- #1
matthew1991
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Homework Statement
The capacitance of the variable capacitor of a radio can be changed from 100 to 350 pF by turning the dial from 0° to 180°. With the dial set at 180°, the capacitor is connected to a 130 V battery. After charging, the capacitor is disconnected from the battery and the dial is turned to 0°. What is the charge on the capacitor now?
K air= 1.000
K polystyrene= 2.3
Homework Equations
Q=C/V
V/V(sub)0=K
C=kCsub0=k*Epsilon naught*(A/D)
E=Q^2/2C=V^2*C/2=Q*V/2
The Attempt at a Solution
I tried using conservation of energy to find charge by using V^2*C/2=Q6^2/2C, but it was't the right answer.
there is a hint given that says think about what quantity is conserved. I thought energy was always conserved?