wavelength on Speed**: From the refractive index formula, we can infer that as the wavelength increases, the refractive index decreases. This means that light with a longer wavelength will travel faster in the medium.

6. **Identifying the Color with the Longest Wavelength**: Among the colors of white light, red light has the longest wavelength, followed by orange, yellow, green, blue, indigo, and violet.

7. **Conclusion**: Since red light has the longest wavelength, it will travel faster than the other colors when white light is incident normally on a glass slab.

### Final Answer:
Red light travels faster than other colors when white light is incident normally on a glass slab.

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