Electric resistance is a measure of how difficult it is for electric current to flow through a material. Ohm's law states that the electric current flowing through a material is directly proportional to the voltage applied across the material and inversely proportional to the resistance of the material. This means that if the voltage applied across a material is increased, the electric current flowing through the material will also increase, as long as the resistance of the material remains constant.

The unit of electric resistance is the ohm (Ω). Resistance is determined by the material's physical properties, such as its length, cross-sectional area, and resistivity. Materials with higher resistivity have higher resistance, while materials with lower resistivity have lower resistance. Electrical engineers and physicists use the concept of electric resistance in the design and analysis of electrical circuits, electronic devices, and power transmission systems.

Ohm's law and the concept of electric resistance have many real-world applications. For example, electricians use this law to determine the amount of current that will flow through a circuit given a certain voltage and resistance. It is also used in the design of electrical wiring for buildings and homes, as well as in the design of electronic devices such as computers and smartphones. Power companies use the concept of resistance to design power transmission lines with minimal power loss due to resistance.

The formula for determining the electric resistance can be derived from Ohm's law:

\(V\) \(=\) \(I\) \(\cdot\) \(R\)

\(R\): the electric resistance

\(V\): the electric potential

\(I\): the electric current

The SI unit of electric resistance is: \(ohm\text{ }(\Omega)\)