Physics 205B Quiz 5, spring semester 2012
Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Comprehensive Problem 18.113(d)
A 1000 W room heater from Europe that plugs into a 240 V outlet is brought home by a Physics 205B student. The heater is then (somehow) plugged into a 120 V outlet, where it will draw __________ current and use __________ power compared to Europe.
(A) less; less.
(B) less; the same.
(C) less; more.
(D) the same; less.
(E) the same; more.
(F) more; less.
(G) more; the same.
(H) more; more.
Correct answer: (A)
The resistance R of the heater should remain (approximately) constant regardless of where it is plugged in, such that the current used by the heater in the U.S.:
IU.S. = (120 V)/R,
should be less than the current in Europe:
IEurope = (240 V)/R.
The power used by the heater in the U.S.:
PU.S. = (120 V)2/R,
will also be less than the power used in Europe:
PEurope = (240 V)2/R.
Section 30882
Exam code: quiz05Vo7x
(A) : 10 students
(B) : 1 student
(C) : 3 students
(D) : 3 students
(E) : 0 students
(F) : 1 student
(G) : 7 students
(H) : 1 student
Success level: 39%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.38
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