Short circuit (sc)

SHORT CIRCUIT (SC)

Short circuit between any two points can be defined in terms of a figure. If a circuit element is replaced by a short length of an ideal conductor, the terminals are said to be short circuited

The voltage across the short circuit is always zero regardless of the current through it. The current in the short circuit depends upon the circuit connected to the terminals. Thus, a short circuit is a two- terminal element for which voltage must be zero when the current is not zero.

Mathematically, V(t) = 0, i(t) ≠ 0.

A short length of copper or aluminium wire can be used for short circuiting.

The concept of short circuit can be clearly understood from the following illustrations.

Illustration 1:

Consider the circuit given below. Here, the terminals C and D are short circuited.

i.e., R₂ is short circuited. Between C and D, the resistance is 0. The effective resistance to the source, V₁= R₁ + 0 = R₁

 Current from the source

I₁ = V₁ /  R₁

All this current will flow through the short circuited path.

Note 1: If there is one more short circuit between C and D, the current through each short circuited path is equal to I₁ / 2

2: If there are n short circuit paths between C and D, the current through each path is equal to I₁ / n.

Illustration 2:

Consider circuit in the figure. Between terminals C and D, there are 3 parallel paths. One of them is a short circuit. So all the current flowing through R₁ flows through this short circuit.

It will not flow through R₂ or R₃. Again, between D and E terminals, there is a short circuit. The current through this path is I₁ as shown in the figure. Current through R₅ is I₁.

The total resistance to the source is

= R_AC+ R_CD+ R_DE + R_EB = R₁+0+0+ R₅

= R₁ + R₅

So, I₁ = V / R₁+R₅ {ohm's law}

Note:

1. The resistance R₂, R₃ R₄ are not effective, whatever may be their values. It is because they are short circuited.

2. The current through resistances which are short circuited will always be zero.