A single-loop circuit contains an ideal 9.0 V battery and a 6.0 Ω resistor
PHYSICS · Single correct · AP · Physics 2: Algebra-based · Electric Circuits · Electric Circuits
Problem
A single-loop circuit contains an ideal 9.0 V battery and a 6.0 Ω resistor. A student chooses a clockwise traversal that enters the battery through its positive terminal and exits through its negative terminal. The student writes the loop equation −9.0 V + (6.0 Ω)I = 0.
Which of the following best justifies the negative sign on the battery term?
(a) Because the loop direction is the same as the conventional current, the battery emf must be taken as negative to oppose the current.
(b) Entering the battery at its positive terminal and leaving at its negative terminal corresponds to a 9.0V decrease in potential, so the term is written as −9.0V.
(c) Whenever a loop equation starts at a positive terminal, one must assign a negative sign to the battery emf, irrespective of where the exit point is.
(d) The resistor causes a voltage drop of IR, so the battery’s contribution must have the opposite sign; therefore, it is written as −9.0V.