# Physics Questions and Answers – Ohm’s Law

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This set of Physics 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

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

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]

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

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

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.