When a ray goes from an optically rarer medium to a denser medium, it:

Options

A. goes straight
B. bends away from normal
C. bends towards normal
D. reflect back

Explanation

To solve the question "When a ray goes from an optically rarer medium to a denser medium, it:", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Mediums**:
- An optically rarer medium has a lower refractive index compared to a denser medium. For example, air is rarer than water.

2. **Identifying the Behavior of Light**:
- When light travels from a rarer medium to a denser medium, it undergoes refraction. Refraction is the bending of light as it passes from one medium to another.

3. **Applying Snell's Law**:
- Snell's Law states that \( n_1 \sin(i) = n_2 \sin(r) \), where:
- \( n_1 \) is the refractive index of the rarer medium,
- \( n_2 \) is the refractive index of the denser medium,
- \( i \) is the angle of incidence,
- \( r \) is the angle of refraction.

4. **Comparing Refractive Indices**:
- In this case, \( n_1 < n_2 \). Therefore, as light enters the denser medium, the refractive index increases.

5. **Analyzing the Angles**:
- Since \( n_2 > n_1 \), for the equation \( n_1 \sin(i) = n_2 \sin(r) \) to hold, the angle of refraction \( r \) must be less than the angle of incidence \( i \). This means that the light ray bends towards the normal.

6. **Conclusion**:
- Thus, when a ray goes from an optically rarer medium to a denser medium, it bends towards the normal.

### Final Answer:
When a ray goes from an optically rarer medium to a denser medium, it bends towards normal.

---