Why is a 9v battery capable of producing high current but a tesla coil producing thousands of volts can produce very small current?

Question

By Ohm’s law I = V / R. So high voltage should mean high current for constant resistance? Right? I am very confused how this works. Please explain

In: Physics

Answer 1

> Ohm’s law I = V / R

The point that the other replies seem to be missing is that Ohm’s law in that form *only applies to direct current*. Tesla coils deal with very high frequency alternating current.

When electrical current flows through a coil of wire, it creates a magnetic field. At the same time, a changing magnetic field induces a voltage across the wire. So if the current in the coil is increasing, the magnetic field will induce a voltage which *opposes* the change in current. This property is called *inductance*.

You can still apply Ohms law to AC circuits, but the resistance R has to be replaced by the *impedance* which is a function of frequency. At zero frequency, the impedance is equal to the resistance, but the higher the frequency, the more impedance an inductor will have. Tesla coils typically operate at radio frequencies, upwards of 100MHz.

Also note that while the currents in a Tesla coil are much less than you might think if you just plug the voltage into Ohms law, they are not necessarily small, they may be several amps at least.