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Ohm's Law Definition, Statement, Formula, Importance and Analogies Types

Ohm's law typically states that the current-carrying conductor between the two points is directly proportional to the voltage between those two points. The mentioned current between those two points is inversely proportional to the resistance of the conductor.

The basic equation in Ohms Law which proves this law is: V=IR, where:

  • V stands for voltage
  • I stands for current
  • R stands for resistance

However, this equation is only valid if the resistance is constant. Thus, the materials which obey Ohm’s law are called ohmic materials, and the materials which do not obey Ohm's law are called non-ohmic materials.

Limitation of Ohm’s Law

There are certain limitations of Ohm’s law which are stated below:

  • Ohm's law is not applicable in circuits that allow the current to flow in just one direction. Such circuits are known to be unilateral networks. Examples of such circuits are diodes, transistors, etc.
  • For Ohm's law to be applicable, the current-carrying in the conductor needs to be directly proportional at all times to the voltage between the two points. This also implies the resistance to be constant of the circuit.
  • A certain voltage has its own current flowing in the same direction. Now, if the direction of the voltage is reserved, it will still have a fixed magnitude, but no similar current as the earlier one will be generated.

The Importance of Ohm’s Law

This law is greatly used in physics, especially in the electrical and electronics branch. For example, it explains certain charge flows and circuit behaviour. Therefore, Ohm's law has great importance; few reasons are listed below:

  • This law allows you to control the amount of current flowing in the circuit by altering the number of resistors. More resistors result in a lesser flow of current.
  • It also helps you estimate your circuit's power using the formula P=VI, where P stands for electrical power. This power tells you the rate of energy flow per second. This helps you to ensure that your circuit provides enough energy.
  • You can use Ohm’s law along with Kirchhoff’s voltage law to calculate the voltage drop across any component of the circuit.

(Note: According to Kirchhoff’s voltage law, the algebraic sum of all the voltages of any closed loop in a circuit is zero.)

The Applications of Ohm's Law

There are many applications of Ohm's law that are used in our daily lives:

  • The fans' regulator that helps us change the fan’s speed works on Ohm’s law. The speed is adjusted by controlling the resistance with the help of the regulator. The power is also altered depending upon the desired energy needed.
  • The electric heater has a metal coil of high resistance, which allows a particular amount of current to pass through them and produces heat. Ohm's law is used here as it also helps determine the power that needs to be given to the electric heater.
  • Electric kettles and irons also use Ohm's law as it helps produce the required amount of heat by altering the excess flow of current with the help of resistors. In addition, this law helps add the required number of resistors and the suitable size of these resistors, which will be needed to restrict excess current and heat.
  • DC ammeters and other DC motors use Ohm’s law for producing appropriate current in the circuit. This is done by using the concept of the shunt, which is based on this law.

Types of analogies

Understanding the working of circuits that are based on Ohm's law can sometimes be confusing. To understand it well, there are mainly two types of analogies:

  1. Hydraulic analogy- In this analogy, the water pressure between two points in a horizontal pipe is the analogue for voltage. The rate of flow of the water is an analogue for the current passing. The disturbance to the flow of the water is the analogue for the resistance caused by the resistors.
  2. Temperature analogy- Similarly, in this analogy, the temperature gradient is the analogue for voltage. The flow of heat in the atmosphere is the analogue for the flow of current. The disturbances to the flow of heat is the analogue for the resistance caused by the resistors.

Ohm's law has proven many unsolved theories in the field of physics. This law provides a firm connection and relation between the circuit's voltage, current, and resistance.

Ohm's Law and its applications are extensively discussed in Class 10 Science Chapter 12 Electricity. 

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