A concave lens is cut vertically into two equal parts. What will be the focal length of each plano-concave lens obtained ?

Explanation

To find the focal length of each plano-concave lens obtained by vertically cutting a concave lens into two equal parts, we can follow these steps:

### Step 1: Understand the Original Lens
The original lens is a concave lens, which has a focal length denoted as \( f_1 \). The lensmaker's formula for a lens is given by:

\[ \frac{1}{f} = (\mu - 1) \left( \frac{1}{r_1} - \frac{1}{r_2} \right) \]
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