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ttokoro
21-Topaz I
ttokoro21-Topaz I
21-Topaz I
October 23, 2024
Solved

Electrical Engineering Challenge #8

  • October 23, 2024
  • 2 replies
  • 2700 views

"Theory and Problems of Electric Circuits", 4th edition. McGraw-Hill Companies is also very good text I found in Academia.edu.

In chapter 7 it shows the impulse response of RL circuit.

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Mathcad Prime 10 shows it,

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I also stand with Mathcad side. Another is unique problem and answer of this book.

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My Mathcad Prime sheet shows the answer clockwise current by blue line. Red plot is above answer of clockwise direction. Challenge it.

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Best answer by ttokoro

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2 replies

ttokoro
21-Topaz I
ttokoro21-Topaz IAuthor
21-Topaz I
October 27, 2024

"Theory and Problems of Electric Circuits" is 4th edition. Therefore, auther and millions of readers acsept this very good text book. But, Fig. 16-6's answer is wrong. Table 16-2 red one is also wrong. So, some answers are not correct. Using Prime 10 we can solve it correctly.

 

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t.t.
W
Werner_E25-Diamond I
25-Diamond I
October 27, 2024

I don't know what your blue plot i(t) should show, but is definitely not the function i shown a above!

Werner_E_2-1730035480744.png

 

I guess that t=0 is the time when the switch is switched over to position " 2" after it has been 'long enough' at position "1".

 

Given the orientation of the source of voltage and the current arrow, at that time the current should be negative, shouldn't it? As inductivity has no effect after 'long enough' time, i(0) = -50V /25 ohm = - 2 A.

So IMHO the ODE should be

Werner_E_1-1730035148940.png

It may be an orientation confusion. Electrons go from minus to plus, but current from plus to minus.
But I think that that whatever orientation, the sign of i(0) and i(infinity) should be the same. either -2A and -4 A, or +2A and +4A.
So maybe you meant the blue plot in your graphics to be the correct solution?

Anyway, the solution you show as being the one in the book seems to be wrong in any case. Maybe you should contact the publisher.

 

BTW, its a pity that the symbolics still is not able to handle units 😞

    ttokoro
    21-Topaz I
    ttokoro21-Topaz IAuthor
    21-Topaz I
    October 27, 2024

    My point of this thread is the error of this Table. + or - is very confusing if using symbols. 

    L*i(0) is s*L*i(0)/s easy to understand.

     

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    t.t.
    ttokoro
    21-Topaz I
    ttokoro21-Topaz IAuthor
    21-Topaz I
    October 29, 2024

    In the Laplace circuit  Fig.16-4 (b), initial charge Qo makes Qo/C voltage and should be Qo/sC voltage source not Vo/sC.

    To check the Laplace method, Werner_E's ODE method is very usefull becouse it must show the plot of voltage and current responce.

    In this case, ODE of the impulse responce of RC circuit is also good problem.

     

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    "Theory and Problems of Electric Circuits", 4th edition. McGraw-Hill Companies.

    image.png

    "Theory and Problems of Electric Circuits", 4th edition. McGraw-Hill Companies.
    CR Table 7-1(a) has no problem. How to add the impulse's information to odesolve block is a good question for electrical circuit understanding!

     

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    t.t.
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