4.4 Magnetism and electromagnetic induction

• Magnetization and demagnetization
• Magnetic fields and field patterns
• Introduction to electromagnetic induction
• Factors affecting the magnitude of induced e.m.f.
• Applications of electromagnetic induction

• describe the methods of magnetization and demagnetization in soft iron
• describe the magnetic field patterns around a magnet
• describe induced e.m.f.
• perform an experiment on electromagnetic induction
• explain factors affecting the magnitude of induced e.m.f.
• appreciate the applications of electromagnetic induction in day-to-day life

“How is the study of electromagnetic induction important in our daily life?”

“Where does the electricity in the wires of a house actually come from?”

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1. Magnets, magnetisation and magnetic fields
   40 min · 1 practice tasks · quiz
   How a piece of steel becomes a magnet, how to destroy one, and the shape of the field around it.
2. Electromagnetic induction and where it matters
   40 min · 2 practice tasks · quiz
   How movement makes electricity, what makes the effect larger, and why almost all the world's power depends on it.
3. Soft iron magnetises and demagnetises easily
   40 min · 1 practice tasks · quiz
   Soft iron is for devices that must switch; steel is for magnets that must last.
4. Magnetising by stroking
   40 min · 1 practice tasks · quiz
   A steel needle stroked one way with one pole becomes a magnet; the finishing end is the opposite pole.
5. Electrical magnetisation and demagnetisation
   40 min · 1 practice tasks · quiz
   Direct current in a solenoid magnetises; alternating current, with slow withdrawal, demagnetises.
6. The field around a bar magnet
   40 min · 1 practice tasks · quiz
   Field lines run north to south outside the magnet, never cross, and crowd at the poles.
7. Two magnets: unlike poles, like poles, neutral point
   40 min · 1 practice tasks · quiz
   Unlike poles pull field lines across; like poles push them apart and leave a dead spot in the middle.
8. The compass and the Earth's magnetic field
   40 min · 1 practice tasks · quiz
   A compass needle is a magnet that lines up with the Earth's field, pointing towards geographic north.
9. Fridge magnets and other everyday magnets
   40 min · 1 practice tasks · quiz
   Permanent magnets hold, catch, speak and seal; electromagnets switch. Both sit in Kenyan homes and workshops.
10. Faraday and induced e.m.f.
    40 min · 1 practice tasks · quiz
    In 1831 Faraday showed that a changing magnetic field through a circuit produces an electromotive force.
11. The magnet-and-coil experiment
    40 min · 1 practice tasks · quiz
    Push, hold, pull: the galvanometer kicks, sits at zero, then kicks the other way. Relative motion is what matters.
12. Factors affecting the size of the induced e.m.f.
    40 min · 1 practice tasks · quiz
    Faster motion, more turns, a stronger magnet, a larger area and an iron core all increase the induced e.m.f.
13. How a generator works
    40 min · 1 practice tasks · quiz
    A generator keeps a coil and a magnetic field moving relative to each other so an e.m.f. is induced continuously.
14. How a transformer works
    40 min · 1 practice tasks · quiz
    A changing current in one coil induces an e.m.f. in another coil on the same iron core, changing the voltage of an a.c. supply.
15. KPLC, transformers and electricity in Kenya
    40 min · 1 practice tasks · quiz
    Power is generated, stepped up for the long wires, moved by Kenya Power, then stepped down for homes and industry.