Two coils on an iron core: how a transformer works, step-up and step-down, the turns ratio Vp/Vs = np/ns and power in = power out for an ideal transformer.
What you will learn
- Explain how a transformer changes an alternating p.d.
- Use Vp ÷ Vs = np ÷ ns to find a p.d. or a number of turns
- Use Vp Ip = Vs Is to find a current in an ideal transformer
Two coils, one core
- An alternating current in the primary coil makes a changing magnetic field
- The iron core carries that changing field through the secondary coil
- The changing field induces an alternating p.d. across the secondary coil
There is no wire between the coils: the energy passes through the changing field. A steady d.c. makes a steady field, which induces nothing, so a transformer only works with a.c.
The rest of this lesson and its 9 practice questions are locked.
In this lesson
- Two coils, one core
- The turns ratio
- Power in = power out
- Try it: Check a ratio on the calculator
- Try it: Your first turns ratio
9 practice questions, marked as you go; about 25 minutes in all.
In this unit: Magnetism and electromagnetism
Magnets and field lines, electromagnets, the motor effect and F = BIl, then loudspeakers, generators, microphones and transformers.