Solving Transient Response Homework Statement

AI Thread Summary
The discussion revolves around solving a transient response problem involving a voltage source, a switch, a capacitor, and an inductor. It clarifies that before the switch is closed, the capacitor behaves as an open circuit, and the initial currents i1(0-) and i2(0-) can be calculated based on the steady-state conditions. There is confusion regarding the calculations of i2(0+) and the voltage across the capacitor at t=0-, with participants debating the need for proper notation and the impact of the inductor's behavior when the switch is open. The conversation emphasizes the importance of correctly identifying the time points for calculating derivatives and the voltage across components. The thread concludes with a focus on ensuring accurate computations and clarifying the initial conditions for the circuit analysis.
ranju
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Homework Statement


In given network (voltage source V & switch K) , a steady state is reached with the switch k open .At time t=0 , switch k is closed. Find voltage across C before switch is closed? and i1 &i2 at t=0+.Also values of di1/dt and di2/dt at t=0.

Homework Equations

The Attempt at a Solution


since , before closing the switch steady state has reached . so , capacitor will be open & inductor open. so current i1(0-) will be V/R1+R2 =i1(0+). And current i2(0+) =V/R3.
Now for voltage across capacitor before switch is closed , it'll be i1R2-Ldi1/dt but di1/dt is coming out be zero. so voltage should be i1R2. Also di2/dt is coming out to be zero.at t=0- .. Please check if it is correct or not??
 

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ranju said:
so current i1(0-) will be V/R1+R2 =i1(0+).
I would give only half marks for that, because it's lacking an essential pair of parentheses.

And current i2(0+) =V/R3.
Not correct.
 
NascentOxygen said:
because it's lacking an essential pair of parentheses.
which parantheses you are talking about?
Is the mistake occurring because I did'nt consider that a current is flowing through inductor when the switch was open while finding i2??
 
ranju said:
Is the mistake occurring because I did'nt consider that a current is flowing through inductor when the switch was open while finding i2??
Determine the voltage at t=0+ on each end of R3, take their difference and divide by R3. That will be i2 at that time.
 
at t=0+ , the capacitor will be shorted..! so potential difference across R3 will be potential difference across the inductor's branch..Is'nt it?
i1(0+)R2- Ldi2(0+)/dt.. how we will find di2(0+)/dt..??
 
What is the capacitor voltage at t = 0- ?
 
ranju said:

Homework Statement

:
In given network (voltage source V & switch K) , a steady state is reached with the switch k open .At time t=0 , switch k is closed. Find voltage across C before switch is closed? and i1 &i2 at t=0+.Also values of di1/dt and di2/dt at t=0.[/B]
First, the problem does not define when di1/dt and di2/dt are to be computed. Is it at t0- or t0+?
So for the moment that leaves only i1(0+) and i2(0+), plus VC(0-) to be computed.
 
I will limit my next reply to the verification of those computations only, if they are forthcoming..
 
Last edited:
NascentOxygen said:
What is the capacitor voltage at t = 0- ?
it'll be i1(0-)R2 where i2(0-) = V/R1+R2
 
  • #10
ranju said:
it'll be i1(0-)R2 where i2(0-) = V/R1+R2
With the subscript fixed and an essential pair of parentheses added, that would be correct. :confused:

So what would be the capacitor voltage at t=0+ ?

Meaning the current i2(0+) would be ...?
 
  • #11
sorry , actually I did a mistake in subscript its i1(0-) = V/R1+R2 , i2(0-) will be zero..
 

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