What is conductance
What is Conductance?
Conductance (also known as electrical conductance) is defined as the potential for a substance to conduct electricity. Conductance is the measure of how easily electrical current (i.e. flow of charge) can pass through a material. Conductance is the inverse (or reciprocal) of electrical resistance, represented as 1/R.
To have a better understanding of conductance, one must recall the resistance of an object. In a qualitative sense, the resistance tells us how difficult it is for an electrical current to pass. The resistance between two points can be defined in the quantitative sense as the difference in voltage that is needed to carry a unit current across the two specified points.
The resistance of an object is represented as the ratio of the voltage across something to the current passing through it. The resistance is measured in Ohms. The conductance of a component is a determination of how quickly current can flow within the component. Conductance is measured in Siemens (S).
Conductance Formula and Measuring Units
In electronics, conductance is a measure of the current generated for a given applied voltage by a circuit device. Typically denoted by the letter G, conductance is resistance reciprocal, R. To define the formula, we need to apply Ohm’s law which states that v = iR from which R can be calculated as
R = v/i ……………………………………………… (1)
The word conductivity is the opposite of this expression. It is expressed as a current to voltage ratio.
G = i/v ……………………………………………. (2)
Conductance is expressed as G and the measuring unit was “mho”. Later after a few years, researchers replaced the unit with “Siemens” which was denoted by the letter S. When looking at resistance vs conductance – conductance is the inverse of resistance (i.e. 1/resistance), as shown below:
G = 1/R …………………………………………………………. (3)
Calculate Conductance?
Conductance can be calculated with the help of the resistance, current, voltage and conductivity.
For example for a particular circuit element that has a resistance of 1.25 x 103 Ω , determine the conductance value. We know
G = 1/R …………………………………………………………. (4)
On substituting the value of given R and value of conductance can be obtained as 0.8 x 103 Siemens
The next example is an electric circuit, in which a 5V input generates a current of 0.3A in a length of wire. According to Ohm’s law V=IR from which resistance can be calculated as
R = v/i ……………………………………………………….(5)
Conductance is reciprocal of resistance. So,
G = 1/R ………………………………………………….. (6)
G = i/v …………………………………………………. (7)
On substituting the values of i and v, one can derive the value of conductance as 0.06 Siemens
Conductance can be calculated from conductivity. Suppose a wire with a round cross-section of radius r and length L is given with known resistivity value of the wire material, conductance G of the wire can be determined. The relationship between G and σ is
…………………………………………… (8)
where Area = πr2
For example, if there is an iron rod with a radius of 0.001 meters and length 0.1 meters, calculate the conductance of the rod. Assume 
Conductivity
Conductivity attributes to the ability of a material to transfer energy and is one of the characteristic property which is used to describe the electromagnetic properties of materials. It quantifies the effect of matter on current flow in response to an electric field. It is also understood as a material property that determines the density of the conductive current in response to an applied electric field. A conductor’s conductance depends on several factors including its form, dimensions and the material’s property called its conductivity.
Conductivity is expressed as and measured as Siemens per meter. The opposite of resistance is conductivity. Since resistance is the opposite of the current flow, conductance is the amount of current a material may carry out. For example, a low-resistance material is highly conductive and vice-versa. Conductivity is also known as specific conductance. There are different types of conductivity namely Electric, Thermal, Ionic and Acoustic.
Difference between Conductivity & Conductance
The degree to which a given material conducts electricity is known as conductivity. It is calculated as the ratio of the current density in the material to the electric field which produces the flow of current. It calculates the amount of energy that can actually move through a system like in the Electrical circuit. The ability of an object to transmit heat, sound or electricity is known as conductivity.
Conductance tells about to what extent an object conducts electricity, expressed in units of Siemens. It is measured as the ratio of the current that flows to the existing potential difference. It depends on the dimensions of the conductor. Conductance refers to the amount of energy transmitted through a material or substance.
SI unit
siemens, S
Expressed in base units
kg-1 m-2 s3 A2
Other commonly used unit(s)
mho (1 mho = 1 Ω-1 = 1 S)
Mathematical expressions
Conductance is related simply to resistance as
G = 1/R
The conductance of a component is related to the electrical conductivity, σ, of the material from which the component is made, by
G = (σ A)/L
where A is the component’s cross-sectional area and L is its length.
Read article – Units of Resistivity
Visit NCERTworld.com for NCERT solutions and Textbook downloads
