Physics A2 · Magnetic fields. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Every current produces a magnetic field. Around a long straight wire the field lines are circles centred on the wire, further apart as you move away. The right-hand grip rule gives the direction: thumb along the current, fingers curl the way the field goes.
A flat circular coil has lines that loop around each side of the coil and pass straight through its centre. Inside a long solenoid the field is strong and uniform, with parallel lines along the axis. Outside, it looks like the field of a bar magnet. A ferrous core makes the field much stronger.
Two parallel wires exert forces on each other, because each wire sits in the field of the other.
Students think the wire with the larger current feels the larger force. The two forces are always equal and opposite. Also, like currents attract, which is the opposite of like charges.
Answer: Towards the east
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