Ohm’s law proportional change — repaired stem: In a fixed-resistance DC circuit, the current is initially 8 mA. If the current is increased to 24 mA with the same resistance, the source voltage must have tripled. Evaluate this claim.

Difficulty: Easy

Correct Answer: Correct

Explanation:


Introduction / Context:
This item originally referenced a “given circuit” without data. Applying the Recovery-First Policy, we minimally repaired the stem by stating the initial current explicitly and assuming a fixed-resistance DC circuit. The concept being tested is the direct proportionality between current and voltage for a constant resistance, as stated by Ohm’s law.


Given Data / Assumptions:

  • Initial current I1 = 8 mA.
  • Final current I2 = 24 mA.
  • Resistance R is constant (temperature and tolerance effects neglected).
  • DC source; wires and contacts ideal for concept.


Concept / Approach:
Ohm’s law gives I = V / R or equivalently V = I * R. With R fixed, voltage and current are directly proportional. Therefore, any multiplicative change in current requires the same multiplicative change in voltage. Tripling the current requires tripling the voltage at constant resistance.


Step-by-Step Solution:

Write V1 = I1 * R and V2 = I2 * R.Form the ratio V2 / V1 = (I2 * R) / (I1 * R) = I2 / I1.Compute I2 / I1 = 24 mA / 8 mA = 3.Conclude V2 / V1 = 3, i.e., the source voltage must have tripled.


Verification / Alternative check:
Numerical example: If R = 1 kΩ, then V1 = 8 mA * 1 kΩ = 8 V and V2 = 24 mA * 1 kΩ = 24 V, confirming a 3x increase. The specific R cancels in the ratio, so the conclusion does not depend on its value.


Why Other Options Are Wrong:

  • Incorrect: Conflicts with direct proportionality at constant resistance.
  • Only correct for AC sources: The proportionality holds for DC and RMS AC in resistive circuits.
  • Only correct if resistance decreases: Resistance is specified constant; no change is required or implied.


Common Pitfalls:
Forgetting to specify that resistance is constant; mixing peak and RMS when dealing with AC; assuming the conclusion depends on a particular resistance value when the ratio makes it independent.


Final Answer:
Correct.

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