[Physics] Will current pass without any resistance

Question

I've learned that a resistor converts some electrical energy into heat energy while the current flows through it and thus causes a power loss, but what if there's not any resistor in a circuit. Will current still flow?

Answer 1

Short version: Yep. That's what a short circuit is.

Typically, you will get current to flow as long as it has a path with finite resistance (even zero), a voltage difference, and a supply of charge carriers (e.g., electrons). If there really were no resistance in the circuit, the electrons would go around the circuit, and arrive back at the beginning of the circuit with as much energy as the potential difference (the voltage). That final energy is usually what is dissipated as heat or other types of energy by the circuit. But without resistance (or inductance) it won't have a chance to lose the energy, and will return to the voltage source with lots of energy, which will typically screw up the voltage source. This is essentially what a short circuit is.

However, in any realistic circuit (including a short circuit) and with any realistic voltage source, you will always have some resistance, even if you do not have something specifically designed to be a "resistor". For example, even a normal wire has some resistance. That resistance is so low that we usually ignore it, because other things in the circuit usually have far larger resistances, so it's usually a good approximation to ignore the wire. But when it's just the wire, you can't ignore its resistance. Current will flow, and since the resistance is low -- though not zero -- you will just get a really large current. This will heat up the wire just like any resistor (as you know). And typically that will cause problems like melting the wire or its insulation, or just starting a fire.

But suppose you used a perfect superconducting wire. Well even then, any realistic voltage source still has what's called "internal resistance". You need to add the voltage source's internal resistance to the resistance of everything else in the circuit to get the total. Again, this is frequently so low that we just ignore it -- but we can't when the circuit is just a superconducting wire and a voltage source. Of course, any realistic voltage source will also have a limit to the amount of current that it can supply, as Wikipedia will tell you. But if you really minimize the resistance of the total circuit, then you will typically maximize that current.