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posted by  1Anonymous on 11/3/2009 12:33:04 PM  |  status: Closed  |  Earned Karma: 27

Basic Circuits Analysis

Course Textbook Chapter Problem Needs by
N/A N/A N/A N/A 11/3/2009 at 3:00:00 PM
Question Details:
Complete the table   

Find the initial value (0+)
Find the final value
Find the time constant
Write the eq for the quantity
Find the value of 2 time constants
Find t when the quantity is 40% of the initial value t
Find V0(t)
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posted by Tachyon12 on 11/3/2009 2:47:33 PM  |  status: Live
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Response Details:
When switch is closed, the 6mA current passes though 2k and 6k. Using current divider, u get current though 6k is 1.5mA.
Now that will produce a voltage of 9V across the resistor. So, Vo(0) = 9V. Note the capacitor is also charged to 9V.

At t=0, when the switched is thrown open, the capacitor starts discharging though 6k resistor. After some time it will be discharged completely, so no current will be flowing though the resistor. Hence Vo(∞)=0V

Time constant = RC= 60ms
The required equation
 Vo(t) = 9e-t/60
Vo(2RC) =9e-120/60=1.21V

40% of 9 =3.6V

t1=-RClog(3.6/9)= 54ms
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