Introduction

The invention and realization of the electromagnetic induction is a landmark discovery in the science of physics. This effect, in which electric currents were produced by varying magnetic field, was discovered independently by Michael Faraday in England and Joseph Henry in America, in the first part of the nineteenth century.

Their groundbreaking research laid the theoretical foundation to the present day electric generators, transformers, and the communication systems. The classic experiments, performed by Faraday and Henry, which helped to clarify the basic principles of electromagnetic induction and made a significant contribution to the understanding of electromagnetism will be analyzed in the given discourse.

The Birth of Electromagnetic Induction

1. Early Discoveries and Motivation

Before Faraday and Henry, scientists already knew that electric currents could create magnetic fields — as shown by Hans Christian Ørsted’s discovery in 1820. But the reverse question intrigued Faraday:

“If electricity can produce magnetism, can magnetism produce electricity?”

This curiosity led to a series of experiments where Faraday and Henry independently explored how magnets and electric currents interact to induce motion and electricity.

2. About Joseph Henry

Joseph Henry (1797-1878) was an American experimental physicist, professor of physics at Princeton University and the first director of the Smithsonian Institution. He made significant improvements on creating electromagnets in which he could wind insulated wire coils over iron cores, thus creating strong magnetic fields.

Another invention that Henry came up with was the early form of the electromagnetic motor and a new and more efficient system of telegraph. Most importantly, he discovered the effect of self-induction whereby a current in one circuit can cause a current in another circuit- a principle which would later form the basis of transformers and wireless communication.

In their works, Faraday and Henry performed similar and complementary research, which led to similar conclusions made independently during the years 1831-1832.

Experiment 1 — Induction by a Moving Magnet

1. Experimental Setup

In the first experiment, Faraday was in a position to connect the coil (C₁) to galvanometer (G), which was used to sense and measure small amounts of electric currents. After that, a bar magnet was moved in the direction of and against the coil to determine whether its movement would cause the current.

Figure 1 shows that the pointer on the galvanometer deviates when the north pole of the bar magnet is moved towards the coil.

2. Observations

When the north pole of the magnet is approached to the coil, the galvanometer needle deviates, which means that an electric current has been produced in the coil.
The deflection continues as long as the magnet is moving; as soon as it stops moving the pointer goes back to zero.
On the contrary, on withdrawing the magnet out of the coil the deflection is in the opposite sense showing reversal of current induced.
The south pole motion of the magnet produces opposite deflections of the north pole.
The greater the speed of the magnetic flux the greater the deflection, which means that the induced current will also be greater.

3. Key Conclusions

When the magnet and the coil are stationary, the galvanometer shows no deflections hence supporting the fact that induction of the electromagnetic field requires relative movement.
Depending on the relative movement of the coil and magnet, i.e. whether the magnet moves towards or away, and on the polarity of the source of the magnet, the induced current will be of the same or opposite polarity.
The greater the velocity of relative motion the greater the deflection, which means that the current induced is proportional to the rate of change of the magnetic flux density.

4. Important Insight

The experiment at hand has conclusively shown that a time varying magnetic field can induce an electric current.

Faraday held that:

“The induction (generation) of electric current in the coil is due to the relative movement between the magnet and the coil.”

This rule formed the basis of the phenomenon of electromagnetic induction which up to date forms the foundation of the modern electrical technology.

Experiment 2 — Induction Between Two Coils

1. Setup and Procedure

In the second experiment, Faraday substituted the bar magnet for another coil (C₂) which was attached to a battery. Coil (C₁) continued to be attached to a galvanometer (G) as in the previous setup. When there is current flowing in coil C₂, it generates a magnetic field analogous to that which a bar magnet generates.

Refer to Figure 2 — The movement of coil C₂, which has current, causes current to flow in coil C₁.

2. Observations

When coil C₂ approaches coil C₁, there is a galvanometer deflection, indicating that C₁ gets induced with a current.
Upon the withdrawal of coil C₂, the galvanometer exhibits a deflection in the contrary direction.
The deflection holds once you're in motion, verifying that a fluctuating magnetic field (rather than a constant) produces the current.
Since C₂ does not shift position and C₁ does, we have the same observation — it is the relative motion that is occurring that is important.

3. Conclusions

This experiment proved that a changing magnetic field produced by one current-carrying coil can induce current in a nearby coil. The results paralleled those of Experiment 1 but without a permanent magnet.

The key takeaway:

“It is the relative motion between the coils that induces the electric current.”

This established that moving magnetic fields — regardless of whether they come from magnets or electric currents — can generate electricity in a conductor.

Experiment 3 — Induction Without Relative Motion

1. The Setup

Faraday then posed a new question:

“Is relative motion absolutely necessary for induction?”

To investigate this phenomenon, he used two steady coils (C₁ and C₂) placed side by side. Coil C₁ was connected to a galvanometer, and coil C₂ was connected to a battery via a tapping key (K)—the device that could quickly join or separate the circuit.

Refer to Fig. 3 — Experimental setup for Experiment 3.

2. Observations

When the tapping key K is pressed, completing the circuit in coil C₂, the galvanometer in coil C₁ shows a momentary deflection.
The needle immediately returns to zero if the key is kept pressed, even though current continues to flow steadily in C₂.
When the key is released, breaking the circuit, another momentary deflection occurs — but in the opposite direction.
The effect becomes much stronger if an iron core is inserted into the coils, as it enhances the magnetic coupling between them.

3. Key Findings

From this, Faraday deduced that:

A changing magnetic field, not necessarily motion, induces an electric current.
The induced current appears only when the magnetic field through the coil changes — during the make and break of the current in the second coil.

Thus, relative motion is not required — only a variation in magnetic flux is necessary to produce induction.

Faraday’s Law of Electromagnetic Induction

1. The Principle Summarized

From these landmark experiments, Faraday formulated the Law of Electromagnetic Induction. It states:

“An electromotive force (emf) is induced in a circuit whenever the magnetic flux through it changes, and the magnitude of the induced emf is directly proportional to the rate of change of flux.”

2. Mathematical Formulation

Mathematically, Faraday’s Law is written as:

ε=−dΦ/dt

where:

ε = induced electromotive force (emf)
Φ = magnetic flux through the coil
dΦ/dt = rate of change of magnetic flux

The negative sign represents Lenz’s Law, which states that the direction of induced current opposes the change in magnetic flux that produced it — a fundamental principle of energy conservation.

3. Understanding Magnetic Flux

Magnetic flux (Φ) through a surface is given by:

Φ=B×A×cosθ

where:

B = magnetic field strength
A = area of the loop
θ = angle between the magnetic field and the normal to the surface

A change in any of these — B, A, or θ — will induce emf according to Faraday’s Law.

Significance of Henry’s and Faraday’s Work

1. Technological Impact

The experiments of Faraday and Henry were not just theoretical triumphs — they formed the foundation for modern electrical engineering. Their principles are applied in:

Electric generators – converting mechanical energy into electrical energy using rotating magnets and coils.
Transformers – transferring electrical energy between circuits through electromagnetic induction.
Electric motors – converting electrical energy into motion.
Telecommunication systems – Henry’s improvements in electromagnets enabled efficient telegraph designs.
Inductive charging – modern wireless chargers use the same principle to transfer energy without direct contact.

2. The Legacy

The experiments conducted by Faraday and Henry proved the fact that electricity and magnetism are closely interrelated. Their findings inspired later researchers, especially James Clerk Maxwell himself, who could mathematically integrate electricity and magnetism into one beautiful concept: electromagnetism.

The Maxwell equations, based upon the discoveries made by Faraday, postulated the space of electromagnetic waves, which immediately resulted in the invention of radio, radar, and local area networks based on wireless.

Conclusion

In a sequence of simple, but deep-seated experiments, Michael Faraday and Joseph Henry discovered one of the most powerful natural laws that a varying magnetic field should produce an electric current.

Since a moving magnet near a coil of wire (Fig. 1) could induce current in the other and then the second experiment (Fig. 2) induced current in the first, and the last (Fig. 3) experiment induced current in the previous one, without any motion.

Besides revolutionizing the science, these findings had the impact of shifting the world to the age of electricity as they not only revolutionized the field of science but also heralded the shift in technology where candles would give way to electricity. This is because, as of today, all power plants, transformers, and electric motors function on the same principle initially proven by Faraday in his small laboratory which is in itself a testament to the sheer brilliance of their work.

Related Articles: