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
The law you should be considering is the power law P = I x V.
For a given power, higher current implies lower voltage and vice versa. Many circuits are POWER limited or constrained.
EDIT: Think of it this way. You can carry a heavy bucket slowly (low current) up a steep hill ( high voltage) or you can carry that bucket far quicker (more current) up a shallower slope (low voltage)
While Ohm’s Law states a direct relationship between voltage and current for constant resistance, this relationship doesn’t apply in scenarios like Tesla coils where the resistance is not constant. In Tesla coils, the extremely high voltage overcomes the air’s resistance, creating a spark. However, this spark has a very high resistance, limiting the current flow.
The formula that actually matters is P = IV. Or rather, P/I = V. Power is constant here, determined by whatever the electrical supply can provide. So you use a step-up transformer to get the current as close to zero as possible, giving you an utterly bonkers voltage.
In simple terms power has two components, voltage and current. With direct current (DC), the power is the voltage times the current. For a given amount of power, you can have low voltage with high current, or high voltage with low current.
Tesla coils take a modest amount of power and raise the voltage, but at the cost of lowering the current. In the end, the power is the same, but expressed differently.
Soldering irons go the other way, they take a certain amount of power and lower the voltage, but raise the current.
Tesla coils produce very high currents if you short them out. Look at [https://youtu.be/BGD-oSwJv3E?t=828](https://youtu.be/BGD-oSwJv3E?t=828)
A major problem with current and voltage that peek and average is different merriment.
If you for example look at a taser the listing on Wikipedia says [https://en.wikipedia.org/wiki/Taser#Function](https://en.wikipedia.org/wiki/Taser#Function)
>A typical TASER device can operate with a peak voltage of 50 [kilo](https://en.wikipedia.org/wiki/Kilo-)[volts](https://en.wikipedia.org/wiki/Volt) (1200 Volts to the body), an electric current of 1.9 milliamps, at for example 19 100 microsecond pulses per second.[^([35])](https://en.wikipedia.org/wiki/Taser#cite_note-Kroll-35) A supplier quotes a current of 3-4 milliamps.
The voltage and the current do not seem to match Ohm’s law. That is because the voltage is peak voltage and the current is average current. If as listed there is 19 pulses each 100 microseconds long per second the on time is only 19 *100 * 10^-6 = 0.0019 seconds = 1.9 mili seconds on every second.
So if the average current is 1.9 milliamps the current during a pulse is 1.9 *10^-3 /1.9 *10^-3 = 1 amp on average during a pulse. Even in a pulse most of the current is in the beginning.
The power source of a taser is energy stored up in a capacitor or a coil, i am not sure, when the energy is drawn from it the voltage drops. So the taser voltage is not 50 000 volts all the time it is 50 000 volts at the beginning of each pulse.
> 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.
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