Free response questions help the examiner to assess your standard from different angles and to some extent the evaluation will be subjective. But you can rest assured that the questions are so set that they are as specific as practicable. You must be very careful in presenting your answers in respect of free-response questions. Since the words “determine”, “derive”, “calculate”, “ justify”, “explain”, “what is”, “sketch” and “plot” have precise meanings in the AP Physics examination, you must thoroughly understand their significance so that you can give enough details wherever required and refrain from giving unwanted details where they will be sheer waste of time.

Here are two typical free response questions on direct current circuits. The first question is meant for both AP Physics B and C while the second question is meant for AP Physics C only.

_{1}, a 6 Ω resistor R

_{2 }and a 2 µF capacitor C as shown in the figure. A series combination of a 6 Ω resistor R

_{3}and a switch S is connected across the series combination of R

_{2}and C. The switch S is initially open and the battery has been connected for a long time.

(a) Determine the voltage across the capacitor C and the magnitude of the charge on one of its plates.

(b) The switch S is now closed. Determine the voltage across the capacitor C *immediately* after closing the switch S.

(c) Calculate the voltage across the capacitor C a long time after closing the switch S.* *

(d) Calculate the energy stored in the capacitor C a long time after closing the switch S.* *

(e) On closing the switch S, will the energy stored in the capacitor increase, decrease or remain unchanged? Put a tick mark against the correct option

Increase _____ Decrease _____ Remain unchanged _____

Justify your answer.

The above question carries 15 points.

_{1}and S

_{2}are open. The battery has negligible internal resistance.

(a) The switches S_{1} and S_{2} are closed simultaneously. What will be the voltage across the resistor R_{2} immediately after closing the switches S_{1} and S_{2}? Justify your answer.

(b) Determine the current through the resistor R_{2} immediately after closing the switches S_{1} and S_{2}.

(c) A long time after closing the switches S_{1} and S_{2}, the voltage across the resistor R_{1} was found to be 6 V. Calculate the value of the resistor R_{2}.

(d) After a long time the switch S_{1} is opened but the switch S_{2} is retained in the closed condition. Calculate the voltage across the resistor R_{2} at the instant when 0.6 seconds have been elapsed after opening switch S_{1}.

This question carries 15 points.

Try to answer the above questions. I’ll be back shortly with model answers for you.

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