A capacitor is completely charged with 650 nC by a voltage source that has 275 V
ID: 1532725 • Letter: A
Question
A capacitor is completely charged with 650 nC by a voltage source that has 275 V. What is its capacitance? Now the plates of the charged capacitor are pulled apart with the voltage source still connected. Incorrect The charge on the plates increases. Incorrect The capacitance increases. Incorrect The energy stored in the capacitor increases. Incorrect The voltage drop between the plates increases. Correct: None of the above. The initial air gap of the capacitor above was 5 mm. What is the stored energy if the air gap is now 14 mm?Explanation / Answer
a) use, C = Q/V
= 650*10^-9/275
= 2.36*10^-9 F
b) None of them
c) initial energy stored, Ui = (1/2)*C*V^2
= (1/2)*2.36*10^-9*275^2
= 8.92*10^-5 J
As the distance between the plates increases capacitnace decreases.
so, Energy stored also decreases.
Uf = Ui*(5/14)
= 8.92*10^-5*(5/14)
= 3.18*10^-5 J
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