Understanding Ohm’s law – Definition, Triangle , Calculation and its Applications

This article examines Ohm’s Law, a fundamental principle in electrical engineering that describes the linear relationship between the electric current flowing through a conductor and the voltage applied across it, assuming constant temperature and material properties.

Who discovered:

Ohmʼs Law was discovered by German physicist Georg Simon Ohm in 1827. He published his findings in a treatise titled ‘The Galvanic Circuit Investigated Mathematicallyʼ (Die galvanische Kette, mathematisch bearbeitet).

Definition of Ohms Law

Under constant ambient conditions, the electric current flowing in a circuit is directly proportional to the applied voltage and inversely proportional to the resistance of the circuit.

Circuit diagram and setup for Ohms Law verification

As illustrated in the diagram above, a simple circuit setup is used to analyze the relationship between current and voltage. An adjustable voltage source, denoted as ‘Vsʼ, is connected to create a potential diference at the inputterminals. A variable resistive load, represented as ‘R_Lʼ (in ohms), is connectedacross the voltage source. A control switch ‘Sʼ

To measure electrical parameters, a voltmeter is connected in parallel with the voltage source, while an ammeter is connected in series with the load to measure current. When the switch ‘Sʼ is turned ON, the circuit becomes closed,allowing the potential diference to drive the movement of electrons. As a result, current begins to flow through the circuit. The rate of electron flow (i.e.,current) depends on both the magnitude of the applied voltage and the resistance present in the circuit.

Acceleration of electrons from negative terminal to positive terminal is depending upon strength of potential diference and resistance of circuit

Methods and Verification ofOhm’s Law

With reference to above circuit diagram, verification of ohmʼs law as follows

Step-1

At initial condition, Voltage source, Resistance are at following position

• Voltage Source (Vs ) = At zero position. Hence Zero potential appears across its terminal Load Resistance
• Load Resistance (R_L ) = At Maximum position. Almost operates with infinity value resistance
• Switch(S) = OFF position. So circuit is in open condition

Step-2

• Switch (S) is closed. But Position of voltage source and load resistance are remains unchanged. But it makes closed circuit. So current can be circulated by applying voltage.
• Both Ammeter and voltmeter will show zero magnitude , because applied votage is zero.

Step-3

• As start to increase source voltage, potential diference develops across circuit, So electric current flowing through it.
• The voltmeter will show potential diference and ammeter shows current incircuit
• This rate of electric current flow depends on resistance connected across circuit as well as source voltage.
• This rate of electric current flow depends on resistance connected across circuit as well as source voltage.
• As long as increase input voltage, current starts to increase.
• As same as when load resistance adjusted current also varies. If load resistance adjusted from maximum to minimum current increases and viceversa.

Formulae and expressions

The following formula express the relation between voltage, current and resistance

I α V

I α 1/R

By combining both of above terms

I α V/R

Applying constant K, which is generally known as atmospheric condition andother external factors,

I K V/R

Let is consider K 1, So

I V/R

Here,

I Current flowing through circuits in Ampere A

V Voltage applied in circuit in volts V

R Load resistance connected in Ohms (Ω)

It is very interesting that, magnitude of any parameter can be obtained, if magnitude of other two parameters are available, to explain in more precise,With help of above equation

Voltage applied in circuit V = I x R

Resistance of circuit R = V/I

Current flowing in circuit I V/R

This Ohm’s law Triangle will help to understanding about Ohms law

Observation Table

Calculation using Ohm’s Law

A electrical circuit contains 24 Ohm load resistance, which is connected with abattery provides 12 volt output through a switch. Calculate load current i) When load resistance halved ii) when supply voltage doubled iii) When both are remains unchanged

Given:

Load Resistance R = 24 Ohm

Supply voltage V = 12 Volts

To find:

i) When load resistance halved

ii) When supply voltage doubled

iii) When both are remains unchanged

Solution:

Condition:1- When load resistance halved

Actual load resistance R = 24 Ohm

When it halved R x 1/2 = 12 Ohm

The current flowing through circuit I = V/R

I 12 / 12

I=1 Ampere

Condition: 2 When supply voltage is doubled

Actual supply voltage connected in circuit = 12 Volts

When it doubled V x 2=12 x 2= 24 volts

Then current flowing though circuit I V/R

I=24/24

I=1 Ampere

Condition:3 When Both are remains unchanged

Supply voltage V = 12 Volts

Load Resistance R = 24 Ohms

Then current flowing through circuit I V/R

I= 12/24

I= 0.5 Ampere

Result:

As examining above both conditions it has proved that , as per ohmʼs law the current flowing though circuit is proportional to the apply voltage and inversely proportional to the resistance.

Limitations of Ohm’s Law

1. Ohm’s law is applicable only for bilateral circuit element such resistors works in DC supply.
2. Unilateral element like diodes, transistors are not obeys with ohm’s law. Because they are conducting current in one direction only. Inductors, capacitors are having non-linear characteristics. Those current conduction as well as voltage across components are vary with respect to time.
3. Voltage in Non-metallic conductors such carbon rods are not obeying ohmʼs law

Applications

1. In School and university laboratories ,during conduction of experiments, rheostats are used to control in linear manner
2. In House hold appliances like ceiling fans , resistors are connected with series of with it. So it can be operated as speed control device
3. In decorative light applications, higher value fixed, are variable resistors are used control current across lower resistance circuit.
4. In industrial area, Pure Resistive devices like load banks are used to charging and discharging batteries