If the power of a lens is 4 dioptres , find its focal length.

Explanation

To find the focal length of a lens given its power, we can use the relationship between power and focal length. Here’s how to solve the problem step by step:

### Step-by-Step Solution:

1. **Understand the Formula**: The power (P) of a lens is defined as the reciprocal of its focal length (F). This can be expressed mathematically as:
\[ P = \frac{1}{F} \]
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