Electromotive Force

Dhristi JEE 2022-24

Introduction - What is Electromotive Force?

Electromotive Force is the amount of energy delivered per unit electric charge by a power source such as a generator or a battery (abbreviated E or EMF). As the generator or battery works on the electric charge being transported within itself, energy is changed from one form to another. The device's positive terminal becomes positively charged, while the negative terminal becomes negatively charged. The Electromotive Force is the work done on a unit of electric charge, or the energy gained per unit of electric charge. It is abbreviated E in the international metric system, but it is also known as EMF.


Electromotive Force has force in its name but technically it is not a force. It is generally measured in volts, which is equal to one joule per coulomb of electric charge in the meter–kilogram–second system. In the centimeter–gram–second system, the statvolt, or one erg per electrostatic unit of charge, is the electrostatic unit of Electromotive Force.

 

Electromotive Force, measured in volts, is the electrical activity produced by a non-electrical source in electromagnetism and electronics. Devices, such as batteries (which convert chemical energy) or generators, create an Electromotive Force by converting various sources of energy into electrical energy (which convert mechanical energy). Electromotive Force is sometimes described using a water pressure analogy. (In this example, "force" does not refer to forces of interaction between bodies.)

 

The electromagnetic work that would be done on an electric charge (an electron in this case) if it traveled once around a closed loop of a conductor is described as EMF in electromagnetic induction. The electric potential's scalar field is not specified for a time-varying magnetic flux joining a loop due to a circulating electric vector field, but an EMF accomplishes work that is abbreviated E in the international metric system, but it is also known as EMF.

 

Overview

The Electromotive Force is abbreviated as EMF. The Electromotive Force is the voltage at the terminals of the source in the absence of an electric current. The concept of Electromotive Force refers to the amount of work required to separate the charge carriers in the source current, such that the force acting on the charges at the terminals of the source is not a direct consequence of the field. EMF is developed as a result of internal resistance.

 

What is meant by Electromotive Force? The Electromotive Force (EMF) is defined as- The amount of work done in the energy transformation (or conversion) and the amount of electricity that passes through the electrical source or the generator. The Electromotive Force (EMF) is measured in Volts and denoted by the symbol ε (or E). In this article, we will discuss mainly what is Electromotive Force, what is EMF in Physics, etc.

 

What is EMF in Physics?

Now we will understand what EMF is in Physics and what is meant by EMF in Physics. So, the Electromotive Force is the maximum potential difference between two electrodes of the cell when no current is drawn from the cell. The Electromotive Force is denoted by E or sometimes it is also denoted by the symbol ε.

 

We know that the charges move in the electric circuit, for the motion of the charges in a given electric circuit we need to apply an external force to it. We say that the battery or an external electric source such as a battery applies such force which will give acceleration to the charges and it is known as the Electromotive Force. Despite its name, it’s not a form of force but a potential difference.

 

If the Electromotive Force is not a form of force at all, then why is it termed as the Electromotive Force, what are EMF and potential difference, and what is the source of EMF? To answer these doubts, consider a simple circuit of a lamp connected to a battery, as shown in the Figure below.

 

(Image will be updated soon)

 

The battery (any electro-voltaic cell) can be represented as a two-terminal device that keeps one terminal at a higher potential than the second terminal. The higher electric potential is sometimes known as the positive terminal and it is generally labeled with a plus sign. The lower-potential terminal is known as the negative terminal and is labeled with a minus sign. This is known as the source of the EMF.

 

When the source of the Electromotive Force is disconnected from the lamp, there is no net flow of charges within the EMF source. Once the battery is reconnected to the lamp, charges will flow from one terminal of the battery, through the lamp (causing the lamp to glow), and back to the other terminal of the battery. If we consider positive current flow which is also known as the conventional current flow, positive charges leave the positive terminal, travel through the lamp, and enter the negative terminal of the EMF source. This is how an EMF source is configured. Now, what is the Electromotive Force of a cell? The Electromotive Force of a cell is the potential difference developed at both ends of the given battery.

 

What is the Unit of Electromotive Force?

What is the Electromotive Force measured in? Let us have a look at what is the unit of Electromotive Force, the formula for Electromotive Force is given by,

 

⇒ ε = V + Ir

 

Where,

V- The applied potential difference.

I- The current flowing through the circuit.

r- The internal resistance of the circuit.

 

Therefore, the unit of Electromotive Force is in volts. The Electromotive Force (EMF) is expressed as the number of Joules of energy supplied by the source divided by each Coulomb to enable a unit of electric charge to move across the circuit. Mathematically it is given by:

 

⇒ ε = Joules/Coulomb

 

Therefore the dimensions of the Electromotive Force M1L2T-3I-1.The answer to the question what is the si unit of Electromotive Force, from the expression of EMF we can say it is Joules/coulomb.

 

Example:

Consider an electrical circuit with a potential difference of 7V, a current of 1A, and the internal resistance of the battery is 0.7ohms. Calculate the EMF of the battery.

Given,

 

Potential difference = V = 7V

Current in the circuit = I = 1A

Internal resistance of the battery = r = 0.7Ω

 

Now, EMF of the circuit is given by:

 

⇒ E = I(R + r)

 

Where,

R - External resistance of the electrical circuit.

r - Internal resistance of the given circuit.

I - Current flowing through the circuit.

 

On rearranging the above expression,

 

⇒ E = IR + Ir

 

We know that the product of current in the circuit and the external resistance is the potential difference across the resistance. Thus,

 

⇒ E = V + Ir

 

Substituting given values in the equation,

 

⇒ E = 7 + (1 × 0.7) = 7.7 volts

 

Therefore, the EMF of the battery is given by 7.7V.

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FAQs (Frequently Asked Questions)

1. What is Meant by the EMF of a Battery and What is EMF and Voltage?

Electromotive Force is defined as the amount of work done in the energy transformation (or conversion) and the amount of electricity that passes through the electrical source or the generator. The Electromotive Force (EMF) is measured in Volts. The voltage of the source is different from that of the EMF of the source. Voltage is the potential difference developed between the two electrode potentials of a battery under any conditions.

2. What is the Measure of Electromotive Force?

The Electromotive Force is measured in volts, denoted by V.

3. What is the relationship between Faraday's law and Electromotive Force?

According to Faraday's law, every change in the magnetic field of a coil will cause an EMF in the coil (and hence also a current). It is proportional to the rate of change in magnetic flux () minus the rate of change in magnetic flux (). (Note that N is the coil's number of turns.)


Transformers, which are used in the transmission of energy in the UK national grid and are now a must in our houses, have helped society, thanks to Faraday's law. It's also used in electric generators and motors, such as those found in hydroelectric dams, which provide the electricity that's become so important to our modern technology needs. MAG-DRIVE, a current Birmingham research project, is looking for ways to develop and improve permanent magnet materials for use in the future generation of electric vehicles. EMF is also produced by solar cells, making it a vital component of renewable energy research.

4. What is (EMF) Electromotive Force?

The electric potential generated by an electrochemical cell or by changing the magnetic field is known as Electromotive Force. EMF is a common abbreviation for Electromotive Force.


A generator or a battery is used to transform energy from one form to another.One terminal becomes positively charged, while the other becomes negatively charged in these devices. As a result, work performed on a single unit of electric charge is referred to as Electromotive Force.


The electromagnetic flowmeter, which is based on Faraday's law, employs Electromotive Force.


Electromotive Force Symbol

The symbol for Electromotive Force is ‘ε’.

5. Can you explain the difference between Electromotive Force and potential difference?

The differences are-


Force Electromotive

  • EMF is the amount of work done on a single unit charge.

  • The EMF does not change.

  • The EMF is unaffected by circuit resistance.

  • Electric, magnetic, and gravitational fields are all caused by EMF.

  • E is the symbol for it.


Potential Distinction

  • The potential difference is the amount of energy dissipated when a unit charge travels through the components.

  • The difference in potential is not constant.

  • The resistance between the two sites during the measurement determines the potential difference.

  • The only electric field is induced due to the potential difference.

  • V is the symbol for it.

6. Can Electromotive Force be negative?

Yes, a negative Electromotive Force is possible. The negative sign indicates that the Electromotive Force is being created to counteract the cause. If the EMF is induced by a rising magnetic field in the -z direction, the EMF will be induced to produce an increasing magnetic field in the +z direction.


Consider an inductor that produces an EMF that is in direct opposition to the incoming power. The resulting EMF is thus interpreted as negative because the flow direction is opposite that of the true power. As a result, it is conceivable for the Electromotive Force to be negative.

7. What is the difference between Electromotive Force and terminal voltage?

When a circuit is turned on, the potential difference across the terminals of a load is called terminal voltage.


The largest potential difference that a cell or generator can deliver when no current flows through it is called E.m.f.


The terminal voltage is measured with a voltmeter.


The e.m.f. is measured with a potentiometer.


The EMF of the cell is never greater than the terminal voltage. It's due to the current going through the cell's or generator's internal resistance, which causes a drop in potential. The following equation connects the EMF (E) with the terminal (V).


E = V + Ir, where I is the current and r is the cell's internal resistance.

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