An arrangement of two lenses consists of a converging lens of focal length 40 cm placed coaxially in contact with another lens of unknown focal length. The combination behaves like a diverging lens of focal length 40 cm. Find the power and nature of the second lens.

Explanation

To solve the problem, we need to find the focal length and power of the second lens in a system where a converging lens is in contact with a diverging lens. Here are the steps to find the solution:

### Step 1: Identify the known values
We have:
- Focal length of the converging lens, \( f_1 = +40 \) cm (positive because it is a converging lens).
- The combination of the two lenses behaves like a diverging lens with a focal length of \( f = -40 \) cm (negative because it is a diverging lens).

### Step 2: Use the lens formula for combinations
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