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Formative assessment questions for teaching physics

A2L Item 252

  • Description: Identify the circuit that is equivalent to the long term behavior of an RC circuit.
  • Goal: Reason regarding capacitors
  • Source: 283-590 RC equivalent at t infinity
  • Keywords: Electromagnetism, Circuits, Capacitors, Reasoning

The question for students:

Consider the following circuit.

Item252_fig1.gif

The capacitor is uncharged when the switch is closed at t=0. Which circuit is equivalent to this circuit as t approaches infinity?


Commentary for teachers:

Answer

(2) Students often misunderstand the statement that capacitors behave like an open circuit after a long time.

This item is best used in conjunction with the previous one. Both should be asked before discussion of either to reveal whether students just have the behaviors reversed or evidence a more serious problem.