At the heart of electric circuit theory, there is a paradox.
A voltage source always maintains a constant specified voltage difference across its terminals.
A short circuit is an electrical connection between two points, forcing the two points to be at the same voltage.
But what would happen if we placed a short circuit directly across a voltage source?
The short circuit will try to force the two terminals to be at the same voltage, whereas the voltage source will try to force the two terminals to have the specified voltage difference.
This is the same thing as asking what voltage we would get if we connected two voltage sources with different voltage values, as shown.
A short circuit across a voltage source is just a special case of this, where one of the two voltage sources happens to be at zero volts.
There are several different ways to attempt to answer these questions.
The first way is to respond by saying that these are illegal circuit connections.
The rules of circuit theory state that you are never supposed to do these types of things.
However, this is not really answering the question of what would happen if we broke the rules and did these things anyway.
A second way of attempting to answer these questions is by saying that the wires are not ideal conductors, but actually have some resistance to them.
Therefore, we can analyze the circuit by replacing the wires with resistors with small resistance values.
However, the problem with this answer is that we could use superconductors.
A superconductor has zero resistance.
Therefore, if we short out the two terminals of a voltage source with a superconductor, or if we use a superconductor to connect two voltage sources with different voltage values, we are back to our paradox.
There is a solution to this paradox, but it comes with a disappointment.
The answer is that it is not physically possible to create an ideal voltage source.
For example, a battery must be mathematically modelled as an ideal voltage source in series with a resistor.
This is not a resistor that we deliberately add, but rather it is part of the internal resistance that is intrinsic to the construction of any battery.
The goal of a good battery is to make this internal resistance as low as possible, but it is physically impossible to make this resistance zero.
This is why the voltage across the terminals of any battery always drops the moment we start drawing current from it.
If we place a superconductor across the terminals of a battery, all of the battery’s voltage will drop across its internal resistance, so that there is a zero voltage drop across the superconductor.
The battery’s internal resistance will determine the amount of current that flows.
Since the battery’s internal resistance is designed to be small, this will result in a very large current when a short circuit is applied, which will cause the battery to heat up and lead to a potentially dangerous situation.
Depending on the type of battery, the battery could catch fire or explode.
If we use superconductors to connect two batteries of different voltages,
the internal resistance inside the two batteries will determine the output voltage at the terminals,
in addition to determining the amount of current that will flow.
As in the previous case, since these resistance values are small,
the current that flows can be very large,
which will heat up the batteries and can create a dangerous situation.
Also, since this setup causes current to try to charge the battery with the smaller voltage,
this will create an especially dangerous situation if this battery was not designed to be rechargeable.
Much more information about electric circuits is available in the other videos on this channel.
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