An unpolarised light beam strikes a glass surface at Brewster's angle. Then:

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Accepted Answer

1. **Brewster's Law:** When unpolarised light is incident on the interface of two transparent media at a specific angle known as the polarizing angle or Brewster's angle ($i_p$), the reflected light is completely plane-polarised. The vibration of the electric vector in the reflected ray is perpendicular to the plane of incidence.
2. **Refracted Ray:** At this angle, the reflected and refracted rays are perpendicular to each other. However, the refracted (transmitted) ray is only **partially polarised**, not completely. It retains some components of vibration in the plane of incidence.
3. **Conclusion:** Therefore, at Brewster's angle, the reflected light is completely polarised, while the refracted light is partially polarised.

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