Conductance: What is it? (Definition, Units & Formula)

Contents

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Key learnings:

Conductance Definition: Conductance is defined as the capacity of a substance to allow the passage of an electrical current, which is the opposite of resistance.
Measurement Units: The unit of measure for conductance is Siemens, symbolized as ‘S’, which helps quantify how easily electricity flows through a material.
Formula for Conductance: Conductance is determined by taking the reciprocal of resistance. This explains that conductance increases as resistance decreases, highlighting how easily electric current can flow through a material.
Conductance vs. Conductivity: While conductance measures how much current flows through a material, conductivity quantifies how a material reacts to electrical fields.
Practical Applications: Understanding conductance is crucial in fields like agriculture for soil health assessment and in water treatment to maintain aquatic life.

What is Conductance?

Conductance, or electrical conductance, measures a material’s ability to conduct electricity, essentially showing how easily an electrical current can flow through it. It is the opposite of electrical resistance, mathematically expressed 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 quantifies how much current a device generates per unit of applied voltage. Represented by the letter ‘G’, it is the reciprocal of resistance, ‘R’. Ohm’s law, stated as $v=iR$ , helps calculate this by defining R as:

(1) $\begin{align*} R= \frac{v}{i} \end{align*}$

The word conductivity is the opposite of this expression. It is expressed as a current to voltage ratio.

(2) $\begin{align*} G= \frac{i}{v} \end{align*}$

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:

(3) $\begin{align*} G= \frac{1}{R} \end{align*}$

How to calculate Conductance?

To determine conductance, you need the values of resistance, current, voltage, and the material’s conductivity.

For example for a particular circuit element that has a resistance of $1.25\times 10^{3}ohms$ , determine the conductance value. We know

(4) $\begin{align*} G= \frac{1}{R} \end{align*}$

On substituting the value of given R and value of conductance can be obtained as $0.8\times 10^{3} Siemens$

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

(5) $\begin{align*} R= \frac{v}{i} \end{align*}$

Conductance is reciprocal of resistance. So,

(6) $\begin{align*} G= \frac{1}{R} \end{align*}$

(7) $\begin{align*} G= \frac{i}{v} \end{align*}$

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 $\sigma$ is

(8) $\begin{align*} \frac{G= (Area\times\sigma)}{L} \end{align*}$

where $Area=\pi r^{2}$

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 $\sigma$ of iron is $1.03\times10^{7}$ Siemens/m. The area is calculated using $Area=\pi r^{2}$ as $3.14\times 10^{-6}$ . On doing a further substitution, conductance is found to be 324 Siemens.

Conductivity

Conductivity refers to a material’s ability to transfer energy, defining its electromagnetic properties. It measures how much a material influences current flow when exposed to an electric field, often linked to the current’s density created by the field. Conductance of a conductor also depends on factors like shape, size, and a specific property known as its conductivity.

Conductivity is expressed as $\sigma$ 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.

Conductivity vs Conductance

Conductivity, the measure of a material’s ability to conduct electricity, is defined as the ratio of current density to the electric field that drives the current. It indicates how much energy can move through a system, such as an electrical circuit. This property also applies to the transmission of heat and sound.

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.

Applications of Electrical Conductivity Measurement

Electrical Conductivity and Agriculture

Knowing the electrical conductivity of soil is extremely important for the health and growth of crops when it comes to the agricultural industry. Farmers, as well as growers, are often concerned with monitoring soil phosphates, nitrates, calcium, and potassium because these nutrients are essential for successful plant growth.

Checking the soil’s Electrical Conductivity (EC) will help growers keep track of all of the nutrients in their soil. EC can indicate the number of nutrients in the soil and help growers determine if their soil needs more nutrients or if there are too many nutrients. Using sensors for assessing soil’s apparent electrical conductivity (EC) provides a way to overcome these constraints.

Electrical Conductivity and Water Treatment

Electrical Conductivity (EC) plays a major role in different applications of water quality. In wastewater treatment, EC is assessed to ensure that the salinity of wastewater outgoing is equal to the body of water it is discharged into. The release of water which has an extremely high or low salinity can adversely affect the health of aquatic life.

Electrical Conductivity and Electroplating Bath

Conductivity can also impact galvanized waters and is a common check-in industry such as aerospace, automotive, and jewelry. Metal rinse baths are also used to extract residual chemicals from plated items. When this happens, countercurrent rinses help mitigate produced wastewater.

Measuring the conductivity of the plating process at this point decides whether more water is required and needs to be flushed in. Measurements of conductivity can be used to provide useful industry-specific measurements such as total dissolved solids (TDS) and salinity