It is a concept question. The answer choices for each question are decreases to
ID: 2029013 • Letter: I
Question
It is a concept question. The answer choices for each question aredecreases to zero
decreases but not to zero
stays the same
increases
A capacitor is connected to a battery. A second capacitor is then added to the first one in parallel. As the second capacitor is added, what happens to...
(a) the charge on the first capacitor?
As the two capacitors remain connected, the plates of the second capacitor are slowly pulled further apart. As the plates are pulled apart, what happens to...
(b) the voltage difference across the first capacitor?
(c) the voltage difference across the second capacitor?
(d) the charge on the second capacitor?
The second capacitor is now disconnected from the rest of the circuit. Then its plates are pulled even further apart. Compared to the values after it was disconnected but before the plates were pulled further part, what happens to...
(e) the voltage difference across the second capacitor?
(f) the charge on the second capacitor?
Explanation / Answer
Okay. The first question can be solved by an application of kirchoff's laws: The voltage drop around a closed loop is zero.
1: Make a loop going through the first batter and the first capacitor: Vbattery+ Vcapacitor = 0. This is unchanged by the addition of the second capacitor. Since Q = CV the charge on the first capacitor is unchanged.
2: This is the same idea as the previous problem. The voltage drop across the second capacitor must still be -Vbattery to satisfy Kirchoff's Law. Both b and c are unchanged.
d. V remains the same while C is clearly decreasing since C depends inversely upon distance. Since V = Q/C this means Q has to decrease also.
e. I'm guessing the assumption here is that the capacitor keeps all the charge on it since ideally there is no leakage to the air. In this case Q is constant. So if we pull the plates farther apart C decreases so by Q= CV V must increase.
f.To solve e you had to make the assumption that the charge on the capacitor was constant.
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