Recall for a transformer with primary coil number N_p anti secondary coil number

Question

Recall for a transformer with primary coil number N_p anti secondary coil number N_s, that the voltages created depend on the magnetic flux change which is the same on both the secondary and primary side of the transformer. Namely V_s = N_sd phi/dt and V_p = N_pd phi/dt and remember also that the there is essentially no power loss in the transformer so one can use that info to calculate currents in the coils You have a cell phone charger that transforms the house current of 115V to 4.XV dc The secondary coil contains 35 turns and the charger supplies to the phone 800mA. Calculate the following. The number of turns in the in the primary coil? The current in the primary coil? The power in the coils?

Explanation / Answer

For transfromer

Vp/Vs=Np/Ns

Np=(Vp/Vs)*Ns=839 turns (approx)

similarly for current

Ip/Is=Ns/Np

Ip=(Ns/Np)*Is=33.39 mA

power =VpIp=3.84 J

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