Cuesta College, San Luis Obispo, CA
An ideal 6.0 V emf source is connected to an ammeter, a resistor, a light bulb, and an open switch. When the switch is closed, determine whether the ammeter reading (in amps) will decrease, increase, or remain the same, and explain why.
Show your work and explain your reasoning using Kirchhoff's rules, Ohm's law, and properties of ammeters. Solution and grading rubric:
- p:
Correct. Discusses/demonstrates how ammeter reading will increase when the switch is closed because:- when the switch is open, the equivalent resistance is 3.0 Ω, and the ammeter will read the current of this circuit I = εeq/Req = (6.0 V)/(3.0 Ω) = 2.0 A;
- when the switch is closed, no current will flow through the 0.5 Ω resistor (flowing only through the zero resistance path of the closed switch), such that the equivalent resistance decreases to 2.5 Ω, such that the ammeter will read a higher amount of current in this circuit I = εeq/Req = (6.0 V)/(2.5 Ω) = 2.4 A.
- r:
As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. - t:
Nearly correct, but argument has conceptual errors, or is incomplete. - v:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some attempt at applying properties of Kirchhoff's rules, Ohm's law, and properties of ammeters. - x:
Implementation/application of ideas, but credit given for effort rather than merit. No clear attempt at systematically applying Kirchhoff's rules, Ohm's law, and properties of ammeters. - y:
Irrelevant discussion/effectively blank. - z:
Blank.
Sections 30882, 30883
Exam code: midterm02u7aH
p: 20 students
r: 4 students
t: 10 students
v: 6 students
x: 1 student
y: 0 students
z: 0 students
A sample "p" response (from student 1001):
Another sample "p" response (from student 1810):
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