A very long magneti is placed vertically with one pole on the table. A neutral point was found at 20 cm from the pole. What is the pole strength if the vertical component of earth's field is `0.4xx10^(-4)Wb//m^(2)`?

Options

A. 16 A-m
B. 8 A-m
C. 4 A-m
D. none of the

Answer

A

Explanation

At neutral point,
`(mu_(0))/(4pi)xx(m)/(d^(2))=V`
or `10^(-7)xx(m)/((20//100)^(2))`
`=0.4xx10^(-4)`
or `m=(0.4xx10^(-4))/(25xx10^(-7))=16A//m`