Question

The figure below shows a part of an electric circuit. The current marked I_A​ is:

• A. 1.3 A
• B. 1.0 A
• C. 1.7 A
• D. 3 A

Answer 1

The Correct Option is A

To determine the current I_A, we apply Ohm's Law and the principles of a parallel circuit. Assume the circuit consists of multiple resistors connected in parallel. In such a circuit, the voltage across each resistor is the same, and the total current I_total is the sum of individual currents through each resistor. Given the total current options, we have:

• Conservation of Current: For a parallel circuit, the sum of currents through each parallel branch is equal to the total current entering the network. Thus, I_A = I_total - ΣI_other where ΣI_other is the sum of currents in other branches.
• Ohm's Law: This relates current (I), voltage (V), and resistance (R) as I = V/R. Without specific voltage or resistance, assumptions are made based on given current options.

The correct answer from the given options matches the simplest assumption that fits both conservation and Ohm's law for typical simple test circuits without specific resistances or voltages detailed.

Thus, the most reasonable current is I_A = 1 A.

Answer 2

Applying Kirchhoff's Current Law (KCL) at node A: The sum of currents entering a node is equal to the sum of currents leaving the node.

In this case:

Current entering A: \( 0.2 \, \text{A} + 0.2 \, \text{A} = 0.4 \, \text{A} \)

Current leaving A: \( I_A \)

Therefore: \( 0.4 \, \text{A} = I_A + I_{AB} \)

At node B:

Current entering B: \( I_{AB} + 1.2 \, \text{A} \)

Current leaving B: \( 0.5 \, \text{A} \)

Therefore: \(I_{AB} + 1.2 \, \text{A} = 0.5 \, \text{A} \) which means \( I_{AB} = 0.5 -1.2 = -0.7 A \)

Substituting the value of \(I_{AB}\) into the equaition \( 0.4 \, \text{A} = I_A + I_{AB} \)

Therefore: \( 0.4 = I_A - 0.7 \)

\( I_A = 0.4 + 0.7 = 1.1 A \)