Chapter 1: Problem 127
Which physical quantity is represented by \(\mathrm{M}^{1} \mathrm{~L}^{3} \mathrm{~T}^{-3} \mathrm{~A}^{-2}\) ? (a) Resistivity (b) Resistance (c) conductance (d) conductivity
Short Answer
Expert verified
The given dimensional formula \(\mathrm{M^{1}L^{3}T^{-3}A^{-2}}\) does not represent any of the given physical quantities (resistivity, resistance, conductance, or conductivity).
Step by step solution
01
(a) Resistivity #
The dimensional formula for resistivity, denoted by \(\rho\), is:
$$\rho = \frac{\mathrm{M}^{0} \mathrm{L}^{3} \mathrm{T}^{-3} \mathrm{A}^{-2}}{\mathrm{M}^{0} \mathrm{L}^{1} \mathrm{T}^{0} \mathrm{A}^{0}} = \mathrm{M}^{0} \mathrm{L}^{3-1} \mathrm{T}^{-3} \mathrm{A}^{-2} = \mathrm{M}^{0} \mathrm{L}^{2} \mathrm{T}^{-3} \mathrm{A}^{-2}$$
02
(b) Resistance #
The dimensional formula for resistance, denoted by R, is:
$$R = \frac{\mathrm{M}^{0} \mathrm{L}^{3} \mathrm{T}^{-3} \mathrm{A}^{-2}}{\mathrm{M}^{0} \mathrm{L}^{2} \mathrm{T}^{0} \mathrm{A}^{0}} = \mathrm{M}^{0} \mathrm{L}^{3-2} \mathrm{T}^{-3} \mathrm{A}^{-2} = \mathrm{M}^{0} \mathrm{L}^{1} \mathrm{T}^{-3} \mathrm{A}^{-2}$$
03
(c) Conductance #
The dimensional formula for conductance, denoted by G, is:
$$ G = \frac{1}{R} \implies G = \mathrm{M}^{0} \mathrm{L}^{-1} \mathrm{T}^{3} \mathrm{A}^{2}$$
04
(d) Conductivity #
The dimensional formula for conductivity, denoted by \(\sigma\), is:
$$ \sigma = \frac{1}{\rho} \implies \sigma = \mathrm{M}^{0} \mathrm{L}^{-2} \mathrm{T}^{3} \mathrm{A}^{2} $$
# Step 2: Compare the given formula with each option #
Now, we will compare the given dimensional formula \(\mathrm{M^{1}L^{3}T^{-3}A^{-2}}\) with the dimensional formulas of the given options.
_resistivity_: \(\mathrm{M^{0}L^{2}T^{-3}A^{-2}}\)
_resistance_: \(\mathrm{M^{0}L^{1}T^{-3}A^{-2}}\)
_conductance_: \(\mathrm{M^{0}L^{-1}T^{3}A^{2}}\)
_conductivity_: \(\mathrm{M^{0}L^{-2}T^{3}A^{2}}\)
None of the given options match with the dimensional formula \(\mathrm{M^{1}L^{3}T^{-3}A^{-2}}\). Therefore, the given dimensional formula does not represent any of the given physical quantities (resistivity, resistance, conductance, or conductivity).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Resistivity
Resistivity is a fundamental property of materials that quantifies how strongly a material opposes the flow of electric current. It is denoted by the symbol \( \rho \) and has the dimensional formula \( \mathrm{M}^{0} \mathrm{L}^{3} \mathrm{T}^{-3} \mathrm{A}^{-2} \div \mathrm{M}^{0} \mathrm{L}^{1} \mathrm{T}^{0} \mathrm{A}^{0} = \mathrm{M}^{0} \mathrm{L}^{2} \mathrm{T}^{-3} \mathrm{A}^{-2} \). Breaking this down:
- Length (L): Indicates the material's structure affects its resistance to current.
- Time (T): Shows the dependence on time-related factors like electron movement.
- Current (A): Represents the amount of electrical charge.
Resistance
Resistance is the measure of how much a conductor opposes the flow of electric current. Symbolized by \( R \), its dimensional formula is \( \mathrm{M}^{0} \mathrm{L}^{1} \mathrm{T}^{-3} \mathrm{A}^{-2} \).
- Length (L): The bulk value contributes to the physical pathway's impact on current flow.
- Current (A): Relates to how electrical charge interacts with the conductor.
Conductance
Conductance is essentially the reciprocal of resistance, denoted by \( G \). Its dimensional formula is \( \mathrm{M}^{0} \mathrm{L}^{-1} \mathrm{T}^{3} \mathrm{A}^{2} \). This property measures the ease with which electric current can flow through a material. Here are a few key points:
- Length (L): Negative dimension indicates it describes a reduction in area-specific opposition.
- Current (A): A higher conductance means more electric charge can pass.
- Time (T): Suggests a relation to time-domain properties like response time.
Conductivity
Conductivity, denoted by \( \sigma \), measures a material's ability to facilitate the flow of electric current, being the inverse of resistivity. Its dimensional formula is \( \mathrm{M}^{0} \mathrm{L}^{-2} \mathrm{T}^{3} \mathrm{A}^{2} \). Conductivity features:
- Length (L): Reflects direct contribution to the flow rate of current, as seen in area-specific measures.
- Time (T): Communicates response time and dependencies on time-varying conditions.
- Current (A): Superior conductivity means carriers like electrons move efficiently.