Open and Short Circuit questions

circuit analysiscurrentvoltage

I am confused on the terms Open, Short, and Closed when talking about circuits. As far as I know:

  • a) Open circuit means the wires are cut off so there will be no current flow, but there is voltage.
  • b) Closed circuit means the wires are connected so there will be flow of current, but there is no voltage
  • c) Short circuit also refers closed circuit.

Is my knowledge (a,b,c) about the question correct?

There is also another thing which confuses me:

  • d) Voltage is the force that makes the current flow. How can there be current but no voltage or voltage but no current? (from formula: \$V = I \cdot R\$)

Please explain a, b, c and d so it won't bother me anymore if I am going to solve circuits..

Best Answer

For (a,b,c) that's more or less correct. In general, there doesn't have to be a voltage/current just because there is a short/open, there just can't be any voltage in a perfect short and there can't be any current in a perfect open.

Another way to re-word these two terms is that a short circuit has 0 resistance (R=0), and an open circuit has infinite resistance (R=infinity).

So in Ohm's law, \$V = IR\$.

If \$R = 0\$, then \$V = 0\$.

If \$R = \infty\$, then using some mathematical trickery:

$$ I = \lim_{R\rightarrow \infty} \frac{V}{R} = 0 $$

As far as the force analogy goes, if it's useful think about you pushing on a building. Just because you are applying a force doesn't mean the building is going anywhere. These type of analogies tend to break down when dealing with theoretical 0's and infinities, so I wouldn't rely too heavily on them but rather look at the mathematics.

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