The rechargeable batteries for a laptop computer need a much smaller voltage tha

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 271 mA is used to charge them. The wall socket provides a voltage of 120 V. Determine the turns ratio of the transformer. N_s/N_p=What is the current coming from the wall socket? I_p Find the average power delivered by the wall socket and the average power sent to the batteries. provides one model for solving this problem. The maximum strength of the earth's magnetic field is about 6.9times10^-5T near the south magnetic pole. In principle, this field could be used with a rotating coil to generate 60.0-Hz ac electricity. What is the minimum number of turns (area per turn = 0.190 m2) that the coil must have to produce an rms voltage of 120 V?

Explanation / Answer

Ep/Es = Ns/Ns = 9.0 / 120 = 7.5

Ep = IpR , Es =IsR

Ep/Es = IpR/IsR = 7.5

Ip = Is (7.5*10^-2)

Ip = (271*10^-3)*(7.5*10^-2) =20.3A

Pp = IpVp = (20.3*10^-3)(120) = 2.43w

Ps = IsVs = (271*10^-3)(9.0) =2.43w

<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

2(60 Hz) 376.99 rad/s
d/dt (6.9e-5 T)(0.190 m^2)(376.99 rad/s)
Vp 1202 V
E = Nd/dt
N = E / d/dt
N (1202 V ) / [ (6.9e-5 T)(0.190 m^2)(376.99 rad/s) ]
N 2861.42turns >2841 turns

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