Question A8.7: The current present at a junction in a circuit is shown in F...

Electronic Circuits Fundamentals and Applications

The current present at a junction in a circuit is shown in Fig. A8.3 where $I_1 = 0.1 A, I_2 = 0.25 A$ and $I_3 = 0.3 A$ . Determine the value of the unknown current, $I_x$ .

A8.3

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From Kirchhoff’s Current Law, the algebraic sum of the current at a junction in a circuit is zero. Adopting the convention that current flowing towards the junction is positive and that flowing away from the junction is negative we can construct a formula along the following lines:

0 = -I_x + I _1 -I _2 -I_3

We can re-arrange the equation to make $I_x$ the subject by adding $I_x$ to both sides:

0 + I_x = -I_x + I_x+ I_1 - I_2 - I_3

From which:

I_x = I_1 -I_2 -I_3

Now $I_1 = 0.1 A, I_2 = 0.25 A$ and $I_3 = 0.3 A$
Thus:

$I_x = 0.1 - 0.25 - 0.3 =$ −0.45 A

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