Electromagnetic induction leads to eddy currents in conductors exposed to changing magnetic fields. These currents have practical applications in magnetic damping, electromagnetic braking, and non-destructive testing of materials.

Induction heating uses eddy currents to generate heat in conductive objects. This principle is applied in induction cooktops and metal detectors. Transformers use electromagnetic induction to transfer energy between circuits, enabling efficient power transmission and distribution.

Eddy Currents and Applications

Electromagnetic Induction in Conductors

• Eddy currents arise when a conductor experiences a changing magnetic field, inducing circular electric currents within the conductor
• These currents flow in closed loops perpendicular to the magnetic field, similar to the way water eddies form in a stream
• The strength of eddy currents depends on the conductivity of the material, the strength of the magnetic field, and the rate of change of the magnetic field
• Eddy currents generate their own magnetic fields that oppose the original magnetic field, following Lenz's law (opposing the change that created them)

Applications of Eddy Currents

• Magnetic damping utilizes eddy currents to slow down the motion of a conductor moving through a magnetic field
  • The induced eddy currents create a drag force that opposes the motion, converting kinetic energy into heat
  • Used in applications such as pendulum damping, roller coasters, and seismographs to reduce unwanted oscillations
• Electromagnetic braking relies on eddy currents to slow down or stop a moving object
  • When a conductor moves through a strong magnetic field, the induced eddy currents create a braking force
  • Employed in systems like train brakes, electric meters, and some exercise equipment to provide non-contact braking
• Eddy current testing is a non-destructive method for detecting flaws or cracks in conductive materials
  • A probe with an alternating current induces eddy currents in the test material
  • Flaws or cracks disrupt the eddy current flow, which can be detected by measuring changes in the probe's impedance

Induction Heating

Principles of Induction Heating

• Induction heating is a process that uses electromagnetic induction to generate heat in a conductive material
• An alternating current flowing through a coil creates a rapidly changing magnetic field
• When a conductive object is placed within this field, eddy currents are induced in the object
• The resistance of the material to these eddy currents leads to Joule heating, causing the object to heat up

Applications of Induction Heating

• Induction cooktops utilize induction heating to directly heat pots and pans made of ferromagnetic materials
  • A coil beneath the cooktop surface generates a high-frequency magnetic field
  • Eddy currents induced in the cookware cause it to heat up, while the cooktop surface remains cool
  • Offers faster heating, improved energy efficiency, and enhanced safety compared to traditional cooking methods
• Metal detectors employ induction principles to detect metallic objects
  • A transmitting coil generates an alternating magnetic field that penetrates the ground
  • When a metal object is present, it becomes magnetized and creates its own magnetic field
  • A receiving coil detects this secondary field, indicating the presence of metal
  • Used in security screening, archaeological surveys, and hobby treasure hunting

Transformers

Principles of Transformers

• Transformers are devices that transfer electrical energy between two or more circuits through electromagnetic induction
• They consist of two or more coils of wire (windings) wrapped around a common core made of a ferromagnetic material (laminated iron or ferrite)
• The primary winding is connected to an alternating current (AC) source, which creates a changing magnetic field in the core
• This changing magnetic field induces an electromotive force (EMF) in the secondary winding through mutual induction
• The voltage ratio between the primary and secondary windings is proportional to the ratio of the number of turns in each winding: $\frac{V_p}{V_s} = \frac{N_p}{N_s}$

Applications of Transformers

• Power transmission systems rely on transformers to efficiently transfer electrical energy over long distances
  • Step-up transformers increase the voltage and decrease the current before transmission, minimizing power losses
  • Step-down transformers reduce the voltage to safe levels for distribution and consumption
  • This allows for the economical transmission of power from generating stations to homes and businesses
• Isolation transformers provide electrical isolation between two circuits while allowing power to be transferred
  • The primary and secondary windings are electrically isolated, preventing direct current flow between them
  • Used in medical equipment, audio systems, and power supplies to enhance safety and reduce noise
• Impedance matching transformers adapt the impedance of a source to the impedance of a load for maximum power transfer
  • The turns ratio is chosen to match the source and load impedances: $\frac{N_p}{N_s} = \sqrt{\frac{Z_p}{Z_s}}$
  • Commonly used in audio systems (microphones, speakers) and antenna circuits to optimize signal transmission and reception