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It is our policy not to do people's homework for them - so have a go, and show your working.They are asking for a transformer that steps down from 240V (the input, available from your wall plug in the UK or Australia, connected to the Primary of the transformer) to 24V AC (the Secondary output that may power a motor or low-voltage lighting, for example).However, to a first approximation, a step-up transformer can also be used as a step-down transformer. If you were studying electrical engineering, there are considerations like the amount of insulation you might use, or slight allowances you might make for magnetisation current or internal resistance. But for a physics question like this appears to be, you can ignore any subtle design differences between step-down and step-up transformers.
I drew a step-down transformer for the problem. When I checked the answer provided for the question, I saw that a step-up transformer have been drawn for the problem. A small note was added " in the diagram, there should be more turns in the primary than in the secondary coil ( the diagram should be change to a step-down transformer) and the turns ratio should be 10 if that is done".If the question is asked the other way round, that is if the 24 V becomes the primary voltage and 240 V becomes the secondary voltage, should I draw step-down transformer and add a small note telling them that there should be more turns in the secondary coil than there is in the primary coil to make it a step-up transformer and the turns ratio will become just as they have done?
Draw a thick vertical line, maybe 20 mm long, to represent the iron core of the transformer. On the left hand side of this draw the primary coil, coils are often represented as a curly line, spring like. Next to this write something like "Primary, 2400turns". Draw another coil on the right hand side of the core line and write next to this "Secondary, 240 turns".The ratio of the transformer needed to reduce 240Volts to 24Volts is ten to one ie 10:1. The numbers I have chosen for the turns are arbitrary but in your case must have a ratio of ten (primary) to one (secondary). With 240Volts applied to the primary 24Volts will appear on the secondary.