(a) Draw a ray diagram to show the image formation by a combination of two thin convex
lenses in contact . Obtain the expression for the power of this combination in terms of the
focal lengths of the lenses.
(b) A ray of light passing from air through an equilateral glass prism undergoes minimum
deviation when the angle of incidence is `(3)/(4)^(th)` of the angle of prism . Calculate the speed of ltbRgt light in the prism.

Explanation

### Step-by-Step Solution

#### Part (a): Ray Diagram and Power of Combination of Lenses

1. **Draw the Ray Diagram**:
- Draw two thin convex lenses (L1 and L2) in contact with each other.
- Mark the object (O) placed in front of the first lens (L1).
- Draw the rays from the object passing through L1 and converging to form an image (P).
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