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Difference Between EMF and Voltage
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Current Electricity
EMF (electromotive force) and Voltage are very similar concepts in the field of electrostatics yet they have a distinctive difference. The electromotive force of a cell can be measured by the voltage across the cell. Hence, an electromotive force is a property of potential difference and voltage is a quantity to measure potential difference and this is the major difference between EMF and Voltage.
In this Physics article, you will learn about the concepts of EMF and voltage, the difference between EMF and voltage, its importance and wide applications.
What is an EMF (Electromotive Force)?
To understand the concept of EMF, we are going to use the electrolytic cell responsible for the electrolysis of an aqueous solution as a reference, as shown in the image below. An electrolytic cell is a simple device to maintain a steady electric current.
- A cell has two electrodes, a positive and a negative electrode and is immersed in an ionic solution.
- These electrodes exchange the electric charge with the electrolytes in such a way that the positive electrode has a potential difference of +V and the negative electrode has a potential difference of -V.
- When there is no current flowing through the cell, the potential difference is the same throughout, i.e, +V + V- = constant. This difference is called the electromotive force of the cell and is represented by
. - Thus,
EMF Formula
EMF can be calculated by the formula
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 potential difference between two charged points in a conductor is known as voltage.
- It is represented by the symbol V.
- It is the potential energy per unit charge.
- It is generally measured across a load or circuit, observed by Ohm’s law, where the potential difference in a circuit is directly proportional to the resistance and the current flowing across the circuit.
Voltage Formula
The formula for voltage is given by
V=IR
Where,
V= voltage
I = current
R= reisistance
Difference Between EMF and Voltage
Some key differences between EMF and voltage are listed below.
|
EMF |
Voltage |
|
EMF has a greater magnitude and constant intensity. |
Voltage has non-constant, lower strength than EMF. |
|
EMF is not influenced by circuit resistance. |
The resistance of the circuit affects voltage. |
|
EMF is a Coulomb force operation. |
Voltage is a Non-Coulomb force operation. |
|
EMF is the cause of Voltage. |
Voltage is the effect of EMF. |
|
EMF can be measured between the end terminals when there is no current flowing through them. It can be measured by an EMF meter. |
Voltage can be measured between any two points. It can be measured by Voltmeter. |
|
It is a quantitative measure to calculate the potential difference. |
It is the potential difference across two points in an electrode. |
|
It is represented by the symbol V. |
It is represented by |
|
A change in voltage would directly affect the current in the circuit. |
As the name suggests, EMF can affect the electric as well as magnetic fields. |
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Applications of EMF and Voltage
The following are the applications of EMF and Voltage
- EMF can be used to understand the concept of electrolysis and study various systems based on Faraday’s laws of electrolysis.
- EMF is useful to maintain a steady current flow in the circuit and potential differences across the circuit.
- Voltage is a quantitative measure and is used to measure the potential difference across loads and resistances of the circuit to control the flow or current.
Solved Examples on EMF and Voltage
Solved Example 1: A coil with 60 turns is wrapped around a square frame with an area 0.15 sq. m. The coil is immersed inside a magnetic field that changes at the rate of 0.01 T/s. What is the induced emf in the coil?
Solution 1:
Number of turns: 60
Area: 0.15 sq. m
Change in the magnetic field:
0.01 T/s
Solved Example 2: The magnetic flux associated with a coil changes from zero to 6 x
Solution 2:
Initial flux
Change in flux
By Faraday’s law of electromagnetism, the magnitude of induced e.m.f. is given by
Solved Example 3: Effective area of coil = nA = 4 sq. m, Angle between the plane of coil and the magnetic field = \({\theta} = 90^\circ\), Initial magnetic induction = \(B_1 = 0.05 \frac{Wb}{m^2}\), decrease in magnetic induction = 20%, Time in which change took place = dt = 10 s.
Solution 3:
Final magnetic induction = \(B_2 = B_1 – 20%\) of
\(∴ B_2 = 80% B_1 = 0.80 x 0.05 = 0.04 \frac{Wb}{m^2}\)
Initial flux
Final Flux
Change in flux
By the Faraday’s law of electromagnetism, the magnitude of induced e.m.f. is given by
Points to Remember
- When no current is flowing, electromotive force (EMF) equals the terminal potential differential. Despite the fact that both EMF and terminal potential difference (V) are expressed in volts, they are not the same entity.
- EMF is the quantity of energy (E) that the battery supplies to each coulomb of charge (Q) that passes through.
Hope this article was informative and helpful for your studies and exam preparations. Stay tuned to the Testbook app for more updates and topics related to Physics and various such subjects. Also, reach out to the test series available to examine your knowledge regarding related exams.
Difference Between Emf and Voltage FAQs
Are EMF and voltage equal?
EMF is the cause to generates a potential difference across the circuit whereas voltage is used to measure this potential difference.
How do I calculate emf?
EMF can be calculated by the following formula
What is the importance of emf?
EMF acts as a charge pump to move the charges across the conductor and create a potential difference in the circuit.
Does EMF increase with voltage?
Yes, the higher the EMF higher would be the voltage.
What is the difference between emf and terminal voltage?
In simple words, EMF is an open circuit voltage and is dependent on the internal resistance of the circuit, whereas terminal voltage is a closed circuit voltage.