2.2 Electro- magnetism

• The principle of electromagnetism: a current makes a magnetic field
• The magnetic field of a current-carrying conductor (straight wire and coil); the grip rules
• The solenoid, and factors affecting its strength
• Electromagnetic devices (electric bell, relay, magnetic pick-up); troubleshooting

• explain the principle of electromagnetism in electrical technology
• establish the magnetic field pattern of a current-carrying conductor
• construct a solenoid for a given application
• construct an electromagnetic device for a given application
• troubleshoot an electromagnetic circuit in an appliance
• appreciate the importance of electromagnetism in electrical devices and machines

“How are electromagnets made?”

“Why is electromagnetism important in electrical technology?”

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1. Electromagnetism
   40 min · 1 practice tasks · quiz
   The principle that a current produces a magnetic field, the field around a wire and a coil, how an electromagnet and solenoid are made and strengthened, electromagnetic devices like the bell and relay, and why electromagnetism is so important.
2. The principle of electromagnetism
   40 min · 1 practice tasks · quiz
   An electric current always produces a magnetic field; the field appears with the current and vanishes when the current stops.
3. Field of a current-carrying wire
   40 min · 1 practice tasks · quiz
   The magnetic field of a straight wire is concentric circles, stronger near the wire and with more current.
4. The right-hand grip rule
   40 min · 1 practice tasks · quiz
   Direction of the field around a wire by the right-hand grip (and the Maxwell screw rule).
5. Field of a current-carrying coil
   40 min · 1 practice tasks · quiz
   Turns add so a coil acts like a bar magnet with N and S poles; the coil grip rule finds north.
6. The solenoid
   40 min · 1 practice tasks · quiz
   A solenoid is a long, closely wound coil with a strong, almost uniform field inside and poles at the ends.
7. Factors affecting solenoid strength
   40 min · 1 practice tasks · quiz
   More turns, more current, a soft-iron core, and a shorter tight coil make a stronger solenoid; test with clips.
8. Constructing a solenoid
   40 min · 1 practice tasks · quiz
   Wind a solenoid for a stated job (clip lifter or door-bolt pull), test it, and record turns, current and core.
9. Making an electromagnet
   40 min · 1 practice tasks · quiz
   An electromagnet is a solenoid with a soft-iron core: how it is made, why it is stronger, and how it is switched.
10. The motor principle
    40 min · 1 practice tasks · quiz
    A current-carrying conductor in a magnetic field feels a force; Fleming's left-hand rule and F = B I L explain the electric motor.
11. The electric bell
    40 min · 1 practice tasks · quiz
    How the electric bell uses a make-and-break electromagnet to ring, how to construct a simple one, and typical faults.
12. The electromagnetic relay
    40 min · 1 practice tasks · quiz
    A small coil current switches a separate load circuit; car horn and starter examples, construction and isolation.
13. Magnetic pick-up and lifting magnets
    40 min · 1 practice tasks · quiz
    Pick-up coils sense motion in a field; lifting magnets hold steel while current is on. Other coil devices: loudspeaker.
14. Troubleshooting electromagnetic circuits
    40 min · 1 practice tasks · quiz
    A method for bells, relays and coils: source, coil continuity, mechanical armature, heat; symptoms of open, shorted turns and stuck cores.
15. Electromagnetism in devices and machines
    40 min · 1 practice tasks · quiz
    Why electromagnetism is important: switchable magnetism makes motors, generators, transformers, relays, bells and lifting magnets possible.