## 20101030

### Physics quiz question: comparing potential differences in parallel circuit

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

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 18.21

An ideal 8.0 V emf source is connected to a 1.5 Ω resistor and a 15.5 Ω light bulb. The __________ has the greater potential difference.
(A) 1.5 Ω resistor.
(B) 15.5 Ω light bulb.
(C) (There is a tie.)
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (C)

Kirchhoff's loop rule can be applied to either a complete loop that incorporates the 8.0 V emf with the 1.5 Ω resistor, or another complete loop that incorporates the 8.0 V emf with the 15.5 Ω resistor. As the potential rises and drops in a complete loop must sum to zero, then the potential difference across the 1.5 Ω resistor must be 8.0 V; and the potential difference across the 15.5 Ω resistor must be 8.0 V as well. (This is a consequence of these resistors being connected in parallel to the emf.)

Student responses
Section 70856
(A) : 1 student
(B) : 6 students
(C) : 4 students
(D) : 0 students

Success level: 36%
Discrimination index (Aubrecht & Aubrecht, 1983): 1.00