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Difference Between EMF and Voltage

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  • Last Updated : 20 Jun, 2022

To understand the difference between EMF and voltage, we must first understand that EMF stands for electromotive force and refers to the voltage present at the source’s ends when no current is present. When we close the circuit to allow the electric current to flow, voltage is present at the source’s ends.

 

What is EMF?

EMF is made up of electrically charged particles that form when electrons are separated from atoms by consuming energy in the form of chemical, mechanical, or light. The electric potential generated by an electrochemical cell or by changing the magnetic field is known as electromotive force. S.I unit of EMF is volt. It is denoted by E.

Formula for EMF

E = V + Ir

Where, 

E is the electromotive force

V is the voltage

I is the current 

r is the  internal resistance

What is Voltage?

The difference between the electrical states on the poles is known as voltage. Electrons migrate from the negative to the positive half of a closed electrical circuit. The work done by the electric force in transporting the charge from one point of the field to another is referred to as electrical voltage. S.I unit of voltage is volt. it is represented by V. 

Formula for Voltage

V = IR

Where,

V is the voltage

I is the current

R is the resistance

Difference Between EMF and Voltage

 

EMF

Voltage

1. It refers to the voltage generated within the electric source. It’s the difference between two points’ potential differences.
2. External forces are used to move a charge from one pole to the next within a source. It is the process of transferring a charge from one pole to another via a wire.
3. Formula for EMF is E=V+ Ir Formula for voltage is V=IR
4. EMF meter is used to measure it. A voltmeter is used to measure it.
5. EMF is greater than voltage. It will always be less than EMF.
6. The dimension of EMF is M1L2T-3I-1 The dimension of Voltage is ML2T-3I-1

Sample Problems

Problem 1: Assume we have a circuit with a 3.2 V potential differential and a current of 0.6 A. At 0.5 ohms, the battery’s internal resistance. Make use of the EMF formula.

Solution:

Given,

  • V = 3.2 V
  • I = 0.6 A
  • r = 0.5 ohms

Using Formula:

E = V +Ir

   = 3.2+ 0.6×0.5

   = 3.5V

So, the EMF of the circuit is 3.5V.

Problem 2: Consider a circuit with a 5V potential difference, a current of 0.9A, and a battery internal resistance of 0.7ohms. Calculate the battery’s EMF.

Solution:

Given,

  • V= 5 V
  • I = 0.9 A
  • r = 0.7 ohms

Using Formula:

E = V+ Ir

   = 5+0.9×0.7

   = 5.63V

So, The EMF of the circuit is 5.63V.

Problem 3: If the battery’s terminals are connected, calculate the current that will flow inside the battery at a voltage of 5 volts and an internal resistance of 0.02 ohms.

Solution:

Given,

  • V = 2 V
  • r = 0.02 ohms

V= IR

Substituting values in the equation

I= V/R

 = 5/0.02

 = 250 

So, the current is 250 A.

Problem 4: If the terminals of a 10 Volt battery with 2 ohm internal resistances are linked, calculate the current that will flow inside the battery.

Solution:

Given,

  • V = 10 V
  • r = 2 ohms

V  = IR

Substituting the values in the equation

I = V/R

  = 10/2

  = 5 

So, the current is 5 A

Problem 5: If the battery’s terminals are connected, calculate the current that will flow inside the battery at a voltage of 20 volts and an internal resistance of 5 ohms. Determine the battery’s terminal voltage.

Solution:

Given,

  • V = 20 V
  • R = 5 ohms

V = IR

Substituting the values in the equation

I = V/R

   = 20/5

   = 4

So, the current is 4 A

Using the EMF formula for terminal voltage

E = V+Ir

Substituting the values the equation

V = E – Ir

    = 20 – 4×5

     = 20 – 20

     = 0

So, the terminal voltage is 0 V

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