Equal series resistors: Will two equal-value resistors in series split the source voltage equally across them (ignoring loading)? Assume an ideal DC source and no additional load connected to the midpoint.
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ATrue
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BFalse
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COnly if the source is an ideal current source
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DOnly when wire resistance is strictly zero
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EOnly in AC circuits with sinusoidal sources
Answer
Correct Answer: True
Explanation
Introduction / Context:Voltage dividers are most intuitive when resistor values are equal. This question checks understanding of proportional division: equal resistances in series produce equal drops from a common current.
Given Data / Assumptions:
- Two resistors R and R in series across a DC source Vs.
- No midpoint loading (infinite input impedance at the tap).
- Wire resistance and source internal resistance are negligible, or included symmetrically.
Concept / Approach:
Using the voltage divider relation Vk = Vs * (Rk / ΣR), if R1 = R2 = R, then ΣR = 2R and each drop is Vs * (R / 2R) = Vs/2. Since the same current flows through both resistors, and their resistances are equal, their power dissipations are equal as well (P = I^2 * R).
Step-by-Step Solution:
Compute current: I = Vs / (R + R) = Vs / (2R).Drop across each: V1 = I * R = (Vs / (2R)) * R = Vs/2; similarly V2 = Vs/2.Confirm energy: P_total = Vs * I; P1 + P2 = I^2 * R + I^2 * R = 2 * I^2 * R, matching source power.Verification / Alternative check:
Example: Vs = 12 V, R1 = R2 = 1 kΩ. Each resistor drops 6 V and dissipates P = 6 V * (6 mA) = 36 mW; total is 72 mW, which equals Vs * I = 12 V * 6 mA.
Why Other Options Are Wrong:
- A current source does not change the equality for equal resistors in series with a defined current; the statement concerns a voltage source divider but still demonstrates equal drops under equal current.
- Nonzero but small wire resistance slightly perturbs symmetry; with the assumption given, equal division holds.
- AC/DC distinction is irrelevant for ideal resistors with no loading; magnitudes divide equally.
Common Pitfalls:
Forgetting the effect of loading at the midpoint: a low-impedance load in parallel with the lower resistor changes the effective resistance and skews the division. Always consider Thevenin equivalent when tapping a divider.
Final Answer:
True