# Will high voltage but low current glow a bulb?

Suppose I increase the voltage supplied to a building from a constant power source substantially by putting a transformer. Doing this would reduce the current substantially as well. So will the building's electronics still work?

• You've gone from a bulb in the title to an entire building in the detail. But that aside, did you really mean a constant power source because if so then I have an answer that's very different to the ones already there (not got time to write it just yet though). If you meant the power supply was a constant voltage source (with negligible source impedance) then see Elio's answer. Jun 23, 2019 at 16:11

$$\def\Ip{I_{\rm pr}} \def\Is{I_{\rm sec}}$$ You're doing a very common mistake. It's totally false that to

increase the voltage supplied to a building from a constant power source substantially by putting a transformer[...] would reduce the current substantially

The effect would be to burn every electrical equipment connected to that building's mains.

You're not alone in holding the false belief that if a transformer increases voltage than it decreases current. Things are rather different. It's true that in an upward transformer

$$V$$(secondary) $$>$$ $$V$$(primary) and $$I$$(secondary) $$<$$ $$I$$(primary).

But if voltages are given, currents are determined by load.

Assume a simple load, a resistor $$R$$. If you connect it to primary source $$V_1$$ the current will be $$I=V_1/R$$. Now install your transformer, say with an upward ratio $$V_2/V_1=k>1$$. If $$R$$ is connected to secondary, current will become $$\Is = V_2/R = k\,V_1/R = k\,I.$$ It will increase, not decrease!

As to primary current you'll have $$\Ip = k\,\Is = k^2 I.$$ Let's compute the dissipated power $$W=I^2 R$$.

• without transformer $$W = V_1^2 / R$$
• with transformer $$W = V_2^2 / R = k^2 V_1^2 / R.$$

If $$k$$ is substantially greater than 1 (say 1.2) the power will increase by a factor $$k^2 = 1.44$$. Very few appliances - if any - would withstand the test.

There are some pieces of electronics that need an alternated current to work, so they would not work anymore with a constant voltage. The electronics that uses a transformer already will work if you can connect it without its transformer and if you can provide the exact voltage they need.