Physics quiz quesiton: light bulb power dissipation in circuit

Physics 205B Quiz 5, spring semester 2012
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 18.65(e)

An ideal 12 V emf source is connected to two 1.6 Ω resistors, a 7.0 Ω resistor, and two ideal voltmeters, as shown at right. Which light bulb is brighter?
(A) Bulb 1.
(B) Bulb 2.
(C) (There is a tie, but both bulbs are completely dead.)
(D) (There is a tie, with both bulbs lit.)

Correct answer: (D)

The two light bulbs are in series with each other, such that there is the same amount of current I passing through both. (The voltmeters are ideal and have infinite resistance, such that no current will be diverted away from bulb 2). Thus the power dissipated by the bulbs will be the same:

P = I2*R.

Section 30882
Exam code: quiz05Vo7x
(A) : 12 students
(B) : 1 student
(C) : 1 student
(D) : 12 students

Success level: 46%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.58

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