What is interference of light waves ? State two essential conditions to observe it.
In Young's double slit experiment, light of wavelength `6000 overset(*)A` is used to get an interference pattern on a screen. The fringe width changes by 1.5 mm when the screen is brought towards the double slit by 50 cm. Find the distance between the two slits.

Explanation

### Step-by-Step Solution

**Part 1: Interference of Light Waves**

1. **Definition of Interference**:
Interference of light waves is the phenomenon that occurs when two or more coherent light waves overlap and combine, resulting in a redistribution of energy. This leads to the formation of bright and dark fringes on a screen, known as an interference pattern.

2. **Essential Conditions for Interference**:
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