If a 500-V dc power supply is used to charge a 25-µF capacitor. After the capacitor is fully charged, it is disconnected from the power supply and connected across a 20-mH inductor. The resistance in the circuit is negligible. (a) Find the frequency and period of oscillation of the circuit. (b) Find the capacitor charge and the circuit current 1.6 ms after the inductor and capacitor are connected. Then find for the magnetic and electric energies (c) at and (d) at t= 1.6 ms.

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Example:
A 300-V dc power supply is used to charge a 25-µF capacitor. After the capacitor is fully charged, it is disconnected from
the power supply and connected across a 10-mH inductor. The resistance in the circuit is negligible. (a) Find the frequency
and period of oscillation of the circuit. (b) Find the capacitor charge and the circuit current 1.2 ms after the inductor and
capacitor are connected. Then find for the magnetic and electric energies (c) at and (d) at t = 1.2 ms.
Given:
C = 25 x 106 F
L = 10 x 10³ H
t = 1.2 x 10³ s
(c) Solving for magnetic (UB) and electric (UE) energies
at time t=0.
Solution:
Q²
(7.5 x 10-3 C)²
(a) Solving for angular frequency (w)and period (T)
UB=Li²=0 UE 2C 2(25 × 106 F)
1
@=
LC
(10 x 10-³H) (25 x 10 °F)
(d) Solving for magnetic (UB) and electric (UE)
energies at time t = 1.2 ms.
f =
320 Hz
= 2.03 x 10³ rad/s
(1)
2.03 x 10³ rad
S
UB=Li²(10 x 10-3 H) (-10 A)² = 0.5 J
2π
2π
q² (-5.5 x 10-³ C)²
1
T=
UE
= 0.6 J
3.1 x 10 ³s
f 320 Hz
2C
2(25 X 10 F)
(b) Solving for capacitor charge (q) and circuit current (i)
Q = CVm= (25 x 10-6F) (300 V) = 7.5 x 10-³C
since there is no initial given charge so > = 0. Therefore:
q=Qcos (wt + 4) =(7.5 10-³ C)cos [(2.03 x 10³rad/s) (3.1 x 10-³s) +0] = -5.5 x 10-³ C
i = -wQsin(wt + 4) = -(2.03 x 10³ rad/s) (7.5 10-³C)sin [(2.03 x 10³ rad/s) (3.1 x 10-³s) +0] = -10 A
Activity:
If a 500-V dc power supply is used to charge a 25-µF capacitor. After the capacitor is fully charged, it is disconnected from
the power supply and connected across a 20-mH inductor. The resistance in the circuit is negligible. (a) Find the frequency
and period of oscillation of the circuit. (b) Find the capacitor charge and the circuit current 1.6 ms after the inductor and
capacitor are connected. Then find for the magnetic and electric energies (c) at and (d) at t = 1.6 ms.
-
Transcribed Image Text:Example: A 300-V dc power supply is used to charge a 25-µF capacitor. After the capacitor is fully charged, it is disconnected from the power supply and connected across a 10-mH inductor. The resistance in the circuit is negligible. (a) Find the frequency and period of oscillation of the circuit. (b) Find the capacitor charge and the circuit current 1.2 ms after the inductor and capacitor are connected. Then find for the magnetic and electric energies (c) at and (d) at t = 1.2 ms. Given: C = 25 x 106 F L = 10 x 10³ H t = 1.2 x 10³ s (c) Solving for magnetic (UB) and electric (UE) energies at time t=0. Solution: Q² (7.5 x 10-3 C)² (a) Solving for angular frequency (w)and period (T) UB=Li²=0 UE 2C 2(25 × 106 F) 1 @= LC (10 x 10-³H) (25 x 10 °F) (d) Solving for magnetic (UB) and electric (UE) energies at time t = 1.2 ms. f = 320 Hz = 2.03 x 10³ rad/s (1) 2.03 x 10³ rad S UB=Li²(10 x 10-3 H) (-10 A)² = 0.5 J 2π 2π q² (-5.5 x 10-³ C)² 1 T= UE = 0.6 J 3.1 x 10 ³s f 320 Hz 2C 2(25 X 10 F) (b) Solving for capacitor charge (q) and circuit current (i) Q = CVm= (25 x 10-6F) (300 V) = 7.5 x 10-³C since there is no initial given charge so > = 0. Therefore: q=Qcos (wt + 4) =(7.5 10-³ C)cos [(2.03 x 10³rad/s) (3.1 x 10-³s) +0] = -5.5 x 10-³ C i = -wQsin(wt + 4) = -(2.03 x 10³ rad/s) (7.5 10-³C)sin [(2.03 x 10³ rad/s) (3.1 x 10-³s) +0] = -10 A Activity: If a 500-V dc power supply is used to charge a 25-µF capacitor. After the capacitor is fully charged, it is disconnected from the power supply and connected across a 20-mH inductor. The resistance in the circuit is negligible. (a) Find the frequency and period of oscillation of the circuit. (b) Find the capacitor charge and the circuit current 1.6 ms after the inductor and capacitor are connected. Then find for the magnetic and electric energies (c) at and (d) at t = 1.6 ms. -
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