The rechargeable batteries for a laptop computer need a much smaller voltage than what a wall socket provides. Therefore, a transformer is plugged into the wall socket and produces the necessary voltage for charging the batteries. The batteries are rated at 9.0 V, and a current of 254 mA is used to charge them. The wall socket provides a voltage of 120 V. (a) Determine the turns ratio of the transformer. (b) What is the current coming from the wall socket? (c) Find the average power delivered by the wall socket and the average power sent to the batteries.

Explanation:

primary voltage = 120 V, secondary volt = 9V

Turn ratio = turn in secondary / no of turn in primary

turn in secondary / no of turn in primary  = secondary volt / primary voltage

Turn ratio =  9 / 120

= 3 / 40

Power of secondary = power of primary

Power of secondary = volt x current

= 9 x 254 x 10⁻³

= 2.286 W

power of primary ( wall socket ) = 2.286 W

Current of primary = power / volt

= 2.286 / 120

= 19.05 x 10⁻³ A .

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