Transformers Flashcards
What does a transformer do?
It changes an alternating voltage from one value to another.
What does a transformer consist of?
Two coils of insulated wire wrapped around an iron core.
How does a transformer work?
The input voltage is connected to the primary coil and the output voltage is taken from the secondary coil.
What are step-up transformers?
Transformers that increase the voltage.
There are more turns on the secondary coil than on the primary coil.
What are step-down transformers?
Transformers that decrease the voltage.
There are more turns on the primary coil than on the secondary coil.
What is the turns ratio transformer equation?
Np/Ns = Vp/Vs
How efficient are transformers?
Transformers are very efficient and we can assume that no energy is wasted at all.
What equation can be derived from the idea that no energy is wasted in a transformer?
Vp x Ip = Vs x Is
Power in = power out
If the secondary coil has twice as many turns of wire as the primary coil, what will the output voltage be?
Twice the input voltage.
What type of current will transformers only work with?
Alternating current.
Why will direct current not work with transformers?
Using direct current will create a magnetic field in the core, but it will not be a changing magnetic field, so no voltage will be induced in the secondary coil.
As voltage is increased in a step-up transformer, what happens to the current? What equation proves this?
Current is decreased in the same proportion.
P = I x V (power = current x voltage) proves this.
Why is the power output of a transformer always less than the power input in reality?
Heat is lost to the environment.
Why is electricity produced by alternating current in power stations?
- It is easy to generate alternating current
2. Transformers will not work with direct current.
What is the system called through which electricity is sent to homes and factories?
The National Grid.
How is electricity carried throughout the grid?
Electricity is carried along aluminium cables suspended between pylons.
Why is aluminium used to carry electricity?
Aluminium has a low density and can be safely suspended from inexpensive, thin pylons.
What is the disadvantage of pylons?
Pylons are an eyesore.
What are the advantages of pylons?
Pylons provide easy access to cables for maintenance and repair.
Transmission using pylons is cheaper than burying cables underground.
Why are transformers used to create a very high voltage?
To minimise energy loss.
What does a very high voltage mean?
A very high voltage means a low current.
This means that there is less heat lost to the environment.
In a power station, before electricity is passed to overhead power lines, what happens?
A step-up transformer at the power station raises the voltage to 400,000 V.
What happens before electricity is supplied to homes and factories?
For homes, a step-down transformer reduces the voltage to 240 V.
For factories, a step-down transformer reduces the voltage to 33,000 V.
If voltage goes up by 16 times, what happens to current?
It goes down by 16 times.
