The diagram shows part of a phone charger used at a community repair workshop. A transformer changes the 230 V alternating voltage from the mains before the...
Question 1 Report
The diagram shows part of a phone charger used at a community repair workshop. A transformer changes the 230 V alternating voltage from the mains before the charger electronics supply a battery. The primary coil has 1200 turns and the secondary coil has 60 turns. The transformer has an iron core and is inside a plastic box.
(a) State the type of voltage supplied to the primary coil. [1]
(b) Explain why the voltage in the secondary coil is much smaller than the voltage in the primary coil. [2]
(c) Calculate the secondary voltage. [2]
Answer Details
(a) The primary coil is supplied with an alternating voltage, or a.c. [1]
(b) The secondary coil has far fewer turns than the primary coil. [1] Transformer voltage is proportional to number of turns, so this is a step-down transformer and the secondary voltage is much smaller. [1]
(c) Use the transformer equation:
\[\frac{V_s}{V_p}=\frac{N_s}{N_p}\]
\[\frac{V_s}{230}=\frac{60}{1200}\]
\[V_s=230\times\frac{60}{1200}=11.5\text{ V}\]
The secondary voltage is 11.5 V. [2]
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