Ohm's Law - Class 12 Physics MCQ

This set of Class 12 Physics Chapter 3 Multiple Choice Questions & Answers (MCQs) focuses on “Ohm’s Law”.

1. Give the SI unit of resistivity.
a) ohm/metre²
b) ohm metre²
c) ohm metre
d) ohm/metre
View Answer

Answer: c
Explanation: Resistivity = \(\frac {(Resistance \, \times \, Area)}{Length}\)
SI unit of resistivity=\(\frac {(ohm \, \times \, metre^2)}{metre}\)
= ohm metre.

2. What is the reciprocal of resistivity of a material called? Give its unit.
a) Conductance, ohm^-1
b) Conductivity, ohm^-1 m^-1
c) Conductance, ohm^-1 m^-1
d) Conductivity, ohm^-1
View Answer

Answer: b
Explanation: Conductivity = \(\frac {1}{Resistivity}\)
SI unit of conductivity = \(\frac {1}{ohm \, meter}\)
= ohm^-1 m^-1.

3. Give the SI unit of current density and its dimensional formula.
a) Am^-2, [A¹L^-2]
b) Am², [A¹L²]
c) Am^-1, [A¹L^-1]
d) Am¹, [A¹L¹]
View Answer

Answer: a
Explanation: Current density is the amount of charge flowing per second through a unit area.
The SI unit of current density is ampere per square metre (Am^-2) and its dimensions are [A¹L^-2].

4. Identify the factor which does not depend on the resistance of a conductor.
a) Nature of material
b) Area of cross-section
c) Length
d) Viscosity
View Answer

Answer: d
Explanation: The resistance of a conductor is directly proportional to its length, inversely proportional to the area of cross-section, and nature of the material. The resistance of the conductor does not depend on viscosity.

5. What is the reciprocal of resistance of a material called? Give its unit.
a) Conductance, ohm^-1
b) Conductivity, ohm^-1 m^-1
c) Conductance, ohm^-1 m^-1
d) Conductivity, ohm^-1
View Answer

Answer: a
Explanation: The conductance of a material is the ease with which electric charges flow through it.
Conductance=\(\frac {1}{Resistance}\).
SI unit of conductance=\(\frac {1}{ohm}\)
=ohm^-1.

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