- Ohm’s law states that when voltage goes up, current goes up.
- Transformers must follow the rule Voltage1 x Current1 = Voltage2 x
Current2 (Power Conservation). Thus as Voltage2 goes up (by using a
step-up transformer), Current2 goes down.
One equation says that current goes up when voltage goes up, the other says that current goes down. Now, how does this make sense?
Imagine the following thought experiment: we connect a 1 volt AC generator to a 1 ohm resistor and measure the current. By Ohm’s Law, we should get 1 ampere of current. Now imagine we stuck a 1:10 transformer in the circuit, splitting our one circuit into two electrically-separate circuits. If we measured the current in the second circuit we would see that the Ohm's law still holds, we would get 10 volts(remember it's a 1:10 transformer)/1 ohm = 10 amps. Therefore, in accordance with the Ohm's law as voltage increased so did the amperage.
Now is the exciting part. In order to preserve the condition Voltage1 x Current1 = Voltage2 x Current2, the intial circuit (1 volt, 1 amp) immediately starts drawing 100 amps of current!
Therefore, you may say that the current in the second circuit is relatively lower(10 amps) than in the first one(100 amps) but higher when compared to it's previous state.(1 amp)
The initial circuit obeys Ohm’s law too: the transformer acts somewhat like a resistor, whose resistance goes down as the current demand of the right-circuit goes up.
An expanded version of this explanations is presented here