Transformers Flashcards
Transformers use [ ] to change p.d. They only work on [ ]
Electromagnetic induction
AC
What are the 2 types of transformers?
Step-up and step-down
Describe the general structure of a transformer
A primary and secondary coil joined with an iron core
Describe a step-up transformer
They step up the voltage
They have MORE turns on the secondary coil than the primary coil
Describe a step-down transformer
They step down the voltage
They have MORE turns on the primary coil than the secondary coil
Describe how transformers work (4)
1) The primary coil produces a magnetic field which stays within the iron core. This means nearly all of it passes through the secondary coil
2) Because there’s an AC current in the primary coil, the field in the iron core is constantly changing direction
3) This rapidly changing magnetic field is then felt by the secondary coil
4) The changing field induces an alternating p.d across the secondary coil (with the same frq. as the AC in the primary)- electromagnetic induction of a p.d
Describe the constantly changing direction of the AC current in a transformer
100 times/second if it’s at 50Hz
It makes a changing magnetic field
Describe the iron core
It’s purely for transferring the changing magnetic field from the primary coil to the secondary
No electricity flows round it
Step-up: The p.d across the secondary coil is [ ] than the p.d across the primary coil
Greater
Step-down: The p.d across the secondary coil is [ ] than the p.d across the primary coil
less
Why wouldn’t transformers work with DC?
There’d still be a magnetic field in the iron core, but it wouldn’t be constantly changing, so there’d be no induction in the secondary because you need a changing field to induce p.d
What are the equations for transformers?
Vₚ / Vₛ = nₚ / nₛ OR Vₛ / Vₚ = nₛ / nₚ V = p.d (volts, V) n = number of turns ₚ = primary coil ₛ = secondary coil
What is the power equation for transformers?
Power in = power out ( P = I * V ) Therefore VₚIₚ = VₛIₛ V = p.d I = current (A)
What are switch-mode transformers?
They are a type of transformers that operate at higher frequencies than traditional transformers
They usually operate between 50 kHz and 200 kHz
Why are switch-mode transformers better than traditional ones?
They work at higher frequencies, they can be made much lighter and smaller than traditional ones that work from a 50 Hz mains supply
This makes them more useful for mobile phone chargers and power supplies (for laptops)
