Unit 13
Magnetism and induction.
Magnetic fields, the force on a current, charges circling in a field, induction, and the transformer.
Before this unit
The unit, lesson by lesson
Lessons
6 lessons · 31 practice questions · about 2 hours
Magnetic fields
What a magnet does to the space round it: field lines and what they say, two poles that always come as a pair, magnets that attract and repel, what a magnet pulls, and the Earth as a magnet.
Electromagnets
An electric current makes a magnetic field: the field inside a coil, how to work it out, what an iron core adds and where it stops, and which end of the coil is the north pole.
The force on a current
A wire carrying a current in a magnetic field is pushed sideways: which way, how hard, and how two opposite pushes turn the coil of an electric motor.
Charged particles in a magnetic field
A charge moving through a magnetic field feels a force at right angles to its motion, so it moves on a circle: the radius mv/qB, a time per turn that does not depend on speed, the charge-to-mass ratio, and a mass spectrometer that sorts isotopes.
Electromagnetic induction
A changing magnetic field induces a voltage: magnetic flux, Faraday's law, why more turns and faster motion give more voltage, Lenz's law, and alternating and effective voltage.
Transformers and the power grid
Two coils on one core: the turns ratio sets the voltage, the current falls as the voltage rises, a transformer does nothing with direct current, and why power lines run at hundreds of thousands of volts.