Circuits AP Questions

A battery, a resistor, and a capacitor are wired in a circuit with a switch, as shown in the figure above. The capacitor is initially uncharged, and the switch is open. With the switch open, a voltmeter is connected at various pairs of points in the circuit. For which of the following pairs of points would the voltmeter give a nonzero reading

• a and d

• b and c

• b and d

• c and e

How does the current in lightbulb change, if at all, when the switch is closed, and why?

• It does not change because the closed path through the lightbulbs A, B, and C has not changed

• It increases because the equivalent resistance of parallel lightbulbs C and D is less than the resistance of lightbulb D

• It decreases because the current now passes through both lightbulbs C and D as it travels clockwise around the circuit

• The currents cannot be compared without knowing the values of the resistances.

The switch is now closed to connect points a and b. A voltmeter is connected at points c and d. What is the voltmeter reading after a long time?

• 0 V

• 0.5 V

• 5 V

• 10 V

In the circuit above, the capacitor is initially uncharged. The current through the battery immediately after the switch is closed is 3 A. What is the resistance of resistor ?

• 1 ohm

• 5/4 ohms

• 17/8 ohms

• 4 ohms

In the circuit shown above, the capacitor is initially uncharged. Immediately after the switch is closed, the current in the battery is 2 A. What is the potential difference across the 15 ohm resistor immediately after the switch is closed?

• 0 V

• 22.5 V

• 30 V

• 40 V

When the circuit above is connected, the capacitor is uncharged and switch S is open. The switch is then closed, and after a short time there is a current of 62.5 mA in the capacitor branch. What is the current through the 200 ohm resistor at that instant?

• 12.5 mA

• 37.5 mA

• 62.5 mA

• 75 mA

The figure shows a loop consisting of a set of horizontal, frictionless metal rails connected to a resistor. A metal bar is in contact with the rails, creating a closed circuit. The apparatus is located in a constant uniform magnetic field pointing out of the page. The bar moves to the right on the rails, and as a result a current is generated in the circuit. Which of the following are true of this situation? Select two answers.

• The induced emf depends on the instantaneous flux through the loop.

• The current in the circuit depends on the speed at which the bar moves.

• A nonzero external force is required to keep the bar moving to the right.

• There is no energy dissipation in the system as the bar moves.

At the instant shown above, a sphere with charge +Q is moving vertically downward parallel to a vertical wire carrying an upward current I. Which of the following indicate two forces that constitute an interacting force pair? Select two answers.

• The rightward force on the sphere due to the wire and the downward force on the sphere due to Earth

• The rightward force on the sphere due to the wire and the leftward force on the wire due to the sphere

• The downward force on the sphere due to Earth and the upward force on the sphere due to air resistance

• The downward force on the sphere due to Earth and the upward force on Earth due to the sphere