Defination of Ohm's law
Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes this relationship
I = V / R
where I is the current through the conductor in units of amperes, V is the voltage measured across the conductor in units of volts, and R is the resistance of the conductor in units of ohms. Ohm's Law for DC circuits can be stated as three equations
E = IR
I = E/R
R = E/I
When making calculations, compatible units must be used. If the units are other than ohms, amperes (for current), and volts for voltage), then unit conversions should be made before calculations are done. For example, kilohms should be converted to ohms, and microamperes should be converted to amperes.
Formula of Ohms law
Ohms law basically V = I x R, (voltage in volts equals the current in amperes times the resistance in ohms) is the equation in classical mechanics that models the relationship between the electromotive force (battery, power supply, etc.) to push electrons through a medium such as a metals and semiconductors. The electromotive force is a very strong force in fact the strongest known over distances larger than the nucleus of an atom.
The force most people are familiar with comes from a kind of pump such as a battery or generator that uses chemical energy and mechanical rotational momentum that separates charges from one another. The electrons are pushed toward the negative pole and holes, or atoms wanting electrons to the positive pole. When one provides a path between the two poles with a conductor or semiconductor, electrons are forced toward the cloud of electrons that surround metals repelling them toward the positive pole that has a more positive charge. Electrons don’t rush from the negative pole to the positive but rather push the cloud electrons as in a group more like a person pushing in line on the person in front of them that then pushes on the person in front of them, etc.
Like in the line of people, people tend to resist being moved if for no other reason than momentum. The same is true as the electrons’ mass resists a change in their momentum due to the repulsion of similar charges. In various materials, it’s more difficult than others to move an electron than in others. This “resistance” to move is what gives different materials electrical resistance. The movement encountering resistance is like people in the line dragging their feet a bit and thus losing some of the energy to heat.
This loss of energy can be derived using another equation P = V x I (power in Joules/second equals voltage in Volts time current in Amperes) along with Ohm’s law V = I x R substituting for voltage in the power equation. Doing this you get Power = R x I^2. This is the time rate of loss of energy in Joules/second, Joules being the measure of energy.Not all materials let their electrons move without some loss of energy. Those that allow the movement without loss of energy are called superconductors.