Distinguish between unpolarised and plane polarised light. An unpolarised light is incident on the boundary between two transparent media. State the consition when the reflected wave is totally plane polarised. Find out the expression for the angle of incidence in this case.

Explanation

### Step-by-Step Solution

#### Step 1: Distinguish between Unpolarised and Plane Polarised Light
- **Unpolarised Light**: This type of light consists of waves vibrating in multiple planes perpendicular to the direction of propagation. It does not have a specific orientation of the electric field vector.

- **Plane Polarised Light**: In this type of light, the waves vibrate in a single plane. The electric field vector oscillates in one direction, which can be defined as the plane of polarization.

**Hint**: Remember that unpolarised light can come from natural sources like the sun, while plane polarised light can be produced using filters like polaroids.
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