SAT Subject Physics Practice Question 272: 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 S1 is left in the position shown in the figure but switch S2 is connected to point Y, what is the current through the resistor R?
Correct Answer: A
With switch S2 connected to Point Y and switch S1 left open, only the right-hand half of the pictured circuit is a closed circuit (the battery V1 and the parallel combination of resistors are effectively removed from the circuit in this situation). The total resistance is R + 2R = 3R, so the current in the circuit is I = V2/3R.