Correct at 0°C, Ohm’s law

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(a) I = VR
(b) V ∝ I
(c) V = IR
(d) both (b) and (c)

Correct Answer: (d) both (b) and (c)

Explanation

Ohm’s law states that voltage is proportional to current, hence V = IR, provided physical conditions are constant.

Notes for More Information

CONCEPT: Ohm’s Law

  1. Consider a conductor carrying a current I.
  2. Let V be the potential difference applied across the ends of the conductor.
  3. Ohm’s law states that the potential difference across a conductor is directly proportional to the current flowing through it, provided physical conditions remain constant.
  4. Mathematically:



  1. Hence,



  1. Here, R is called the resistance of the conductor.
  2. Resistance depends on:
    • The material of the conductor
    • The length (size) of the conductor
    • The cross-sectional area (shape) of the conductor

LIMITATIONS OF OHM’S LAW

  1. Ohm’s law is valid for a large class of materials, especially metallic conductors.
  2. However, there are certain materials and devices where Ohm’s law does not hold.
  3. Deviations occur due to one or more of the following reasons:

(a) Non-linear V–I relationship

  1. For some materials, V is not proportional to I over the entire range of voltage or current.

(b) Dependence on direction of voltage

  1. The relationship between V and I depends on the sign of V.
  2. Reversing the direction of the applied voltage (keeping magnitude same) does not produce the same current in the opposite direction.

(c) Non-unique V–I relation

  1. The V–I relationship is not unique.
  2. There may be more than one value of voltage V for the same current I.

EXPLANATION: Ohm’s Law

  1. If a conductor carries current I and a voltage V is applied across it, the current is directly proportional to the applied voltage.
  2. This gives the relation:



  1. Therefore, Option (d) is correct.

IMPORTANT CLARIFICATION

  1. It may appear that resistance changes when voltage changes.
  2. This is incorrect.
  3. The resistance of a conductor does not depend on voltage.
  4. Resistance depends only on:
  • Material
  • Shape
  • Size of the conductor
  1. Increasing or decreasing the voltage does not change the resistance, as long as physical conditions (like temperature) remain constant.

KEY TAKEAWAY

  1. Ohm’s law defines a linear relationship between voltage and current.
  2. Resistance is a property of the conductor, not of the applied voltage.



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