Series-aiding sources with series resistors: Two 6 V batteries are connected in series aiding and applied across two 1.2 kΩ resistors connected in series. What is the current through each resistor (steady-state DC)?
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A5 mA
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B10 mA
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C0 A
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D2.5 mA
Answer
Correct Answer: 5 mA
Explanation
Introduction / Context:Series circuits are foundational in basic electrical engineering. When sources are connected series aiding, their voltages algebraically add. In a pure series path, the same current flows through every element. This question reinforces applying Ohm's law to a composite of series sources and series resistors, and it checks that you remember current is identical through each series component.
Given Data / Assumptions:
- Batteries: two sources of 6 V each, connected series aiding.
- Resistors: two resistors of 1.2 kΩ each, connected in series.
- Assume ideal components (no internal resistance), steady DC conditions.
Concept / Approach:Combine series sources by addition and combine series resistors by summation. Then apply Ohm's law I = V / R for the total loop. In a series circuit, that same current passes through each resistor; therefore the computed loop current is the current through each resistor as well.
Step-by-Step Solution:
Total source voltage: V_total = 6 V + 6 V = 12 V.Total resistance: R_total = 1.2 kΩ + 1.2 kΩ = 2.4 kΩ = 2400 Ω.Loop current: I = V_total / R_total = 12 / 2400 A = 0.005 A = 5 mA.Since series current is the same everywhere, each resistor carries 5 mA.Verification / Alternative check:Voltage drops: V1 = I * 1.2 kΩ = 5 mA * 1200 Ω = 6 V; V2 = 6 V. Sum is 12 V, matching the source addition, so KVL is satisfied.
Why Other Options Are Wrong:
- 10 mA: Would require R_total = 1.2 kΩ, not 2.4 kΩ.
- 0 A: Only true for an open circuit, which is not the case here.
- 2.5 mA: Implies an incorrect total resistance or voltage sum.
Common Pitfalls:
- Forgetting that series aiding sources add and series resistors sum.
- Applying the current to only one resistor rather than the entire loop.
Final Answer:5 mA