A charging cell phone battery requires a current of 1.60 A and power is dissipat

Question

A charging cell phone battery requires a current of 1.60 A and power is
dissipated in the battery at 7.52 W. Assume that the charger contains
a perfect transformer. a) If the charger is plugged into a standard
wall socket in Philadelphia (120 V AC), determine the voltage
supplied to the battery. b) Determine the current drawn from the wall
by the charger. c) Determine the ratio of the number of primary to
secondary turns within the transformer in the charger and determine
the minimum values of Np and Ns. d) State whether the transformer
is a step-up or a step-down transformer. Justify your answer. Show ALL work!

Explanation / Answer

power dissipated=7.52W=i^2*R=1.60*1.60*R

R=2.9375 ohm

V=i*R=1.6*2.9375=4.7 volt

transformer ratio=120 : 4.7

current drawn from the wall=4.7*1.6/120=0.062666666667 A

(a)the voltage

supplied to the battery is 4.7 volt

(b)the current drawn from the wall by the charger=0.06266666666666667 A

(c)the current drawn from the wall by the charger=1200 : 47

Np/Ns = 4.7/120 = 0.039

(d)transformer is a step-down decause it decreases the voltage

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