An ideal transformer with 120 turns in its secondary supplies 12 V at 220 mA to

Question

An ideal transformer with 120 turns in its secondary supplies 12 V at 220 mA to a toy train. The primary is connected across a 120­V wall outlet.
(a) How many turns are in the primary?

(b) What is the primary current?

(c) What power is delivered by the wall outlet?

Need help with problem for understanding purposes, not simply the answer. Please show steps, formulas/equations to use and give explanations where necessary. The professor provided the answers for this problem. Please show steps to come to these answers. Thank you!!!

(a) 1200

(b) 22 Ma

(c) 2.6 W

Explanation / Answer

Fraday law is used in tranformers and also the ferromagnetic properties of an iron core is used to efficiently raise or lower AC voltages..The power cant be raised by a transformer so when the voltatage is increased current decreases and vice versa. Current in the primary coil generates a magnatic field.

Using faradays law

when changing voltage is applied to the primary coil the back emf is generated and its given by faradays law.

Vp=emf=-NpA dB/dt

similaryly induced voltage is given by fradays law

Vs=emf=-NsA dB/dt

Vs/VP =Ns/Np---(1)

using Conservation of energy

VpIp=VsIs-(2)

using 1

a)12/120=120/Np

Np=1200

using 2

b)120*Ip=12*220=22 mA

c)P = VI =12*220 =2.64 W

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