The rechargeable batteries for a laptop computer need a muchsmaller voltage than

Question

The rechargeable batteries for a laptop computer need a muchsmaller voltage than what a wall socket provides. Therefore, atransformer is plugged into the wall socket and produces thenecessary voltage for charging the batteries.
a) Is the transformer a step-up or a step-down transformer?Explain.
b) Is the current that goes through the batteries greater than,equal to, or smaller than the current coming from the wall socket?Explain.
c) If the transformer has a negligible resistance, is theelectrical power delivered to the batteries greater than, equal to,or less than the power coming from the wall socket? Explain.
d) The batteries of a laptop computer are rates at 9.0 V, and acurrent of 225 mA is used to charge them. The wall socket providesa voltage of 120 V. Determine the turns ratio of thetransformer.
e) What is the current coming from the wall socket?
f) Find the power delivered by the wall socket and the power sentto the batteries.

Explanation / Answer

a,the transformer is step-down because Vs Nsthe current isgreater c,with the ideal transformer the power equals d,the turns ratio Ns/Np=Vs/Vp=9/120=0.075 e,Ip=Vs*Is/Vp=16.875 mA f,P=Ip*Vp=2.025 W

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