1. Concept Overview
Energy transfer in electromagnetic induction is based on a simple idea: changing magnetic flux creates induced emf, and this induced emf can drive a current in a nearby coil or conductor. As a result, energy can be transferred from one system to another without direct electrical contact.
I like to think of it as energy riding on changing magnetic fields — whenever the magnetic field changes, it “carries” energy from one coil to another.
1.1. One-line idea
Mechanical energy → magnetic energy → electrical energy.
2. How Energy Is Stored and Transferred
Whenever a current flows in a coil, it creates a magnetic field around it. This field stores energy. When the current changes, the magnetic field changes, and the stored energy moves from one place to another through induction.
2.1. Magnetic field as energy storage
The magnetic field around a coil stores energy given by:
\( U = \dfrac{1}{2} L I^2 \)
This stored energy can be transferred to another coil when flux changes.
3. Energy Transfer Through Self-Induction
In self-induction, the coil stores energy in its own magnetic field. When the current changes, the coil releases or absorbs energy. This process helps smooth current in circuits and prevent sudden changes.
3.1. How it works
A decreasing current releases magnetic energy back into the circuit. An increasing current requires energy to build the magnetic field.
4. Energy Transfer Through Mutual Induction
This is the key mechanism behind transformers and many electrical machines. When current in the primary coil changes, its magnetic field changes, transferring energy to the secondary coil through changing flux.
4.1. How energy moves from coil to coil
- AC in primary → changing current.
- Changing current → changing flux in the core.
- This changing flux links with secondary coil.
- Secondary coil experiences induced emf.
- Energy is transferred from primary to secondary.
5. Power Transfer in Transformers
A transformer transfers energy from the primary to the secondary coil without direct electrical contact. The power transfer follows:
\( V_p I_p = V_s I_s \)
(ideal case)
This means the total power transferred magnetically remains equal (minus losses).
5.1. Step-up vs. step-down transfer
In step-up transformers, voltage increases but current decreases. In step-down transformers, voltage decreases but current increases. In both cases, power ideally remains the same.
6. Energy Transfer Through Eddy Currents
Eddy currents are another way energy is transferred. When changing flux passes through a metal, circular currents form. These eddy currents can produce heat or magnetic forces, transferring energy into the metal object.
6.1. Examples
- Induction heating: energy is transferred to metal through eddy currents → heating.
- Eddy current brakes: energy is transferred from motion into heat in metal plates.
7. Energy Transfer in Generators
In generators, mechanical energy is converted into electrical energy through its magnetic field. The rotating coil changes the flux linked with it, producing an induced emf.
7.1. Energy flow
Mechanical work → rotation of coil → changing flux → induced emf → electrical energy at output.
8. Energy Transfer in Motors (Reverse of Generators)
Motors work on the reverse principle of generators. Electrical energy is supplied to create a magnetic interaction, which produces mechanical motion. The device still relies on flux interaction, but energy flow is reversed.
8.1. Energy path
Electrical energy → coil currents → magnetic interaction → rotation (mechanical energy).
9. Losses During Energy Transfer
Not all energy reaches the output because some energy is lost in different forms during induction.
9.1. Common losses
- Heat due to resistance (copper losses)
- Eddy current heating in cores
- Hysteresis loss in magnetic materials
- Flux leakage
9.2. Reducing losses
Using laminated cores, soft magnetic materials, and improved coil design helps reduce losses and improve energy transfer efficiency.
10. Where We See Energy Transfer in Daily Life
Energy transfer through electromagnetic induction appears in many devices, even ones we use casually.
10.1. Examples
- Phone chargers (wireless charging)
- Transformers in adapters
- Electric stoves (induction heating)
- Power stations (generators)
- Doorbells and buzzers (coils and electromagnetic forces)