SAT Subject Physics Practice Question 273: Answer and Explanation
The circuit shown contains two switches: S1, which can connect to point X, and S2, which can connect to point Y.
If switch S2 is left in the position shown in the diagram, but switch S1 is connected to point X, what is the current through the resistor R?
Correct Answer: C
With switch S1 connected to Point X and switch S2 left open, only the left-hand half of the pictured circuit is a closed circuit (the battery V2 and resistor of resistance 2R are effectively removed from the circuit in this situation). The parallel combination of resistors is equivalent to a single resistance of R/4, since
So, because the total resistance is R + R/4 = , the current through resistor R is