Tomas says no transformer can supply more power than it takes in. Is Tomas correct?
A laptop charger is warm to the touch after an hour of work.
In earlier grades you saw that energy which seems to vanish can be tracked down. It usually ends up as heat. The charger's warmth is tracked-down energy.
The last lesson's power balance was the ideal: output power equal to input power, never more.
A real transformer does not quite reach the ideal. Some energy becomes heat on the way through.
The coils carry current, and a current heats the wire it flows through.
The core heats too: the changing field drives small circulating currents around inside the iron.
Those small circulating currents in the core are called eddy currents.
That is why the laptop charger is warm to the touch.
How does a real transformer's output power compare with its input power?
A real transformer wastes a little energy as heat. Where does that heat appear?
A transformer takes in 500 W. Can its output power be exactly 500 W?
A real transformer wastes some energy as heat in its coils and core.
No. Its output power is slightly less than 500 W.
A transformer takes in 500 W and gives out 485 W. Where did the rest go?
500 W − 485 W = 15 W
The missing power leaves as heat from the coils and the core.
The other 15 W became heat in the coils and the core.
What are the small circulating currents in a transformer's core called?
A doorbell transformer feels warm after a day plugged in. Why?
A real transformer takes in 300 W. Which could its output power be?
A transformer takes in 90 W, and its secondary delivers 87 W. What happened to the other 3 W?