A ray of white light passes through a rectangular glass slab, entering and emerging at parallel faces. The angle of incidence measured from the normal to the glass surface, is large. Then

Options

A. White light will emerge from the slab
B. The light emerging from the slab will have a number of parallel, colored rays
C. The emergent rays will not form a spectrum on a screen
D. Colors will be seen if the emergent rays enter the eye directly

Answer

To solve the problem of a ray of white light passing through a rectangular glass slab and emerging at parallel faces, we can break down the process into several steps:

### Step-by-Step Solution:

1. **Understanding the Setup**:
- We have a rectangular glass slab with two parallel faces. A ray of white light strikes the first face at a large angle of incidence.

2. **Incident Ray**:
- The ray of white light enters the glass slab at an angle (let's denote it as θ1) which is measured from the normal to the surface of the glass.

3. **Refraction at First Surface**:
- According to Snell's Law, when the light enters the glass slab, it will bend towards the normal because the refractive index of glass is greater than that of air. The relationship can be expressed as:
\[ n_1 \sin(\theta_1) = n_2 \sin(\theta_2) \]
- Here, \( n_1 \) is the refractive index of air (approximately 1), \( n_2 \) is the refractive index of glass (approximately 1.5), and \( \theta_2 \) is the angle of refraction inside the glass.

4. **Traveling Through the Glass Slab**:
- Once the light enters the glass, it travels in a straight line until it reaches the second face of the slab.

5. **Refraction at Second Surface**:
- Upon reaching the second face, the light will again refract. This time, it will bend away from the normal as it exits the glass into the air. The angle of incidence at this face is equal to the angle of refraction from the first face (due to parallel faces).
- Applying Snell's Law again:
\[ n_2 \sin(\theta_2) = n_1 \sin(\theta_3) \]
- Here, \( \theta_3 \) is the angle of emergence, which will be equal to the angle of incidence \( \theta_1 \) due to the symmetry of the setup.

6. **Emerging Ray**:
- The ray of light emerges from the glass slab at an angle \( \theta_3 \), which is equal to \( \theta_1 \). Therefore, the emergent ray is parallel to the incident ray.

7. **Color Dispersion**:
- Since white light consists of multiple wavelengths, each wavelength will refract slightly differently. However, because the faces of the slab are parallel, the different colors will emerge parallel to each other, resulting in a negligible dispersion of colors. Thus, the light emerging from the slab remains white light.

### Final Conclusion:
- The ray of white light emerges from the glass slab parallel to the incident ray, and the spectrum formed is negligible due to the parallel nature of the glass slab's faces.