A Step-Down Transformer. A transformer connected to a 120-V (rms) ac line is to supply 12.0 V (rms) to a portable electronic device. The load resistance in the secondary is 5.00 Ω. (a) What should the ratio of primary to secondary turns of the transformer be?

Video transcript

Hi, everyone. In this practice problem, we're being asked to find a transformer turn ratio or N one divided by N two. We'll have a refrigerator with a step down transformer lowering the voltage from the electrical outlet to a level that the refrigerator can use. The primary of the transformer is plugged into 100 and 20 fold wall socket and is to supply a six fold to the refrigerator. The lower resistance in the secondary is stand oh when the refrigerator is on. And we're being asked to find the transformers term ratio or N one divided by N two ND. Options given are a 25 B five C 10 and D 20. So we want to recall that the formula that we commonly use for a transformer is P two divided by P one to be equals to N two divided by N one. This equation relates the primary and secondary voltages to the primary and secondary number of turns. So what we're interested to find is the transformers turn ratio or N one divided by N two. So we want to rearrange this equation so that we get N one divided by N two which will be P one divided by P two. In the problem statement, it is given that P one or um the primary is going to be plugged into 100 and 20 fold. And we want the P two to be six fold. So we can substitute those two information into our N one divided by N two formula which will then equals to P one which is 120 fault divided by P two, which is six fault and that will come out to a value of 20. So the transformers term ratio or N one divided by N two is going to be 20 that will correspond to option D in our answer choices. So option D will be the answer to this particular practice problem and that'll be it for this video. If you guys still have any sort of confusion, please make sure to check out our adolescent videos on similar topics on our website and that'll be it for this one. Thank you.