I would like to say that this is my first post here. I had a test in my circuit class and this was one of the questions (bellow). Can someone explain me as to WHY the 2ohm resistor is "shorted out" ?? to my knowledge the answer would have been 6 in series with 2 , the total // with 6 , the total // with 6 again. Thanks in advance and sorry for the stupid question

 

The 2kΩ resistor is said to be shorted out because it has a connection directly across it. (Can you see the connection?)

The connection has no resistance, so no voltage will ever appear across the resistor and the resistor will therefore pass no current. The 2kΩ is effectively eliminated from the circuit.

 

wow i simply "forgot" the notion of how current will always go choose a path with least resistance ! Thank for the quick reply sir !

 

All you need is two tools:

Series Resistance Calculation:

\(R_T = R_1 + R_2 + ...\)

Parallel Resistance Calculation:

\(R_T = \frac{1}{\frac{1}{R1} + \frac{1}{R2} + ...}\)

Then just look at your schematic and simplify resistors, simple as that. If you see two series, simplify it to one resistor and continue. If you see two parallel resistors (or more) simplify those and continue. As Thevenin's theorem states, any complex network can be simplified to a voltage source in series with a resistor.

 

Choose the path of least resistance is at best approximately right. Better: In a parallel connection the current divides so the potential across each path is the same.