Differences between resistance and resistivity

Understanding the differences between resistance and resistivity is very important as they are closely related. This article aims to bring you clarity on resistance and resistivity by comparing each of their properties, definitions and formula.

Introduction

Every object posses some amount of opposition to the flow of electric current. If the object is a conductor, this opposition results in energy loss occurs in the form of heat within them. The property of any object to oppose electric current is known as resistance. The term resistivity is used to quantify resistance. Here are a few key differences between resistance and resistivity. Let’s begin with their definitions.

Definition of resistivity

Electrical resistivity is defined as the measure of opposition of unit volume of an object to electric current flow. To understand this definition better, assume that we have a solid cube of copper with us and we measure resistance between any two opposite faces of the cube using an ohm-meter. Then resistance indicated by the ohm-meter is known as electrical resistivity of copper. The formula of resistivity is:

Where ‘R’ is the resistance of the object, ‘l‘ is the length of the object and ‘A‘ is its area. The SI unit of resistance is Ohm-meter.

Comparison of resistance and resistivity

The differences between resistance and resistivity can be better understood from the following comparison:

Resistance	Resistivity
Resistance is the total opposition of an object to current flow.	Resistivity is a more standardized term to quantify the resistance of an object. It is the amount of resistance offered per cubic meter of an object.
The SI unit of resistance is Ohm.	The SI unit of resistance is Ohm-meter.
SI base unit of resistance is kg.m2·s-3·A-2.	SI base unit of resistivity is kg⋅m3⋅s−3⋅A−2.
Resistance depends on the physical dimensions of the object and its resistivity of the object at a particular temperature.	Resistivity depends on the material and temperature coefficient of the object.
For a particular material of an object at a specific temperature, the resistance varies with the physical dimensions of the object.	For a particular material of an object at a specific temperature, the resistivity remains constant always.
It is represented by the letter ‘R’.	It is represented by the Greek letter ‘ρ’.

Resistance vs Resistivity: Key points to remember:

1. Resistance varies with the size and shape of an object whereas resistivity is a more standardized quantity that remains the same for a specific temperature and material of the object.
2. The SI unit of resistance is Ohm whereas that of resistivity is ohm-meter.
3. Resistance is represented by the letter ‘R’ whereas resistivity is represented by the Greek letter ‘ρ’.
4. The resistance and resistivity of superconductors are zero.

Foot-note: Differences between resistance and resistivity

Resistance and resistivity are very closely related terms that tell how much an object opposes the current flow through them. These terms can be a little confusing in the beginning. Resistance is the total opposition whereas resistivity is the opposition per cubic meter at a specific temperature. Hope this article makes the differences between resistance and resistivity clear to you.

References:

1. Fundamentals of Geophysics, William Lowrie, Cambridge University Press, 20-Sep-2007
2. Physics by Cutnell, John D; Johnson, Kenneth W
3. Principles of Physics, David Halliday, Robert Resnick, Jearl Walker 2014

Read more articles like this:

• Difference between resistance and impedance
• Resistor color code calculator