An IDEAL parallel plate capacitor with plate separation d is connected to a batt
ID: 1591485 • Letter: A
Question
An IDEAL parallel plate capacitor with plate separation d is connected to a battery. The capacitor is fully charged to Q Coulombs and a voltage of V Volts. (C is the capacitance, U is the stored energy, and E is the magnitude of the electric field inside the capacitor.) (For each statement select T True, F False).
A) With the capacitor connected to the battery, decreasing d increases C.
B) With the capacitor connected to the battery, increasing d decreases Q.
C) With the capacitor connected to the battery, increasing d decreases E.
D) After being disconnected from the battery, decreasing d increases U.
Explanation / Answer
Energy in a Capacitor in Joules
E = ½CV² = ½QV = ½Q²/C
Q = CV
Parallel plate cap
C = (A/d) in Farads
is 8.854e-12 F/m
is dielectric constant (vacuum = 1)
A and d are area of plate in m² and separation in m
A)true
With the capacitor connected to the battery, decreasing d increases C.
decreasing d increases C
B) V is fixed, C goes down. Q = CV. Q goes down. TRUE
D) with the battery disconnected, Q is fixed. C decreases with increasing d. This decreases C. With both V and C changing, we need to use U = ½Q²/C. Decreasing C increases U. so FALSE