Which statement is a direct expression of Ohm law for a passive resistor?
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AThe voltage drop across a resistance is proportional to the value of resistance and the amount of current flowing through it
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BThe total resistance of a parallel circuit is less than the value of the smallest resistance
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CThe algebraic sum of voltages in a loop is equal to zero
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DThe algebraic sum of currents entering and leaving a point is equal to zero
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ENone of the above
Answer
Correct Answer: The voltage drop across a resistance is proportional to the value of resistance and the amount of current flowing through it
Explanation
Introduction / Context:Ohm law is the cornerstone of resistive circuit analysis. It relates voltage, current, and resistance in a simple proportional law used in nearly every calculation from bias networks to power estimation.
Given Data / Assumptions:
- Passive, linear resistor behavior in the considered operating range.
- Temperature and self-heating effects are negligible.
- DC or AC steady-state conditions are acceptable for the proportional relation.
Concept / Approach:Ohm law states V = I * R. Therefore, the voltage drop across a resistance is directly proportional to current and proportional to resistance. This is a direct statement of the law. The law enables simple series-parallel reductions and power calculations with P = V * I = I^2 * R = V^2 / R.
Step-by-Step Solution:1) Recall the relation V = I * R.2) Interpret: for a given R, voltage varies linearly with current; for a given I, voltage scales with R.3) Select the statement that explicitly expresses this proportionality.
Verification / Alternative check:Plotting V versus I for a resistor yields a straight line with slope R, confirming the proportional relationship.
Why Other Options Are Wrong:
- Option B: True property of parallels but not Ohm law.
- Option C: This is Kirchhoff Voltage Law, not Ohm law.
- Option D: This is Kirchhoff Current Law, not Ohm law.
- Option E: Incorrect because Option A is correct.
Common Pitfalls:Confusing Ohm law with Kirchhoff laws or network theorems is common. Always tie Ohm law to the element relation of a resistor only.
Final Answer:The voltage drop across a resistance is proportional to the value of resistance and the amount of current flowing through it.