What is Ohms Law?
Introduction to ohm's law
Georg Simon Ohm was born in 1787 in Erlangen, Germany. He taught mathematics in local schools and performed experiments in physics, trying to master the principles behind electromagnetism. Later, in 1826, he published papers on the way circuits conducted heat in Fourier's studies. In May 1827, Ohm described the relationship between electromotive force, current, and resistance later known as Ohm’s law. Gradually, the term Ohm was adopted as the unit of electrical resistance in 1872.
What is Ohm’s Law?
Ohm's Law states that the current flowing through a conductor is directly proportional to the potential difference applied across its ends, provided the temperature and other physical conditions remain unchanged.
Mathematically it can be represented as,
Potential difference ∝ Current
V ∝ I
(When the value of V increases the value of I increases simultaneously)
V=IR
Where,
- V is Voltage in volts (V)
- R is Resistance in ohm (Ω)
- I is Current in Ampere (A)
Multiple and Submultiple Units
Units of Voltage
- Sometimes “E” is used instead of “V”
- E stands for Electromotive forces.
What is Electromotive force?
Electromotive force (e.m.f) is a measurement of energy that causes current to flow through a circuit. It can also be defined as the potential difference in charge between two points in a circuit. Electromotive force is also known as voltage, and it is measured in volts. The basic unit of voltage is the volt (V).
- Multiple units of voltage are:
- kilovolt (kV) 1 thousand volts or 10^3 V
- megavolt (MV) 1 million volts or 10^6 V
- Submultiple units of voltage are:
- millivolt (mV) 1-thousandth of a volt or 10^-3 V
- microvolt (µV) 1-millionth of a volt or 10^-6 V
How does Ohm’s Law work?
Ohm’s Law describes the current flow through a resistance when different electric potentials (voltage) are applied at each end of the resistance. Since we can’t see electrons, a model or an analogy of electrical circuits is used to help us understand circuits better like the water-pipe analogy. Water flowing through pipes is a good mechanical system that is analogous to an electrical circuit.
Here, the voltage is analogous to water pressure, the current is the amount of water flowing through the pipe, and the resistance is the size of the pipe. More water will flow through the pipe (current) when more pressure is applied (voltage) and the bigger the pipe, (lower the resistance).
Different Applications of Ohm’s Law
The main applications of Ohm’s law are:
- To determine the voltage, resistance or current of an electrical circuit.
- Ohm’s law is used to maintain the desired voltage drop across the electronic components.
- Ohm’s law is also used in dc ammeter and other dc shunts to divert the current.
Analyzing Simple Circuits Using Ohm’s Law
Resistive Circuits are analyzed using Ohm’s Law. The law is often used to find the voltage, current or resistance of the circuit. The law relates these three quantities by the equation V = IR. Ohm’s Law Triangle helps us remember this equation while solving problems. Here, the three quantities V, I and R are superimposed into a triangle with the voltage at the top and current and resistance below. The magic V I R triangle can be used to calculate all formulations of Ohm’s law.
OHM’S LAW TRIANGLE
If the value of voltage needs to be calculated and the values of the current and resistance are given, then to calculate voltage simply cover V at the top. So, we are left with the I and R or I X R. So, the equation for Voltage is Current multiplied by Resistance. Examples of how the magic triangle is employed to determine the voltage using Ohm’s law is given below.
Solving Problems Using Ohm’s Law Triangle
Example 1: If the resistance of an electric iron is 50Ω and 3.2A current flows through the resistance. Find the voltage between two points.
Ans.
If the value of Resistance is asked and the values of the current and voltage are given, then to calculate resistance simply cover the R. Now, we are left with the V at the top and I to the bottom left or V ÷ I.
Given, Resistance (R) = 50Ω
Current (I) = 3.2A
Therefore,
Voltage (V) = I X R
Voltage (V) = 3.2A x 50Ω
Voltage (V) =160V
Limitations of Ohm’s Law
Following are the limitations of Ohm’s law:
- Ohm’s law is not applicable for unilateral electrical elements like diodes and transistors as they allow the current to flow through in one direction only.
- For non-linear electrical elements with parameters like capacitance, resistance etc the voltage and current won’t be constant with respect to time making it difficult to use Ohm’s law.