In the previous chapter, we mapped magnetic fields and explored the force of magnetic fields on moving charges and currents. In this chapter, we will focus on the cause of magnetic fields (moving charges) and how to calculate fields created by current carrying wires. We will use Ampere's law to calculate the magnetic field and use right-hand rules to predict the direction of the magnetic field from an assembly of current carrying wires. As with Gauss's law, to use Ampere's law we depend on the symmetry of the configuration to make the needed simplifications to the calculations. Once we have expressions for fields from current carrying wires, we can investigate interactions between wires. Since a current carrying wire creates a magnetic field, it can exert a force (Lorentz force: F = q v x B = I L x B) on the current carriers in a nearby wire.