Question

A long straight wire in the horizontal plane carries a current of 75 A in north of south direction, magnitude and direction of field B at a point 3 m east of the wire is ______.

Options

• 4 × 10^-6 T, vertical up

• 5 × 10^-6 T, vertical down

• 5 × 10^-6 T, vertical up

• 4 × 10^-6 T, vertical down

Answer 1

A long straight wire in the horizontal plane carries a current of 75 A in north of south direction, magnitude and direction of field B at a point 3 m east of the wire is 5 × 10^-6 T, vertical up.

Explanation:

From Ampere circuital law

`phivec"B".vec"dI"=mu_0"I"_"enc"` 

B × 2πR = `mu_0"I"_"enc"` 

B = `(mu_0"I"_"enc")/(2pi"R")` = 2 × 10^-7 × `75/3`

= 5 × 10^-6 T

According to the screw rule or right hand rule, the direction of the field at the specified point will be vertical up.