Lenz’s Law: Definition, Formulas, Problems and Discussion, and Definition of Electromagnetic Induction

Lenz Law – Sinaumed’s must have known that in everyday life, the presence of magnets is very much needed, especially in the use of technology? Yep, magnets are always a complement to the latest technology, one of which is the refrigerator. The refrigerator, aka the freezer, also uses magnets, you know , especially on the door. That’s why the refrigerator door always looks like someone is pulling it from the inside. Well, the use of magnets on the refrigerator door is the application of the process of electromagnetic induction which is closely related to Physics.

Physics is not just counting coconuts falling or how fast car tires go, but also about magnetic induction. In the case of electromagnetic induction this will definitely relate to Lenz’s law. Then what is Lenz ‘s Law? What is the formula for Lenz’s Law? What is the definition of electromagnetic induction? So, so that Sinaumed’s understands these things, let’s look at the following review!

How Does Lenz’s Law Sound?

Basically, Lenz’s Law is one of the laws in physics that provides a statement about Induction Electromotive Force (EMF). Yep, Lenz’s Law provides an explanation to all of us about how the direction of the induced current that occurs due to the Induction Electromotive Force (EMF) is. Lenz’s law is usually used in dynamic electric machines in generators and motors. Lenz’s law, coined by a physicist named Friedrich Lenz in 1834, states that:

“If an induced Electromotive Force (EMF) arises in a circuit, then the direction of the induced current generated is such that it creates an induced magnetic field that opposes the changing magnetic field (the induced current tries to maintain a constant total magnetic flux)”

In order to better understand Lenz’s Law, consider the following picture! The figure shows the direction of the induced current based on Lenz’s law in the form of a) a magnet approaching the coil; and b) the magnet moves away from the coil.

So, when the position of the magnet and the coil is stationary, then of course there is no change in the magnetic flux in the coil. It should be noted that flux in the field of physics has a definition in the form of ‘the amount of quantity (mass or heat) flowing through a certain area perpendicular to the flow per unit time’. Thus, the coil will appear magnetic flux and challenge the addition of magnetic flux that has penetrated the coil.

Therefore, the direction of the induced flux must be opposite to the magnetic flux, so that the total flux covered by the coil will always be constant. Likewise, when the magnet is removed from the coil, there will be a reduction in the magnetic flux in the coil itself. As a result, there will be an induced flux in the coil that opposes the reduction of the magnetic flux, so that the flux will always have a constant total. The direction of the induced current can also be determined by the right-hand rule, that is, if the direction of the thumb represents the direction of magnetic induction, then the direction of the fold of the other fingers will indicate the direction of the current.

Look again at the following picture!

The figure shows that if the magnet is moved closer to the coil, an induced electromotive force (EMF) will appear in the coil which causes an induced current to appear in the coil itself. As a result, there is also a magnetic field that opposes the fixed magnetic field, so that the direction of the current in the coil is from B to A, as is the case with the statement in Lenz’s Law.

Now, to better understand how the working principle of Lenz’s law requires two different methods, namely resistance to the motion of the poles and resistance to changes in flux. Just a little trivia , Sinaumed’s , in the previous description, we always mentioned magnetic flux. Indeed, what is magnetic flux? The existence of this magnetic flux is related to the number of magnetic field lines passing through a known area. The magnetic field remains perpendicular to the area bounded by simple circuits, especially those made of coils of wire.

Lenz’s law formula

As with other physical laws, even though they are related to magnetic induction, of course they have their own formula, namely:

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Examples of Questions and Discussion of Lenz’s Law

Example Question 1

  1. There is a magnetic flux enclosed by a coil, reduced from 0.5 Wb to 0.1 Wb in just 5 seconds. The coil consists of 200 turns of wire with a resistance of 4 Ω. Then, how strong is the electric current flowing through the coil?


Is known:

Φ1 = 0,5 Wb

Φ2 = 0,1 Wb

N = 200 turns

R = 4Ω

Δt = 5 seconds

Asked: I … ?


Induction Electromotive Force (EMF) is calculated using the equation:

the sign (-) indicates a reaction to a change in flux, namely the induced flux is in the opposite direction to the main magnetic flux. So that it will produce a current flowing through the coil in the form of I = ε/R = 16/4 = 4 A.

So, the electric current flowing through the coil is 4 A.

What Is Electromagnetic Induction?

Basically, the existence of Lenz’s Law is indeed related to the process of electromagnetic induction. What is electromagnetic induction anyway?

The term “electric” actually comes from the word “electron”, which in Greek becomes “amber”. The term “magnetic” also comes from magnesia, the name of the district in Greece where magnetism was first discovered. Well, electromagnetism is the name given to the combined science of electricity and magnetism. So it can be concluded that electromagnetic induction discusses two ways in which electricity and magnetism will be related to each other, in the form of:

  1. Electric current produces a magnetic field
  2. The magnetic field exerts a force on moving electric currents or electric charges (Giancoli, 2014)

The concept of electromagnetic induction was discovered by Joseph Henry, an American scientist who was then continued by Michael Faraday, a British scientist. Faraday then published the results of his research using experiments in the form of galvanometers, coils, and magnets. Look at the pictures of experiments conducted by Michael Faraday to examine the existence of this electromagnetic induction.

When the magnet is moved toward or away from the coil, the needle on the galvanometer will move to the right or to the left. Meanwhile, when the magnet is not moved, the needle on the galvanometer will not deviate to the right or left. For this, Faraday concluded that a constant magnetic field would not be able to produce a current, but a changing magnetic field could produce an electric current. Well, that electric current is called an induced current.

Based on these experiments, it was also shown that the movement of the magnet in the coil causes the galvanometer needle to deviate. It is the deviation of the galvanometer needle that shows that there is indeed an electric current at the end of the coil. The occurrence of an electric current is known as electromagnetic induction. Meanwhile, the potential difference that appears at the end of the coil is called the induced Electromotive Force (EMF).

Well, look again at the following picture!

The figure shows how induction of Electromotive Force (EMF) can occur. If the magnetic poles are brought closer to the coil, then the number of lines of force that enter the coil will also increase. It is the change in the number of lines of force that causes the deviation of the galvanometer needle. The same thing will happen if the magnet is moved out of the coil. However, the direction of the deflection of the galvanometer needle will be opposite to the original deflection. Thus, it can be concluded that the cause of the appearance of an induced Electromotive Force (EMF) is a change in the magnetic force lines enclosed by the coil.

Just a little additional information, Sinaumed’s, a device that can convert a type of energy (both chemical, mechanical and light energy) into electrical energy is called a source of electromotive force or often abbreviated as EMF. Examples of sources of this electromotive force are batteries, accumulators (accumulators), and generators. Batteries and accumulators can convert chemical energy into electrical energy, while generators can convert mechanical energy into electrical energy. Now, when current is drawn from the battery or accumulator, the voltage between the ends of the terminals drops below the value ɛ.

When compared to ordinary magnets, electromagnets do have many advantages, so they are often used in the latest technology to help humans do their daily work. Some of the advantages of electromagnets are as follows:

  • The magnetism can be varied, from the smallest to the largest size. The trick is to change one or all three of the electric current strength, the number of turns, and the size of the iron core.
  • Its magnetic properties are easy to appear and remove. The trick is to disconnect and connect the electric current using a switch.
  • It can be made into various shapes and sizes according to the desired needs.
  • The position of the poles can be changed. The trick is to change the direction of the electric current.
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Meanwhile, the strength of the electromagnet can increase if it experiences three things, namely: a) The current through the coil increases; b) The number of windings is increased; and c) Enlargement or lengthening of the iron core.


Get to know Faraday’s Law

The existence of Faraday’s Law turns out to be related to Lenz’s Law, you know, because both predict electromagnetic induction and induced Electromotive Force (EMF). Even the figure who discovered electromagnetic induction also contributed to Faraday’s Law, namely Michael Faraday, a British chemist and physicist. Even Michael Faraday also earned the nickname “Father of Electricity” because of his research related to electricity and became the forerunner of today’s great technology.

Michael Faraday was born on September 22, 1791 and died on August 25, 1867. He has studied various fields of science, including electromagnetic and electrochemical fields. Among scientists, the figure of Faraday is known as an early pioneer in research on electricity and magnetism so that his services are always remembered as the greatest scientist of all time.

In Faraday’s Law I, states that “The mass of the substance produced at the electrodes of fellow electrolyzers will be directly proportional to the amount of electric charge flowing”. That is, the mass of product (W) that has been deposited on the electrode will increase, along with the increase in the electric charge (Q) used.

According to Faraday, the magnitude of the induced Electromotive Force (EMF) at both ends of the coil will later be proportional to the rate of change in the magnetic flux, especially that which is enclosed by the coil. That is, the faster the change in magnetic flux occurs, the greater the induced Electromotive Force (EMF) that arises. Meanwhile, the meaning of magnetic flux is the number of lines of magnetic force that have penetrated a field. The magnitude of the change in magnetic flux can be calculated using the formula:

ΦB = B┴ A = BA cos θ


ΦB = magnitude of change in magnetic flux (Weber or T.m2 )

B┴ = magnetic field component perpendicular to the surface of the coil (Tesla)

A = surface area of ​​the plane (meter2)

θ = angle between B and a line perpendicular to the surface of the coil

Induction EMF Relationship with Faraday’s Law

Basically, Electromotive Force (EMF) is the work done per unit charge to produce an induced current. The induced current is the current generated in a wire loop. Faraday realized that electromotive force (EMF) and current could be induced in a loop and proved it through his second experiment, by varying the amount of magnetic field through the loop. The number of field lines that have passed through the loop does not actually affect the values ​​of the Electromotive Force (EMF) and the induced current.

Thus, when the north pole of the magnet is moved closer to the loop, the number of field lines passing through the loop will also increase. This increase causes the conduction electrons in the loop to move (as an induced current) and provide energy (as an induced emf). So, when the magnet stops moving, the number of field lines through the loop also no longer changes so that the induced current and induced emf disappear.

Through this Faraday’s Law, it will also explain the experiments that have been carried out by Michael Faraday from the negative sign on the rate of change with respect to time and the magnetic flux which has passed through the surface Φn, the same as when the Electromotive Force (EMF) around a closed loop and limited by surface. The negative sign determines the direction of the induced Electromotive Force (EMF).