Direct Ohm’s law implication — for a fixed-value resistor, if the voltage applied across it increases, how does the current through it change (assuming temperature effects are negligible)?
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AIncreases
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BDecreases
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CStays the same
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DCannot be determined without resistance value
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EReverses direction regardless of polarity
Answer
Correct Answer: Increases
Explanation
Introduction / Context:Ohm’s law gives an immediate relationship between the voltage across a resistor and the current through it. Understanding this proportionality is fundamental to predicting how changes in supply voltage affect branch currents in simple and complex circuits alike.
Given Data / Assumptions:
- Resistor value R is constant and positive.
- Temperature and self-heating effects are negligible for the change considered.
- Polarity is fixed; we are discussing magnitude changes.
Concept / Approach:Ohm’s law states V = I * R. Holding R constant implies I = V / R. Therefore, if V increases, I must increase proportionally. This is the definition of a linear, ohmic element. The exact numeric change requires R, but the qualitative direction (increase) does not.
Step-by-Step Solution:
Start from I = V / R for a fixed R.Consider a higher applied V: numerator increases while denominator is unchanged.Therefore I increases linearly with V.Conclude that current increases when voltage increases across a fixed resistor.Verification / Alternative check:Plot I vs. V: the line I = (1/R) * V has positive slope 1/R. Any movement to the right along the V-axis moves up along the I-axis.
Why Other Options Are Wrong:
- Decreases/Stays the same: Contradicts I = V / R for constant R.
- Cannot be determined: While the exact value needs R, the trend is determined.
- Reverses direction: Direction is set by polarity; magnitude increase does not flip direction.
Common Pitfalls:Confusing constant-current sources (which enforce I) with resistors (which follow Ohm’s law); ignoring that significant heating can change R slightly, but the ideal law remains linear.
Final Answer:Increases