Question

The battery charger for an mp3 player contains a step-down transformer with a turns ratio of 1:29, so that the voltage of 120 v available at a wall socket can be used to charge the battery pack or operate the player. what voltage does the secondary coil of the transformer provide?

Answer 1

Transformer contains two coils: primary and secondary. They allow change of voltage to lower or higher value. In first case we have step-down and in second case we have step-up transformer.

Formula used for transformer is:
$\frac{ N_{1} }{N_{2} } = \frac{ V_{1} }{V_{2} }$

Where:
N1 = number of turns on primary coil
N2 = number of turns on secondary coil
V1 = voltage on primary coil
V2 = voltage on secondary coil

In a step-down transformer primary coil has more turns than secondary coil. So the ratio 1:29 means that for each turn on secondary coil we have 29 turns on primary coil.

We can solve the equation for V2:
${V_{2}}=\frac{ V_{1}{N_{2} } }{N_{1} } \\ {V_{2}}=\frac{ 120*{x } }{29x } \\ {V_{2}}=4.14V$

Secondary coil provides voltage of 4.14V.