Meaning and mechanism
Alternating current in the primary coil changes the magnetic flux in the iron core and induces an EMF in the secondary coil. Energy can be transferred without a direct wire connection between the coils.
If the rate of current change passing through each surface of the coil is the same, the induced voltage is larger in the coil with more turns. Increasing the voltage results in a smaller output current for the same power output.
Relationships and conditions
An ideal transformer obeys V₂/V₁=N₂/N₁, and input and output power are equal. With efficiency η, Pout=ηPin; voltage ratio and power-transfer efficiency are different quantities.
Constant direct current does not produce continually changing magnetic flux in steady state. Actual transformer behavior is affected by core saturation, leakage flux, and winding losses.
What to observe in the simulation
In an ideal transformer voltage follows the turns ratio and input power equals output power.
DC input current, overheating and switching transients are not modeled. Efficiency losses affect input power only. Experiment on screen; do not reproduce this with real power supplies, outlets or high voltage.
Key relationships and symbols
V₂/V₁ = N₂/N₁ · Pout = ηPin
| Symbol | Meaning | Unit |
|---|---|---|
| N₁, N₂ | Primary and secondary turns | trial |
| V₁, V₂ | Voltage across each coil | V |
| η | Power-transfer efficiency | 0~1 |
Worked example
What input power is needed for 1.152 W output at 90% efficiency?
1.28 W
Common misconceptions
- It is not the case that, if a voltage was increased using a transformer, a new power is created that is larger than the input.