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Open circuit

I am wondering how to perform KVL on an open circuit. For V_s = 10V, I have determined the V across R2 to be 10 Ohms but am confused about R3.

The algebraic sum of the voltages around any closed loop in a circuit is equal to zero.

Is the voltage across R3 then 0 V?

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2 Answers 2

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Current into an open stub is zero (assuming nothing is radiated or arcing) so the voltage across R3 is zero.

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Two questions here:

How to perform Kirchhoff's Voltage Law on an open circuit?

Answer: You can't. KVL has to have closed loops to work. You can create a theoretical closed loop, if you'd like, by making a connection between nodes 5 and 4 that is an infinitely large resistor. That might help if you want to see what KVL would say would happen (it will say there is zero current through R3). It is probably easier to think about this using KCL. KCL is true at every node. KCL at node 4 says that current through R3 has to be zero.

Second question:

Is the voltage across R3 then 0 V?

Yes - if the current through it is zero, then the voltage is 0 times R3.

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