Homework Help: Where do i start from?

1. Nov 1, 2007

cwtliew

1. The problem statement, all variables and given/known data

a long straight wire lying along the x-axis carries current I flowing in the +x direction. A second long straight wire lying along the y-axis carries current I/2 in the +y direction.
where is their combined magnetic field zero?

2. Relevant equations

Ampere's Law/biot-savart law

3. The attempt at a solution

where do i begin??
pls help.thanks.

2. Nov 1, 2007

learningphysics

What is the magnetic field due to a current of wire?

Look at each of the quadrants in the xyplane.... examine the direction of fields due to each of the two wires.... in which quadrants are they in the same direction? in which quadrants are they in the opposite direction...

now within the quadrants where the fields are in opposite directions... you need the magnitude of the two fields to be equal (so that they cancel each other out)...

take an aribtrary point (x,y)... what is the field at this point due to the first wire... and due to the second wire... set the two fields equal... solve for y in terms of x.