When exposed to sunlight, thin films of oil on water often exhibit brilliant colours due to the phenomenon of

Options

A. interference
B. diffraction
C. dispersion
D. polarisation

Explanation

To solve the question regarding the brilliant colors exhibited by thin films of oil on water when exposed to sunlight, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Scenario**:
- When oil is spilled on water, it forms a thin film on the surface. When sunlight hits this film, we observe different colors.

2. **Identifying the Phenomena**:
- The key phenomena responsible for the observed colors in thin films are **reflection** and **refraction** of light.

3. **Reflection and Refraction**:
- When light from the sun strikes the surface of the oil film, some of it is reflected off the top surface of the oil. This is known as **direct reflection**.
- Simultaneously, some light enters the oil film, travels through it, and reflects off the bottom surface (the oil-water interface). This is known as **internal reflection**.

4. **Interference of Light Waves**:
- The light rays that are reflected from the top surface and the bottom surface travel different distances before reaching the observer's eye.
- Because of this difference in path length, the two rays can interfere with each other. This interference can be **constructive** (where the waves add up) or **destructive** (where the waves cancel each other out).

5. **Resulting Colors**:
- The varying thickness of the oil film causes different wavelengths (colors) of light to interfere constructively or destructively at different angles. This results in the brilliant colors that we see.

6. **Conclusion**:
- The phenomenon responsible for the brilliant colors observed in thin films of oil on water is **interference** of light waves.

### Final Answer:
The phenomenon responsible for the brilliant colors observed in thin films of oil on water when exposed to sunlight is **interference**.

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