Faraday’s Law: Definition, Principles, and Example Problems

Faraday’s law – Faraday’s law is one of the laws of physics that has made a major contribution to the progress of electricity. This law makes electricity a very important thing for modern human life. Michael Faraday at that time succeeded in creating the first electric generator that was used to meet human needs until the discovery of electromagnetic induction.

It was explained that there were discoveries regarding the quantitative aspects contained in electrolysis and the results were in the form of Faraday’s two laws of electrolysis. Several types of quantitative aspects are mentioned, such as the mass of the product, the volume of the gas, the number of moles of electrons, the current strength, and the electrolysis time required in the process.

Faraday’s Law Inventor Biography

Portrait of Michael Faraday.

Faraday’s law was formulated by the British chemist and physicist, Michael Faraday. In 1833, Faraday described discoveries about the quantitative aspects of electrolysis that eventually led to Faraday’s two laws of electrolysis.

Quoted from the XII Chemistry Module compiled by Arni Wiyati (2020) in this case electrolysis is an electrochemical cell in which electrical energy is used to carry out non-spontaneous redox reactions. The quantitative aspects referred to in the electrolytic cell are the mass of the product, the volume of the product gas, the number of moles of electrons, the current strength, and the time of electrolysis. The two laws obtained are divided into Faraday’s laws 1 and 2.

Michael Faraday (22 September 1791-25 August 1867) himself was a British scientist who earned the nickname “the father of electricity”, because thanks to his efforts electricity became a technology that was of many uses. He studied various fields of science, including electromagnetism and electrochemistry. He also invented the device that would become the Bunsen burner, which was used in nearly all science laboratories as a practical source of heat.

The effects of magnetism led him to discover the ideas that became the basis for the theory of the magnetic field. He gave many lectures to popularize science to the general public. His rational approach in developing theory and analyzing results is admirable.


1. Michael Faraday’s Childhood

Michael Faraday was born in Newington Butts, London, United Kingdom. The family moved to London in the winter of 1790. And it was in the spring of that year that Faraday was born. Faraday was the third of four children who had little formal education. At the age of 14, he was apprenticed as a salesman and bookbinder. During his seven years working as a bookbinder and salesman gave him many opportunities to read many books and it was during this time that he developed his curiosity towards science.

At age 20, he quit his apprenticeship and attended lectures given by Humphry Davy. It was from there that he later got in touch with Davy and eventually became Davy’s assistant when the scientist experienced impaired vision due to nitrogen trichloride. And this is where he started his extraordinary life story.

2. Michael Faraday’s Scientific Achievements

a. Chemistry

Faraday began his work in chemistry as an assistant to Humphry Davy. He succeeded in discovering Chlorine and Carbon substances. He also succeeded in liquefying several gases, investigating alloys of steel, and manufacturing several new types of glass intended for optical purposes. Faraday was the first to invent the Bunsen Burner. Which is now widely used throughout the world.

Faraday worked extensively in chemistry. Find other chemical substances, namely Benzene and dilute chlorine gas. The liquefaction of chlorine gas aims to establish that the gas is a vapor of a liquid having a low boiling point and to provide a more certain basic concept of molecular assemblage.

He also determined the composition of the hydrated chlorine clathrate. Faraday was the discoverer of the Law of Electrolysis and popularized the terms anode, cathode, electrode and ion. He was also the first to study metal nanoparticles.

b. Electricity and Magnetism

Faraday became famous for his work on electricity and magnetism. His first experiment was to make a voltaic pile construction with 7 and a half pennies, stacked with 7 sheets of zinc and 6 sheets of salt water soaked paper. With this construction he managed to decompose magnesium sulfate.

In 1821, Hans Christian Ørsted published the phenomenon of electromagnetism. It was from here that Faraday then began research that aimed to create a device that could produce “electromagnetic rotation”. One of the tools he succeeded in creating was the homopolar motor.

In this tool there is a continuous circular motion caused by the force of the magnetic circle around the cable which is extended into a pool of mercury where a magnet has previously been placed in the pool, so the cable will rotate around the magnet when an electric current is supplied from the battery. This discovery became the basis of today’s electromagnetic technology.

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Faraday made a breakthrough when he wound two separate coils of wire and found that current is carried in the first coil, while the current is introduced in the second. This is what is known today as mutual induction. The results of this experiment resulted in that “a change in the magnetic field can produce an electric field” which was then made a mathematical model by James Clerk Maxwell and is known as Faraday’s Law.

vs. Diagmatism

In 1845, Faraday discovered that most matter exhibits a weak resistance to an electric field. This event is called diagmatism. Faraday also discovered that the plane of polarization of linearly polarized light could be rotated by the application of an external magnetic field in the direction of motion of the light. This is what is called the Faraday Effect.

Then in 1862, Faraday used a spectroscope to find differences in changes in light, changes of spectral lines by applying a magnetic field. However, the equipment he used at that time was inadequate, so it was not enough to determine the changes in the spectrum that occurred. This research was continued by Peter Zeeman and he published his results in 1897 and received the Nobel Prize for Physics in 1902 thanks to references from Faraday.


Faraday’s Law Working Principle

Before knowing more about Faraday’s Law and what are the applications in it. It is necessary to first understand the working principle of this law, starting from its understanding. Faraday’s law is a rule whose content is in the form of an explanation of the relationship between the mass of a substance present at an electrically charged electrode produced by an electrolytic supply.

Michael Faraday saw that each atom obtained was carried by one mole of electrons, this he observed during the process of electrolysis. As a result, a constant is found that is useful for calculating the amount of charge contained in one mole of electrons. Making it easier to calculate stoichiometry is one of the benefits.

There is the Faraday constant which is used to calculate the amount of charge contained in one mole of electrons. The Faraday constant facilitates the process of electrolysis stoichiometric calculations and in effect makes it possible to carry out stoichiometric calculations without having to take into account the electron charge at any time.

The Faraday constant is represented by F and has the following values, F is L/Mole x charge of the electron or electrons, F is (6.02214 x 10^23 electrons/mol) x (1.6022 x 10^-19 C/electron) and F is 96,500 C. After that the next understanding related to Faraday is the division of this law which is divided into two types.

Basically, Faraday’s law is used to make hypotheses or predictions regarding how a magnetic field can interact with an electric circuit. Useful to bring up the electromotive force or known as electromagnetic induction. Faraday’s law is divided into two types, namely Faraday’s law I and Faraday’s II.

1. Faraday’s Law I

Faraday’s law I states that the mass of a substance that is dissolved or precipitated is directly proportional to the charge passed through the cell and the equivalent mass of the substance. Faraday’s law I reads as follows, the mass of the substance obtained at the electrode during the electrolysis process is proportional to the amount of electric charge flowing.

From the sound of the law above it can be seen that the mass of the product which is symbolized by W, precipitated or dissolved on the electrode will be more and more. Increasing the number of masses goes hand in hand with an increase in the electric charge which is symbolized by the Q used, so it can be concluded that W = Q, the formula for Faraday’s law I is W = e. i . t/F.

  • W is the mass of the substance produced in terms of grams.
  • e is equivalent.
  • i is the current strength in amperes.
  • t is the time in seconds.
  • F is the Faraday constant, which is 96,500 Coulombs/mol.

2. Faraday’s Law II

Faraday II’s law has a very interesting point, where this law applies to two electrolytic cells with different substance properties. The existence of a different number of zets of electrolysis products so that they appear is directly proportional to the equivalent mass of the existing substances, in understanding this according to the sound of Faraday II’s law.

The sound of Faraday II’s law is that the mass of a substance produced in an electrode that appears during electrolysis (W) is directly proportional to the equivalent mass (e) of the substance. If some electrolytic cells are arranged in series or the same amount of electric current includes the same amount of electric charge.

So that it will bring up the mass ratio of the substances obtained to be the same as the equivalent mass ratio of each substance. The formula for Faraday II’s law is W1 / W2 = e1 / e3, W1 is the mass of substance 1 (grams), W2 is the mass of substance 2 (grams), ei is the equivalent of substance 1 and e2 is the equivalent of substance 2.

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This explanation confirms that the application of this law is used to account for the quantitative aspects of the substances involved in reactions in electrolytic cells. In addition, Faraday is also a law regarding electromagnetic induction after conducting an experiment on how a magnetic field induces an electric current.

Discovery of Electromagnetic Induction

Michael Faraday became head of the laboratory at the Royal Institute to replace Sir Humphry Davy who was seriously ill at that time. Six years later Faraday discovered electromagnetic induction by using an induction ring as the first electronic transformer in the world at that time.

In a second experiment, performed in September 1831, Faraday discovered electric-magnetic induction, which is the production of a steady electric current. This discovery later became the principle behind the birth of modern electric motors, transformers and electric generators. Likewise with the discovery of Faraday’s Law which has been explained in detail above.

Prior to 1839, Michael Faraday experienced a problem that made his health decline drastically, namely a nervous breakdown. The scientist’s deteriorating health reduced his research, although he still carried his responsibility as a lecturer at that time until 1861.

Right at the age of 75, the inventor of electricity finally died at his residence in Hampton Court. On August 25, 1867, according to reports Faraday died while sitting in his office. His body was later buried in Highgate Cemetery in North London and a monument was erected as a memorial.


Examples of Faraday’s Law Questions

1. Problem 1

The source of the electromotive force is…

a. magnet moving around the coil.
b. electric charge moving around the coil.
c. a stationary magnet around the coil.
d. two permanent magnets around the coil.
e. the interaction of the magnetic poles around the coil.

The electromotive force originates from a magnet that moves around the coil.

Answer: A

2. Problem 2

When Faraday conducted an experiment to prove whether a magnetic field could generate an electric current, a phenomenon occurred where an electric current appeared when a magnet was in a state of ….

a. move.
b. away from the coil.
c. shut up.
d. static.
e. close to the coil.

When Faraday conducted an experiment to prove whether a magnetic field could generate an electric current, a phenomenon occurred where an electric current appeared when the magnet was in motion.

Answer: A

3. Problem 3

The correct statement about the magnitude of the induced emf is…

a. proportional to the magnitude of the magnetic field.
b. Inversely proportional to the magnitude of the magnetic field.
c. Proportional to the change in magnetic flux and inversely proportional to the number of turns of the coil.
d. Inversely proportional to the change in magnetic flux and the number of turns of the coil.
e. Proportional to the change in magnetic flux and the number of turns of the coil.

The magnitude of the induced emf is proportional to the rate of change of the magnetic flux and the number of turns of the coil.

Answer: E

4. Problem 4

What is the equivalent mass for the following reaction Cu2+ (aq) + 2e – Cu (s) if it has, copper (Cu) Ar = 63.5 ?

Judging from the above reaction, it can be seen that there is a change in the oxidation number, namely at +2, so the equivalent mass of Cu is ME = Ar/bioxal = 63.5/2 = 31.75. If the same amount of electricity is supplied to two or more electrolytic cells with different electrolytes, the ratio of the substances released is directly proportional to the ratio of the equivalent masses of the substances.

5. Problem 5

If in the network above a Cu deposit of 5 grams is formed, then how much Ag is deposited on the electrode? (Cu = 63.5, Ag = 108).


To calculate the mass of Ag, wag uses the formula provided in the figure above where ME = Ar / oxidation state. While it is known that Cu, wcu = 5 grams. To calculate MEcu and MEag, you must first write down the Cu and Ag reduction reactions as shown below.

If the Faraday I and Faraday II laws are combined, we get w = I xtx ME, then this comparison becomes an equation by adding a factor of 1/96,500 and we get the formula for Faraday’s law w= 1/96,500 x I xtx ME.

6. Problem 6

A coil consists of 50 turns, the magnetic flux in the coil changes by 5 x 10 -3 Weber in 10ms (milliseconds) intervals. Calculate the Electromotive Force or induced emf in the coil!


Number of turns (N) = 50
Time interval (Δt) = 10ms = 10 x 10 -3 seconds
ΔΦ = 5 x 10 -3 weber
emf induction (ɛ ) = ???

Answer :

e = -N (ΔΦ/∆t)
e = -50 (5 x 10 -3 wb / 10 x 10 -3 )
e = -50 (0.5)
e = -25V

So, the Induction Electromotive Force is -25V .

Thus the explanation and discussion of the principles of Faraday’s law, starting from the meaning and examples of questions that are easy to work on. sinaumedia makes students love to understand science related to nature, including basic things such as the occurrence of electric currents and these laws in it.