Calculate the solid angle subtended by the periphery of an area of 1cm² at a point situated symmetrically at a distance of 5 cm from the area.

The correct option is 4 × 10⁻² steradian.

To find the solid angle subtended by a given area at a point, we use the definition of solid angle. The solid angle ($\Omega$) subtended by an area ($A$) at a point situated symmetrically at a distance ($r$) is given by the formula:

$\Omega =\frac{A}{r^2}$

From the given details:
• Area ($A$) = 1 cm²
• Distance ($r$) = 5 cm

Substituting these values into the formula, we get:

$\Omega =\frac{1}{5^2}=\frac{1}{25}$

Calculating the value:

$\Omega =0.04\text{steradian}$

We can express 0.04 in scientific notation as:

$\Omega =4\times {10}^{-2}\text{steradian}$

Therefore, the solid angle subtended is 4 × 10⁻² steradian.