A long cylindrical bar magnet has a magnetization M = 3000 A/m.What is the equivalent current on the curved surface of the cylinder for 5 cm length of the magnet?
A)10 A
B)15 A
C)100 A
D)150 A
E)None of these is correct.

Question

Quizplus · Accepted Answer

The equivalent current on the curved surface is given by:

$I_{equiv} = M 	imes \pi 	imes d$

where d is the diameter of the cylinder.

For a length of 5 cm, we can assume a small cylinder of the height 5 cm and diameter same as the original cylinder. Then,

$d = 2r = 2\left(\dfrac{5}{100}ight) = 0.1$ m

$I_{equiv} = 3000 	imes \pi 	imes 0.1 = 942.48$ A

However, we need to find the current for only 5 cm length. As the height of the small cylinder is 5 cm, the fraction of current passing through it is:

$\dfrac{5}{h} =\dfrac{5}{20}= 0.25$

Therefore, the equivalent current passing through the small cylinder is:

$I_{equiv, 5cm} = 942.48 	imes 0.25 = 235.62$ A

which is approximately equal to 150 A (Option D).

A Long Cylindrical Bar Magnet Has a Magnetization M =