SAT Subject Physics Practice Question 360: Answer and Explanation
The diagram above shows a battery and a variable resistor set at its midpoint resistance in series with a parallel light circuit. Switch 1 (Sw1) is closed and the light bulbs illuminate. When the variable resistor is moved slightly to the left (L) the bulbs dim a little. When the variable resistor is moved slightly to the right (R) the bulbs brighten slightly. What happens in the circuit when the variable resistor is set all the way to the right?
A. The lights brighten considerably.
B. The total circuit resistance increases.
C. The total circuit current decreases.
D. The total applied voltage increases.
E. The total power used in the circuit increases.
Correct Answer: A
The correct answer is (A). When the variable resistor is changed to the right, the total resistance in the circuit is decreased. More current flows, and the lights brighten.