TRANSFORMERS⚡️
Transformers are used to increase or decrease the potential difference (voltage) flowing through a wire. Step up transformers increase the potential difference, whereas step down transformers decrease the potential difference.
The key equation to remember here is
POWER = CURRENT X POTENTIAL DIFFERENCE.
Transformers are formed by two independant coils (primary and secondary) of wire coiling round one iron core without touching one another, as the two coils are only connected magnetically, not electrically. (Because they do not touch, transformers are useful for isolating electrical supplies).
You will have to know how they work in I/GCSE Physics...
To work, they need the Primary coil to be connected to an AC (alternating current). The changing current produces a changing magnetic field, which in turn induces an alternating potential difference in the secondary coil.
Consequently, an alternating current is produced in the circuit connected to the secondary coil. This would not occure if a DC (direct current) was supplied to the primary coil.
Calculations🤓
Now, back to the equation. When the potential difference (voltage) is stepped up or down, power remains the same. Therefore, the product of the potential difference and current must still be the same, so the current must also change. For example, if going into the transformer the current is 3 Amps and the Potential difference id 10 Volts, the Power must be 30 Watts. Therefore, if the Potential difference coming out of the tranformer is 5 Volts, the Current must be 5 Amps, as 6x5=30.
The last thing you should remember, is that in a step down transformer, the primary coil will be wound around the core more times than the secondary coil. In a step up transformer, the primary coil will be wound around the core fewer times than the secondary coil. This is also directly proportional to the step up or step down.
For example, if the secondary coil is wrapped around the core twice as many times as the primary coil, the potential difference will also double.
- E.g. if the input potential difference is 6 volts, it will become 12. And, as I explained before, the current will also change so that the power remains the same.
Why transformers?🤷♀️
If you're wondering why we may wish to use a transformer, we can look to the national grid for answers! When flowing through wires to our homes for use (you will have seen electricity pilons, especially in the countryside). If we used a high current here, we would lose a lot of energy, for example by heat and sound. Using a high potential difference and low current prevents this being such a problem.
However, this would be very dangerous in our homes, so a step down transformer is used to decrease the Potential difference (to 230 volts in the UK) and increase the current.
References: https://upload.wikimedia.org/wikipedia/commons/thumb/6/64/Transformer3d_col3.svg/440px-Transformer3d_col3.svg.png
Drafted by Catrina (Physics)