- #1
rajeshmarndi
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I am having problem on understanding the below solution regarding constant of integration.
On integrating an differential equation of RL circuit , for e.g
$$10i + 3\frac{di}{dt} = 50 $$
$$i.e \frac{di}{50-10i} =\frac{dt}{3}$$
Integrate
$$\frac{3}{10} ln(5-i) = t + k $$
At i(0)=0,$$K = - \frac{3}{10}ln 5$$
I get two different value of K.
On substituting the value of K in the equation. I will get different value of i.
Please clarify the mistake. Thanks.
On integrating an differential equation of RL circuit , for e.g
$$10i + 3\frac{di}{dt} = 50 $$
$$i.e \frac{di}{50-10i} =\frac{dt}{3}$$
Integrate
$$\frac{1}{10} \int\frac{1}{5-i} di = \frac{1}{3}∫dt ...(1)$$
$$\frac{1}{10}ln(5-i) = \frac{t}{3} + K$$
Since i(0) = 0,
$$\frac{1}{10}ln(5-0) = 0 + K$$
( I understand since it's an RL circuit equation, I assumed when i=0 , also t=0 )
$$K = \frac{-ln5}{10}$$Now if I do the above solution at (1), as
$$\frac{3}{10} ∫\frac{1}{5-i} di = ∫dt$$
$$\frac{1}{10}ln(5-i) = \frac{t}{3} + K$$
Since i(0) = 0,
$$\frac{1}{10}ln(5-0) = 0 + K$$
( I understand since it's an RL circuit equation, I assumed when i=0 , also t=0 )
$$K = \frac{-ln5}{10}$$Now if I do the above solution at (1), as
$$\frac{3}{10} ∫\frac{1}{5-i} di = ∫dt$$
At i(0)=0,$$K = - \frac{3}{10}ln 5$$
I get two different value of K.
On substituting the value of K in the equation. I will get different value of i.
Please clarify the mistake. Thanks.