A ray of light PQ is incident normally on the hypotenuse of a right angled prism ABC as shown in the diagram given below:
Name an instrument where this action of the prism is used.

Explanation

To solve the question, we need to identify the instrument that utilizes the action of a right-angled prism when a ray of light is incident normally on its hypotenuse. Here’s a step-by-step solution:

### Step 1: Understand the Setup
- We have a right-angled prism ABC, where angle A is 90 degrees.
- A ray of light PQ is incident normally on the hypotenuse AC of the prism.

**Hint:** Recall that "normally" means the light hits the surface at a 90-degree angle, which affects how it refracts.

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