# Magnetic field and direction question.

## Homework Statement

Calculate the magnitude and direction of the magnetic field 25cm to the east of a straight vertical wire with a current of 12A downward through the air.

## Homework Equations

B = u(I / 2*pi*r)

## The Attempt at a Solution

Finding the magnitude is simple, but finding the direction is giving me difficulty.

The magnitude is 9.6E-6 T, and the direction is South. How is the direction South?

berkeman
Mentor

## Homework Statement

Calculate the magnitude and direction of the magnetic field 25cm to the east of a straight vertical wire with a current of 12A downward through the air.

## Homework Equations

B = u(I / 2*pi*r)

## The Attempt at a Solution

Finding the magnitude is simple, but finding the direction is giving me difficulty.

The magnitude is 9.6E-6 T, and the direction is South. How is the direction South?

You use the right hand rule to determine the direction. If you grab hold of the wire (figuratively speaking) with your right hand, with your thumb pointing in the direction of the current flow, then your fingers curl around the wire in the same direction that the B field circles the wire.

So grab the wire with your right hand with your thumb pointing down. Seen from above, do your fingers curl in the clockwise or counter-clockwise direction?

berkeman
Mentor

Clockwise, since the current faces downwards.

So the direction for that point (east of the wire) is South because that is the direction the field faces when it connects with the point?

berkeman
Mentor
Clockwise, since the current faces downwards.

So the direction for that point (east of the wire) is South because that is the direction the field faces when it connects with the point?

Correctomundo.