Unformatted text preview: h inductor immediately AFTER switch is closed IS THE SAME AS
the current through inductor immediately BEFORE switch is closed Immediately before switch is closed: IL = 0 since no battery in loop R3 Calculation
Calculation The switch in the circuit shown has been open for a long time. At t = 0, the switch is closed. R1
V R2
BB L R3 IL(t=0+) = 0 What is the magnitude of I2, the current in R2, immediately after the switch is closed?
V
V
V
I2 =
(A) (B) (C) (D)
I2 =
I2 =
R2 + R3
R1 + R2 + R3
R1
We know IL = 0 immediately after switch is closed
Immediately after switch is closed, circuit looks V
like: I2 = R1
I= VR2 R3
R2 + R3 I R2 V
R1 + R2 + R3 R3 Calculation
Calculation The switch in the circuit shown has been open for a long time. At t = 0, the switch is closed. R1
V R2 I2
BB L R3 I2(t=0+) = V/(R1+R2+R3) IL(t=0+) = 0 What is the magnitude of VL, the voltage across the inductor, immediately after the switch is closed?
R +R RR 3
VL =
VL = 0
VL = V 2
VL = V
(A) (B) (C) (D) (E)V R ( R2 +3 R )
R1
1
2
3 Kirchhoff’s Voltage Law, VLI2 R2 I2 R3 =0 VL = I2 (R2+R3)
VL = V
( R2 + R3 )
R1 + R2 + R3 VL = V R2 + R3
R1 + R2 + R3 Calculation
Calculation The switch in the circuit shown has been open for a long time. At t = 0, the switch is closed.
What is dIL/dt, the time rate of change of the current through the inductor immediately after switch is closed R1
V R2
BB L R3 VL(t=0+) = V(R2+R3)/(R1+R2+R3) dI L V R2 + R3
dI L
dI L V R + R3
=
=
(A) (B) (C) (D) 2
=0
dt
L R1
dt
L R1 + R2 + R3
dt
The time rate of change of current through the inductor (dIL /dt) = VL /L dI L V R2 + R3
=
dt L R1 + R2 + R3 dI L V
=
dt
L Follow Up
Follow Up The switch in the circuit shown has been closed fo r a lo ng tim e . Wh a t is I2, the current through R2 ? (Positive values indicate current flows to the right)...
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 Spring '14
 Trigraph, long time, iL, switch, DI, VL

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