Transformer Physics Example 3

Follow the full solution, then compare it with the other examples linked below.

medium

A phone charger transformer converts

240 \text{ V}

AC to

5 \text{ V}

AC. If the primary coil has

960

turns, how many turns does the secondary coil have?

1
Turns ratio: $\frac{N_s}{N_p} = \frac{V_s}{V_p} = \frac{5}{240} = \frac{1}{48}$ .
2
$N_s = N_p \times \frac{V_s}{V_p} = 960 \times \frac{5}{240} = 960 \times \frac{1}{48} = 20 \text{ turns}$

Answer

N_s = 20 \text{ turns}

A phone charger is a step-down transformer with a large turns ratio. The large reduction from mains voltage to

5 \text{ V}

requires very few secondary turns relative to primary turns.

About Transformer

A device that changes AC voltage using electromagnetic induction between two coils on a shared iron core.

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