Understanding Electromotive force and its units

In this article, we will introduce electromotive force from electromagnetic Induction. In electromotive force, electric actions whose production take place by the non-electrical source.

Here we will discuss  electromotive force, motional electromotive force and the dimension of electromotive force.

This article will also help you to understand the basics of  electromotive force, the Electromotive force formula and its SI unit. Electromagnetic induction is an important chapter in class 12 Physics and Motional Electromotive Force is an important topic that falls under the chapter.

Electromotive force

Electromotive force is the terminal potential difference of a battery (or another energy source) when there is no electrical current flow. The electric potential generated by either changing the magnetic field or by an electrochemical cell is called electromotive force. ε Is the symbol that has been accepted by experts for the electromotive force. The use of a generator or battery takes place for converting energy from one form to another form.

Electromotive Force represents the electrical action whose output takes place by a non-electrical origin. While transducers refer to the tool that delivers an electromotive force by stimulating the conversion of other forms of energy into electrical energy like batteries or generator

Electromotive Force is the force that maintains a constant potential difference. Electromotive Force can also be specified as the full potential difference between the negative electrode and the positive electrode of a cell in an open circuit and can be generated by an electrochemical cell or by shifting the magnetic field.

Motional Electromotive force

An electromotive force that has been generated by the motion of the conductor across the magnetic field is called a motional electromotive force. The equation is provided by E= -LLB, where the – sign is correlated with Lenz’s Law. The equation is true considering length, velocity and field are perpendicular to each other.

Motion is one of the main reasons for induction. For example, a magnet that moves toward a coil generates an Electromotive force.

The formula for the Electromotive force

ε= Ir+IR is the formula for the Electromotive force.

  = Ir+V

Where,

• ε is the EMF(electromotive force)
• r is the internal resistance of the cell
• I am the current across the circuit
• R is the external resistance
• V is the voltage of the cell

Therefore, the unit of electromotive force in volts.

The Dimension of Electromotive Force

The electromotive force (EMF) is conveyed as the number of Joules of energy given recharged by the source split by each Coulomb to stimulate a unit electric charge to move across the circuit. Mathematically it is given by:

⇒ ε = Joules/Coulomb

The dimensions of the electromotive force in the MLT system are given as M1L2T-3I-1.

 Unit of the Electromotive Force

The unit for electromotive force is Volt.

from the expression of electromotive force, we can say that

The SI unit of electromotive force is = Joules/coulomb.

Factors that Affect the Induced Electromotive Force

Some factors can affect the induced Electromotive Force. They are as follows:

• The induced Electromotive Force is proportionate to the number of bends in a coil.
• The velocity at which the conductor runs through the magnetic field.
• The size of the conductor.
• The velocity at which the conductor reduces the magnetic lines of force.

 Difference between Electromotive force and Terminal Voltage

1. Electromotive force is the total voltage of a cell while the terminal voltage is the voltage at the terminals of a cell.
2. The value of terminal voltage is always less than the electromotive force.
3. One can interpret terminal voltage as the potential difference across a load’s terminals when the circuit is on. In disparity, an electromotive force is the absolute potential difference that a battery can transmit when there is no flow of electrical current.
4. A potentiometer is used for measuring the Electromotive force whereas a voltmeter is used for measuring the terminal voltage.
5. The voltage is interpreted by electric force or Coulomb force operation while electromotive force is interpreted by non-electric force or non-coulomb force operation.
6. Work performed by voltage will not be the ultimate work of the battery while work done by the electromotive force will be the ultimate work of the battery or cell.
7. Intensity will be fluctuating due to voltage dip across the outer friction while intensity will be constant in EMF.
8. Voltage is induced only in an electric field whereas electromotive force is induced in a magnetic field, electric fields or gravitational fields.
9. The voltage is evaluated by utilizing ohm’s law, given by: V = IR,where I is current flowing through the circuit and R is external resistance of the electrical circuit and the formula utilized to evaluate electromotive force is given by: ε = I(R+r) where R- external resistance of the electrical circuit and r is internal resistance of the given circuit.

Example: Let us assume a photovoltaic cell has an electromotive force of 20.0 V and internal resistance of 0.2 Ohms. The photovoltaic cell is connected with an electrical circuit having a load of 18 Ohms. Let us find out the terminal voltage in the electric circuit.

When the resistance is connected in series

R = R1 + R2

R1 = 0.2 Ohms,

R2 = 18  Ohms

Resultant resistance

R = 0.2 Ohms + 18 Ohms

   = 18.2 Ohms

Current in the circuit

I = EMF/(R)

I = 20/18.2

  = 1.098 A

Where I is current in the circuit

Terminal Voltage of the circuit

V = EMF-Ir

   = 20 – 1.098*0.2

   = 19.78 Volts

It can be seen from the result that Terminal voltage is less than the Electromagnetic force. 

Conclusion

Electromotive force or EMF of a cell is virtually an aspect of the cell (or energy source) that is eligible for running an electric charge around the circuit. Volts are the unit of the electromotive force. Certain factors affect induced EMF.