By what angle the mirror must be rotated such that the reflected ray becomes vertical. Let the light ray incident on the plane mirror with an angle of incidence theta with respect to horizontal

Explanation

To solve the problem of determining the angle by which the mirror must be rotated so that the reflected ray becomes vertical, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Initial Setup**:
- A plane mirror is positioned such that a light ray strikes it at an angle \( \theta \) with respect to the horizontal.
- The angle of incidence \( i \) with respect to the normal is \( 90^\circ - \theta \).

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