A transformer uses iron to make sure that all the magnetic flux passing through

Question

A transformer uses iron to make sure that all the magnetic flux passing through the primary (“sending”) coil also goes through the secondary (“receiving”) coil. Use Faradays Law to show that the ratio of the voltages on the primary and the secondary, assuming the resistance of the coils is negligible (in other words, the only voltage across a coil is the induced voltage given by Faraday), is simply the ratio of the number of turns of wire in the primary and secondary. (Hint—it is probably easiest to work backwards: start with the notion of the flux to calculate the voltage on each coil.) If a 5 V transformer for your phone charger has 100 turns of wire on the 120 V coil, how many turns are on the secondary (5 V side)?

Explanation / Answer

Vp/Vs = Np/Ns

120/5=100/Ns

Ns = 100*5/120 = 4 turns

turns on the secondary (5 V side) = 4

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