Question

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 268 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.

Answer 1

Answer:

(a) 0.075

(b)20.1 mA

(c) 2.412 W

Explanation:

Vs = 9 V, is = 268 mA = 0.268 A

Vp = 120 V

(a) Let the number of turns in primary coil is Np and the number of turns in secondary coil of the transformer is Ns.

Ns / np = Vs / Vp

Ns / Np = 9 / 120

Ns / Np = 3 : 40 = 0.075

(b) Let the current drawn from the wall socket is ip.

Ns/ Np = ip / is

0.075 = ip / 0.268

ip = 0.0201 A = 20.1 mA

(c) Power delivered by the socket = Vp x ip = 120 x 0.0201 = 2.412 W

Power sent to the batteries = Vs x is = 9 x 0.268 = 2.412 W