Transformers Flashcards
Describe the makeup of a basic transformer
Aprimary coil and a secondary coil of
wire wrapped around an iron core
Why is iron used as the core for a transformer?
It is easily magnetised
Explain how a transformer works
● An alternating current flows through the primary coil
● This induces a changing magnetic field in the core
● This changing magnetic field induces an electromagnetic force, which produces current in the secondary coil
Why must the current flowing through the primary coil of a transformer be alternating?
● For current to be induced in the secondary coil, the magnetic field in the core must be continuously changing
● For the magnetic field to be changing, the current in the primary coil must be alternating
What can be said about the electrical power input
and output of a 100% efficient transformer?
The electrical power input is equal to the
electrical power output
Give an equation linking number of turns with p.d. in
transformers
primary p.d./secondary p.d. = primary turns/secondary turns
State the power equation for transformers with a
100% efficiency (using voltage and current).
Vp x Ip =Vs x Is
On a step-down transformer, does the secondary coil
have more or fewer turns?
The secondary coil has fewer turns.
What is an advantage of a step down transformer in
the national grid?
It means that the voltage can be reduced
to a value safe enough to be used in
houses
Why is it important to have step up transformers in
the national grid?
It can increase efficiency.
● For the same power, a higher voltage will lead to
a lower current (P=VxI).
● The lower the current, the less energy that is lost.
● Used for transmission across power lines
How does a step up transformer work?
● The primary coil has fewer turns
● An a.c. current produced a magnetic field in the primary coil
● The iron core passes the magnetic field to the secondary
coil
● The magnetic field induces a higher voltage in the
secondary coil
● Power is conserved, so this produces a lower current
Where are step-up and step-down transformers
used in the national grid?
Step-up transformers are used at power
stations
Step-down transformers are used domestically
