ELITE TUTORING
LENZ’S LAW
Lenz’s law states that:
The induced electromotive force with different polarities induces a current whose
magnetic field opposes the change in magnetic flux through the loop in order to ensure
that original flux is maintained through the loop when current flows in it.
Named after Emil Lenz, Lenz’s law depends on the principle of conservation of energy
and Newton’s third law. It is the most convenient method to determine the direction of
the induced current. It states that the direction of an induced current is always such as
to oppose the change in the circuit or the magnetic field that produces it.
The Lenz’s Law is reflected in the formula of Faraday’s law. The negative sign is
contributed from Lenz’s law. The expression is:
△ϕ
𝑒𝑚𝑓 = −𝑁 ( )
△𝑡
Where,
Emf is the induced voltage (also known as electromotive force).
N is the number of loops.
Δϕ Change in magnetic flux.
Δt Change in time.
Lenz’s Law Experiment
To find the direction of the induced electromotive force and current we look to Lenz’s
law. Some experiments were proved by Lenz’s in accordance with his theory.
, ELITE TUTORING
First Experiment
In the first experiment, he concluded that when the current in the coil flows in the circuit
the magnetic field lines are produced. As the current flows through the coil increases,
the magnetic flux will increase. The direction of the flow of induced current would be
such that it opposes when the magnetic flux increases.
Second Experiment
In the second experiment, he concluded that when the current-carrying coil is wound on
an iron rod with its left end behaving as N-pole and is moved towards the coil S, an
induced current will be produced.
Third Experiment
In the third experiment, he concluded that when the coil is pulled towards the magnetic
flux, the coil linked with it goes on decreasing which means that the area of the coil
inside the magnetic field decreases. According to Lenz’s law, the motion of the coil is
opposed when the induced current is applied in the same direction.
To produce the current force is exerted by the magnet in the loop. To oppose the
change a force must be exerted by the current on the magnet.
To better understand Lenz’s law, consider two cases:
Case 1: When a magnet is moving towards the coil.
When the north pole of the magnet is approaching towards the coil, the magnetic flux
linking to the coil increases. According to Faraday’s law of electromagnetic induction,
when there is a change in flux, an EMF, and hence current is induced in the coil and this
current will create its own magnetic field.
Now according to Lenz’s law, this magnetic field created will oppose its own or we can
say opposes the increase in flux through the coil and this is possible only if approaching
coil side attains north polarity, as we know similar poles repel each other. Once we
know the magnetic polarity of the coil side, we can easily determine the direction of the
LENZ’S LAW
Lenz’s law states that:
The induced electromotive force with different polarities induces a current whose
magnetic field opposes the change in magnetic flux through the loop in order to ensure
that original flux is maintained through the loop when current flows in it.
Named after Emil Lenz, Lenz’s law depends on the principle of conservation of energy
and Newton’s third law. It is the most convenient method to determine the direction of
the induced current. It states that the direction of an induced current is always such as
to oppose the change in the circuit or the magnetic field that produces it.
The Lenz’s Law is reflected in the formula of Faraday’s law. The negative sign is
contributed from Lenz’s law. The expression is:
△ϕ
𝑒𝑚𝑓 = −𝑁 ( )
△𝑡
Where,
Emf is the induced voltage (also known as electromotive force).
N is the number of loops.
Δϕ Change in magnetic flux.
Δt Change in time.
Lenz’s Law Experiment
To find the direction of the induced electromotive force and current we look to Lenz’s
law. Some experiments were proved by Lenz’s in accordance with his theory.
, ELITE TUTORING
First Experiment
In the first experiment, he concluded that when the current in the coil flows in the circuit
the magnetic field lines are produced. As the current flows through the coil increases,
the magnetic flux will increase. The direction of the flow of induced current would be
such that it opposes when the magnetic flux increases.
Second Experiment
In the second experiment, he concluded that when the current-carrying coil is wound on
an iron rod with its left end behaving as N-pole and is moved towards the coil S, an
induced current will be produced.
Third Experiment
In the third experiment, he concluded that when the coil is pulled towards the magnetic
flux, the coil linked with it goes on decreasing which means that the area of the coil
inside the magnetic field decreases. According to Lenz’s law, the motion of the coil is
opposed when the induced current is applied in the same direction.
To produce the current force is exerted by the magnet in the loop. To oppose the
change a force must be exerted by the current on the magnet.
To better understand Lenz’s law, consider two cases:
Case 1: When a magnet is moving towards the coil.
When the north pole of the magnet is approaching towards the coil, the magnetic flux
linking to the coil increases. According to Faraday’s law of electromagnetic induction,
when there is a change in flux, an EMF, and hence current is induced in the coil and this
current will create its own magnetic field.
Now according to Lenz’s law, this magnetic field created will oppose its own or we can
say opposes the increase in flux through the coil and this is possible only if approaching
coil side attains north polarity, as we know similar poles repel each other. Once we
know the magnetic polarity of the coil side, we can easily determine the direction of the
