Electronic – Voltage across short circuit

short-circuit

We know that current is passed through a circuit if there is a potential difference between the two terminals of the conductor. But in the case of a short circuit, we say that there is no potential difference between the two terminals and a large amount of current is passed through it. It's a violation of Ohm's law. Isn't it wrong to say that there is no potential difference between the terminals?

Best Answer

It's a violation of Ohm's law

Why do you think so? I don't understand where the idea that Ohm's Law is "violated" by an ideal wire (or ideal short-circuit) comes from.

Ohm's Law:

$$V = IR$$

Now, if \$R=0\$, as is the case for an ideal wire, there is zero voltage across for any current through.

Consider the I-V characteristic for an ideal resistor with a large resistance:

enter image description here

Note that the slope of the characteristic is \$\frac{1}{R}\$ and thus, as \$R \rightarrow \infty\$, the slope approaches zero, i.e., the I-V characteristic becomes horizontal through the origin. This is an ideal open circuit; the current is zero for any voltage across.

Now, consider the I-V characteristic for an ideal resistor with a small resistance:

enter image description here

As \$R \rightarrow 0\$, the slope approaches infinity, i.e., the I-V characteristic becomes vertical through the origin. This is an ideal short circuit; the voltage is zero for any current through.

There is no violation of Ohm's Law - the open circuit and short circuit are simply the limits of \$R \rightarrow \infty\$ and \$R \rightarrow 0\$ respectively.

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