Physics quiz question: current through series circuit

Physics 205B Quiz 4, spring semester 2010
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 18.31

An ideal 6.0 V emf source is connected to a 12.0 Ω resistor and a 0.5 Ω light bulb. The current flowing through the light bulb is:
(A) 0.013 A.
(B) 0.48 A.
(C) 2.1 A.
(D) 75 A.

Correct answer (highlight to unhide): (B)

The equivalent resistance of this circuit (resistor and light bulb are in series with the emf) is the sum of these resistances. Thus the current flowing through all parts of this circuit is given by:

I = ΔV/R_eq = (6.0 V)/(0.5 Ω + 12.0 Ω) = (6.0 V)/(12.5 Ω) = 0.48 A.

(Response (A) is 1/(R_eq·ΔV); response (C) is R_eq/ΔV; response (D) is R_eq·ΔV.)

Student responses
Section 31988
(A) : 0 students
(B) : 8 students
(C) : 3 students
(D) : 0 students

Success level: 72%
Discrimination index (Aubrecht & Aubrecht, 1983): 1.00