Physics·Electricity and magnetism · NSSCO 5.7.1
Electromagnetism & the d.c. motor
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A magnet is always a magnet — but an electric current can make magnetism you switch on and off at will. In this lesson we discover that every current has a magnetic field: neat circles around a straight wire (found with the right-hand grip rule) and a bar-magnet-shaped field around a coil, or solenoid. We build an electromagnet, meet the electric bell and the relay, then reach the idea that runs the world — the motor effect, where a current-carrying wire in a magnetic field feels a force. We learn Fleming's left-hand rule, watch a coil turn, and put it all together as a real direct-current motor with its clever split-ring commutator.
What you'll learn in this lesson
By the end you should be able to (NSSCO Physics 5.7.1):
- Describe an experiment showing that a current-carrying conductor (a straight wire and a solenoid) has a magnetic field around it
- Sketch the magnetic field around a straight current-carrying wire and around a solenoid, and use the right-hand grip rule to find the direction
- Describe how to build an electromagnet, outline its uses, and explain why soft iron is used for the core
- Explain how the electric bell and the relay use an electromagnet
- Describe and use the relative directions of force, current and magnetic field with Fleming's left-hand rule (the motor effect)
- Explain how a current-carrying coil in a magnetic field experiences a turning effect, and how this turning effect is increased
- Describe the action of a split-ring commutator in a two-pole, single-coil d.c. motor, and the effect of a soft-iron cylinder
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