# Compass Between two wires

## Homework Statement

two wires are parallel to each other,carries current of same magnitude, and the distance between them is 10cm ,, wire A carries current out of the page ,, Wire B carries current into the page ..... A compass is placed at 4 cm from wire A .. Where does the needle point ?

I also would like to know where does the needle will point if the two wires carries same current direction

## Homework Equations

-
same current direction - Attraction
opposite current direction - Repulsion

## The Attempt at a Solution

I drew the magnetic field around each wire(Wire A-Anticlockwise ... Wire B-Clock wise) , but since the field is circular around a straight wire , so I couldnt know where it will point exactly .

gneill
Mentor
I drew the magnetic field around each wire(Wire A-Anticlockwise ... Wire B-Clock wise) , but since the field is circular around a straight wire , so I couldnt know where it will point exactly .
It will be tangent to the circle at any location around the circle.

It will be tangent to the circle at any location around the circle.
so the other wire wont affect the direction of the needle unless the compass was at mid point ?

gneill
Mentor
so the other wire wont affect the direction of the needle unless the compass was at mid point ?
No, the fields from both wires will sum at any given location (superposition principle). Pick a location and sketch the circles centered on each wire that pass though that point. Sketch in the field vector at that point for each wire. Sum the vectors.

No, the fields from both wires will sum at any given location (superposition principle). Pick a location and sketch the circles centered on each wire that pass though that point. Sketch in the field vector at that point for each wire. Sum the vectors.
alright thanks