Transformers IGCSE
Transformer power output (V_out x I_out)
= efficiency x power input (eff. x V_in x I_in)
Batteries supply ....
d.c.
Transformers change voltage by ....
electromagnetic induction
What is the normal efficiency of a transformer?
99.9% Efficiency is defined as the ratio of useful power output (VI) to power input (VI)
Power input
= Voltage intput x Current input (primary coil)
useful power output
= Voltage output x Current output (secondary coil)
What is the national grid
A series of transformers and power lines that connect power stations to consumers
How does a transformer work?
An alternating current in the primary coil produces a changing magnetic field (in the core). The secondary coil is a conductor in a changing magnetic field.Its wire turns cuts the lines of magnetic flux and an EMF is induced across the conductor the secondary coil.
What is a transformer?
An electrical device used to change the value of alternating voltage
What are the coils wound on to?
An iron core
What are energy losses in a transformer due to?
Eddy currents are induced in the transformer core, causing heating and resulting in energy losses
What is the iron core made up of to reduce energy losses?
It is made of iron laminations, to reduce eddy currents.
What is a step up transformer?
Less turns on the primary coil than secondary coil, it increases the voltage and decreases the current.
What is a step down transformer?
More turns on the Primary coil than on the secondary coil, it decreases the voltage (and increases the current )
What does a transformer consist of?
Two coils of wire called windings, primary and secondary
The turns to voltage ratio for a transformer is
V1/V2 = N1/N2
What is the only common link between the primary and secondary coil?
a magnetic field
Transformers need ....... to work.
a.c.
What is the input current for a transformer?
a.c.
Examples of where transformers are used.
battery chargers, low voltage power supplies, microwave ovens, etc.
Useful power output = power input
for 100% efficient transformers
electromagnetic induction
production of an e.m.f. across a electrical conductor in a changing magnetic field