# Sources of Magnetic Fields

### Problems

Problem :

Two wires run parallel to each other, each with a current of 109 esu/sec. If each wire is 100 cm long, and the two wires are separated by a distance of 1 cm, what is the force between the wires?

Problem :

Three wires, each with a current of i , run parallel and go through three corners of a square with sides of length d , as shown below. What is the magnitude and direction of the magnetic field at the other corner?

Three wires run a current into the page. What is the magnetic field at point P ?

Problem :

Compass needles are placed at four points surrounding a current carrying wire, as shown below. In what direction does each needle point?

Compass needles are placed at four points in a plane perpendicular to the wire.

Problem :

What is the force felt by a particle with charge q travelling parallel to a wire with current I , if they are separated by a distance r ?

Problem :

Two parallel wires, both with a current I and length l , are separated by a distance r . A spring with constant k is attached to one of the wires, as shown below. The strength of the magnetic field can be measured by the distance the spring is stretched due to the attraction between the two wires. Assuming that the displacement is small enough that at any time the distance between the two wires can be approximated by r , generate an expression for the displacement of the wire attached to the spring in terms of I , r , l and k .

Two wires, one connected to a spring, shown before the spring is stretched to the force between the wires.

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