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Resistor Circuits 1
Open Circuits and Short Circuits
Open Circuits
Current will only flow IN A CIRCUIT. That is, around a continuous path (or multiple paths) from and back to the source of EMF. Any interruption in the circuit, such as an open switch, a break in the wiring, or a component such as a resistor that has gone extremely high resistance will cause current to cease. The EMF will still be present, but voltages and currents around the circuit wil have changed or ceased altogether. We say that the open switch or the fault has caused an OPEN CIRCUIT.
Remember that wherever an open circuit exists, although voltage may be present there will be no current flow through the open circuit section of the circuit. Also, as Power(P) is V x I and the current(I) = 0, no power will be dissipated.
Looking further at the simple circuit we used in "Labelling Voltages and Currents" let´s put some actual voltages and currents in and see what happens under "Open Circuit" conditions.
Use the drop down box below the following diagram to select a number of open circuit conditions that might occur in different parts of the circuit. Notice how the voltages and currents around the circuit change depending on where the break in the circuit (the open circuit) occurs. Checking the voltages around a circuit with a voltmeter, and noticing where the thet differ from what we could expect in a correctly working circuit is one of the main techniques used for tracing a fault in any circuit.
Open Circuit Examples.
The opposite extreme fault condition to having an open circuit is having a component or components go "Short Circuit", which is dealt with here.