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The value of current (I) flowing in the circuit shown will be :

A single loop with a 24 V source, current I through a 4 ohm resistor (voltage V1, plus at the left end) and a 2 ohm resistor, then a dependent voltage source 5V1 with its minus terminal at the top

  • A.1.51 A
  • B.2.52 A
  • C.1.71 A
  • D.4.72 A

Answer: C

The current has a magnitude of 1.71 A.

Go round the loop in the direction of I. The source gives a rise of 24 V, the resistors drop \(4I\) and \(2I\), and since I enters the dependent source at its negative terminal, that source gives a further rise of \(5V_{1}\). With \(V_{1} = 4I\):

\[ \begin{aligned} 24 + 5V_{1} &= 4I + 2I \\ 24 + 20I &= 6I \\ I &= -\frac{24}{14} \approx -1.71\ \text{A} \end{aligned} \]

The minus sign means the current actually flows against the marked arrow; its size is 1.71 A, which is the value the options list. If the dependent source were taken as opposing the current, the loop would give \(24 = 26I\), or 0.92 A, which is not an option, so the polarity matters.

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