P3.3.2 Transformers Flashcards
Describe a way of creating a current through induction.
A conductor cutting through a magnetic field.
Moving a wire through a magnetic field or moving a magnet through a coil of wire.
How do you increase the current produced by induction?
- Moving the magnet or wire faster
- Using a stronger magnet
- Increasing the number of turns, or loops, on the coil
- Increasing the area of the coil
What type of current does a transformer only work with?
Alternating current.
What does a step-down transformer do?
Reduces the voltage / potential difference of the current.
What does a step-up transformer do?
Increases the voltage / potential difference of the current.
How does a transformer work?
An alternating current passes through the primary coil.
The alternating current produces a magnetic field that continuously changes direction. The soft iron core increases the strength of the magnetic field.
The secondary coil cuts through the changing magnetic field, inducing an alternating current if a circuit is connected to the secondary coil.
How does the number of coils in the secondary coil affect the voltage output?
More coils = higher voltage
Less coils = lower voltage
Same coils = equal voltage
What does the assumption that transformers are 100% efficient mean?
The electrical power output would equal the electrical power input.
What equation relates the voltage of the primary coil to the voltage of the secondary coil?
Vp/Vs = Np/Ns
V = voltage N = number of coils
Where would you expect to find a switch mode transformer?
In the power supplies of electronic devices such as laptop and mobile phone chargers.
What frequency do switch mode transformers run at?
Between 50 - 200 kHz
What size are switch mode transformers?
Small and light
What does a switch mode transformer do?
Changes the voltage (decreases) and converts the alternating current to direct current.
How much power does a switch mode transformer use when no load is applied?
Very little.
Why are switch mode transformers useful for the applications they are designed for?
The devices they are designed for require a voltage less than 230v (UK Grid) - they decrease voltage.
They are small and light - suitable for small appliances such as phone chargers and power supplies.
They use very little power when no load is applied e.g when batteries are not charging.
