AC Transformers Source: OSHA

Flux Change Creates Emf Rapidly changing field high induced emf unchanging field zero induced emf

How a Transformer Works AC current in the primary coils creates a changing magnetic field. The magnetic flux inside the secondary coils changes Changing flux induces emf in the secondary coils

Potential Proportional to Loops Same flux F through both sets of windings Each loop adds emf Emf’s V are proportional to the number of loops N V1 N1 V2 N2 =

Energy is Conserved Ideally: power in = power out V1I1 = V2I2 Realistic: power in > power out Efficiencies usually around 95%

Transformer Summary Power in  power out  loops  higher V, lower I  loops  lower V, higher I

Question A “step-down” transformer converts input at 120 V to output at 20 V. If the input circuit has 1100 W, how much power is available at the output? 200 W. 660 W. 1100 W. 2400 W.

General Physics L18_Faraday Group Work A transformer with 1000 primary windings converts AC at 110 V (primary) to 220 V (secondary). Which is greater: the voltage in the primary circuit or the voltage in the secondary circuit? Where will the number of loops be greater: in the primary or in the secondary?

Group Work A transformer with 1000 primary windings converts AC at 110 V (primary) to 220 V (secondary). What is the voltage ratio V2/V1? What is the loops ratio N2/N1? How many loops are in the secondary circuit (N2)?

Group Work A transformer with 1000 primary windings converts AC at 110 V (primary) to 220 V (secondary). What is the current ratio I2/I1?

Formulas for Transformers Loops: V1 V2 N1 N2 = Power: V1I1 = V2I2 Potential: V2 = V1 I1 I2 = V1 N2 N1 Current: I2 = I1 V1 V2 = I1 N1 N2

Example A transformer with 5000 primary coils and 100 secondary coils has an input voltage of 50 kV. What is the output voltage? Vout = Vin Nout/Nin = (50 kV)(100/5000) = (50 kV)/50 = 1 kv = 1,000 V