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.