AP® Physics C: E&M - Simple Circuits - MCQs
Question
Three resistors are connected to a battery as shown in the diagram above. The switch is initially open. When the switch is closed, what happens to the total voltage, current, and resistance
in the circuit?
Voltage Current Resistance
(A) increases increases increases
(B) does not does not does not
change change change
(C) does not decreases increases
change
(D) does not increases decreases
change
(E) decreases decreases decreases
Answer/Explanation
Ans: D
The voltage must stay the same because the battery by definition provides a constant voltage. Closing the switch adds a parallel branch to the network of resistors. Adding a parallel resistor reduces the total resistance. By Ohm’s law, if voltage stays the same and resistance decreases, total current must increase.
Question
In the circuit shown above, what is the current through the 3 Ω resistor?
(A) 0 A
(B) 0.5 A
(C) 1.0 A
(D) 1.5 A
(E) 2.0 A
Answer/Explanation
Ans: E
Assume that the current runs clockwise in the circuit, and use Kirchoff’s loop rule. Start with the 7-V battery and trace the circuit with the current: + 7V − I(3Ω) + 3V − I(2Ω) = 0. Solve for I to get 2.0 A.
Question
A 12-volt storage battery, with an internal resistance of 2Ω, is being charged by a current of 2 amperes as shown in the diagram above. Under these circumstances, a voltmeter connected across the terminals of the battery will read
(A) 4 V (B) 8 V (C) 10 V (D) 12 V (E) 16 V
Answer/Explanation
Ans.E
Solution
Summing the potential differences from left to right gives VT = –12 V – (2 A)(2 Ω) = – 16 V. It is
possible for \(V_{T}>\varepsilon \).