The proper exposure time for a photographic print is `20 s` at a distance of `0.6 m` from a `40` candles power lamb.How long will you expose the same print at a distance of `1.2 m` from a `20` candles power lamb?

Explanation

To solve the problem step by step, we will use the concept of intensity of light and the relationship between exposure time, distance, and power of the lamp.

### Step 1: Understand the relationship between intensity, distance, and power
The intensity (I) of light from a point source is given by the formula:
\[ I = \frac{P}{A} \]
where \( P \) is the power of the lamp and \( A \) is the area over which the light is spread. For a point source, the area \( A \) can be expressed in terms of distance \( r \) from the source:
\[ A = 4\pi r^2 \]
Thus, the intensity can also be expressed as:
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