A bar magnet of magnetic moment 5.0 A m² has poles 20 cm apart. The pole strength would be

The correct option is 25 A m.

To find the pole strength of the bar magnet, we use the fundamental relationship between the magnetic moment, pole strength, and the magnetic length (distance between the poles) of a bar magnet.

The magnetic moment ($M$) of a bar magnet is given by the formula:
$M=m\times 2l$
where:
• $M$ is the magnetic moment of the magnet,
• $m$ is the pole strength of the magnet, and
• $2l$ is the magnetic length (distance between the two poles).

From the question, we are given:
• Magnetic moment, $M=5.0{\text{A m}}^2$
• Distance between the poles, $2l=20\text{cm}$

First, we convert the distance from centimeters to meters to ensure SI units are consistent:
$2l=20\text{cm}=\frac{20}{100}\text{m}=0.2\text{m}$

Now, we rearrange the magnetic moment formula to solve for the pole strength ($m$):
$m=\frac{M}{2l}$

Substitute the given values into the equation:
$m=\frac{5.0}{0.2}$

Calculate the final value:
$m=25\text{A m}$

Thus, the pole strength of the bar magnet is 25 A m.