Ohm’s law is an important fundamental law of physics and electricity. It was proposed by the German Physicist Georg Simon Ohm.
Ohm’s law states that:
The current flowing through a circuit with certain resistance is directly proportional to the voltage difference across the two points.
Stating in the form of expression, Ohm’s law says:
R= V/I, where V, I and R are the voltage, current, and resistance of the given circuit respectively.
Ohm’s law is popular in all its three forms: V= IR, I = V/R, and R = V/I
In this expression, we need to observe three main terms of electricity: Voltage, Current, and Resistance of an electrical circuit.
Let us understand these terms better here:
It is the path in which various electrical components such as the source of power and the electrical appliances that are working by utilizing the power are connected through an electrical conductor.
Note that current flows only in closed circuits, which means there should be a closed path for the current to flow.
In an electrical circuit, there can be many types of elements: power consuming, power generating, resistances, inductances and capacitances and many such.
Note that Ohm’s law is valid only for electrical circuits that have pure resistance in them.
For current to flow, there must be a difference in potential or electrical charge. For example, take the analogy of water flow from one area to another. Water flows only where there is a difference in the altitudes or pressures between the areas. Otherwise, water does not flow.
Similarly, for the current to flow between them, there should be a difference in the electric potential or charge between them. This difference in charge is said to be the voltage between those two points. The higher the potential difference or voltage between two points. This is what Ohm’s law says.
Current is the flow of electrical charge. We all know that electrons are responsible for the flow of current. When excited due to any form of external energy such as light, heat, magnetism or electrical charge, electrons of certain substances get energized and break their bonds, become free electrons and their charge flows throughout the circuit in which they are connected to. This flow of charge is what constitutes Electrical Current.
Every metal has a certain power....of setting the electric fluid in motion. – Alessandro Volta
It is the nature of every electrical conductor to oppose the free flow of current through it. This is called its Resistance. This is different for every conducting material or conductor and is a property of its parameter called Electrical Resistivity, denoted by the Greek letter, ρ.
The resistance, denoted by R, of a conductor is given by R= ρ x l/A, where l is the length of the conductor and A is the area of the cross section of the conductor.
Besides electrical conductivity, the resistance of a material depends on:
Note: Only resistance varies with the above mentioned parameters, but not the resistivity. Resistivity of a substance is fixed by its inherent nature.
Ohm’s law is not just confined to the calculation of current flowing in an electrical circuit. It also helps in calculating the power utilized by a resistive element in an electrical circuit.
The power P consumed by a resistive element is given by the product of voltage drop across its terminals and the current flowing through it. The unit of power is Watts, represented by the symbol W.
P = V x I, W
From Ohm’s law:
We know that V = I x R,
Power, when multiplied by the time for which it is being utilized, gives the electrical energy consumed. Thus, the electrical energy consumed by an electrical appliance is given by the product of kilowatts (or thousands of watts) multiplied by time in hours.
Next time when you purchase an electrical appliance:
Observe that is marked in kilowatt-hours(kWh). Appliances are rated in kWh because it is easy to work with this unit in day to day life rather than working with thousands and millions of joules.
The common unit of electricity is one kilo-watt hour or 1 kWh. We pay our electricity bill based on how many kilowatt hours our appliances have consumed in a given month. Want to know more about how prices of electricity are fixed and why we end up paying so huge electricity bills some times? Check more facts at our free online Electricity bill calculator.
Georg Simon Ohm, the Father of Ohm’s Law.
Image Source: Wikipedia
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“It is easier to resist at the beginning than at the end.” ― Leonardo da Vinci