PHY C23: Applications of EM Induction

Last post of this chapter, & a nice segue to the next…

  • Applications of EM Induction
    • Eddy currents
    • Generators
    • Transformers

Eddy Currents

What are eddy currents?
Random currents induced in a conducting area via EM induction when magnetic flux linking an area changes.

Basically, when a conductor which has a shape other than a wire (such as a plate, a disk, or any other 3D shape), the current induced inside it is not a simple path. Instead, charges move with varying directions & magnitudes – just like eddies in a river.

What are the factors effecting the formation of eddy currents?

  • The shape of the conductor
  • The cross-sectional area perpendicular to the magnetic flux (A): larger A = higher induced e.m.f. = larger eddy currents
  • The thickness of the conductor: thicker conductors have more room for eddy currents to form, so larger currents form

What is the effect of eddy currents?
Energy is lost through heating.

Since currents cause heating, a large number of random currents cause a LOT of heating.
Mechanical energy is converted to electrical energy, which ends up being converted to heat.

What can we use this for?
Eddy current damping.

Mechanical systems (pendulums, rotating objects, springs) which cut magnetic flux will be DAMPED & eventually lose all their mechanical energy.


EM induction is how almost ALL of our electricity is generated.

At their simplest, generators are just coils spinning in a magnetic field.
As they periodically cut magnetic flux, an alternating e.m.f. is generated.
This is how ALTERNATING CURRENTS are created – see the next post!


We will cover these in detail in the next chapter, but basically:

  • alternating current is supplied to the primary coil, producing an alternating magnetic flux in the soft iron core
  • magnetic flux linking the secondary coil changes periodically
  • according to Faraday’ Law of EM Induction, an alternating e.m.f. is induced across the secondary coil
  • an alternating current is induced in the secondary coil

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