Magnetic effect of a current — State

State, qualitatively, how the strength of the magnetic field varies around straight wires and solenoids.

Around a straight wire, the magnetic field is strongest close to the wire and becomes progressively weaker with increasing distance from it. For a solenoid, the field is strong and fairly uniform inside the coil, and becomes weaker outside and further from the coil; the field strength can be increased by increasing the current, increasing the number of turns, or adding an iron core.