1. Concept Overview
Electromagnetic induction is behind many devices we use every day. The basic idea is simple: changing magnetic flux induces emf, and this induced emf can be used to produce current, motion or heat. Once I understood this core principle, a lot of machines suddenly felt easier to understand.
Almost every electrical system that involves moving magnets, alternating currents or coils uses electromagnetic induction in some way.
1.1. One-line takeaway
Changing flux transforms mechanical energy to electrical energy, electrical energy to heat, or even electric energy across coils.
2. Electric Generators
Electric generators work completely on electromagnetic induction. A coil is rotated in a magnetic field, or a magnet is rotated near a coil. Due to continuous change in magnetic flux, an alternating emf is produced.
2.1. How a generator works
As the coil rotates, the angle \( \theta \) between the magnetic field and the coil keeps changing. This changes the magnetic flux:
\( \Phi_B = B A \cos \theta \)
According to Faraday’s law, the changing flux induces an emf which becomes the AC output.
2.2. Where generators are used
Power stations, hand-crank chargers, wind turbines and bicycle dynamos — all are based on electromagnetic induction.
3. Transformers
Transformers transfer electrical energy between two coils without any direct electrical connection. They work on mutual induction, where alternating current in the primary coil produces changing flux that induces emf in the secondary coil.
3.1. Working principle
The AC current in the primary coil changes rapidly with time, causing the magnetic flux in the core to change:
\( \Phi_B \, \text{changes with time} \rightarrow \varepsilon_2 = -M \dfrac{dI_1}{dt} \)
This induced emf in the secondary coil can be higher or lower depending on the number of turns.
3.2. Uses of transformers
They are used in power transmission, adapters, chargers, audio systems, and almost every device that needs voltage conversion.
4. Induction Cookers
Induction cookers use high-frequency alternating currents in a coil to produce rapidly changing magnetic fields. These changing fields induce eddy currents in the metal base of the cooking vessel. The eddy currents heat the vessel directly.
4.1. Why induction cooking is efficient
The heat is generated only in the vessel, not in the cooker surface. Eddy currents are strong because of rapid flux changes, allowing fast heating.
4.2. Everyday advantage
Safe to touch, fast cooking, and high energy efficiency compared to gas stoves.
5. Eddy Current Brakes
In eddy current brakes, a moving metal plate passes through a strong magnetic field. The changing flux induces circulating eddy currents in the metal. These currents oppose the motion, providing smooth braking without physical contact.
5.1. Where eddy current braking is used
Roller coasters, electric trains, elevators, and exercise machines.
6. Electric Meters and Measuring Instruments
Old-style energy meters and many measuring instruments use electromagnetic induction to detect rotation, deflection or damping.
6.1. Energy meters
Alternating currents produce changing flux which induces eddy currents in a rotating disc. These eddy currents produce torque proportional to power consumption.
6.2. Galvanometers with magnetic damping
To make the pointer settle quickly, eddy currents are used to oppose unwanted oscillations. This prevents overshooting.
7. Induction Motors
Induction motors use changing magnetic fields to induce currents in the rotor. These induced currents create their own magnetic field, which interacts with the stator’s field and produces torque. No direct electrical connection to the rotor is needed.
7.1. Why induction motors are popular
No brushes or commutators, low maintenance, and efficient operation — perfect for fans, pumps and industrial machines.
8. Wireless Charging
Wireless chargers use mutual induction. The charging pad coil carries alternating current, creating a changing magnetic field. The device coil picks up this changing flux and an induced emf charges the battery.
8.1. Why wireless charging works only at close distance
Mutual induction becomes weaker with distance, so the coils must be close and aligned properly.
9. Metal Detectors
Metal detectors use induction principles to detect hidden metals. An alternating magnetic field induces eddy currents in nearby metal objects. These eddy currents create their own magnetic fields that disturb the detector’s coil, signalling the presence of metal.
9.1. Where used
Airports, security checkpoints, archaeology and treasure hunting devices.
10. Induction Heating Systems
Induction heating uses rapidly changing magnetic fields to induce strong eddy currents in metal parts. This heats them quickly and uniformly without direct contact.
10.1. Where induction heating is applied
Used in metal hardening, forging, soldering, and industrial heating processes.