Home » Technical Description

Attribution-NonCommercial-ShareAlike 4.0 International

Except where otherwise noted, content on this site is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International license.

Technical Description

Mutual Generation: Electromagnetic Induction

By Emelie Coello

hi

The Basics

  • Current: flow of free electrons through a conductor, measured in ampères (A)
  • Voltage: electrical pressure in a circuit that drives electrons creating current, also known as electromotive force (EMF) or potential difference, measured in volts (V)
  • Resistance: friction in relation to current, measured in ohms (𝝮)

Figure 1: Ohm’s Law

  • Magnetic flux: entire group of magnetic field lines leaving the north pole, comparable to current  
  • Magnetomotive Force (MMF): amount of magnetic pressure in a circuit that drives magnetic field lines creating flux, comparable to voltage 
  • Permeability: measure of an object’s ease of passage for molecules or magnetic lines of force,     comparable to conductivity

Figure 2: Stronger magnetic field = more lines of force = more flux

  • Electromagnet: current passing through a coil of wire wrapped around a metal core creating a strong magnetic field
  • Direct current (DC): current that goes in only one direction in a circuit
  • Alternating current (AC): current that goes back and forth in a circuit 

Figure 3: An electromagnet

  • Inductance: generation of current or voltage in a conductor by varying the magnetic field around it or generation of a magnetic field in a conductor due to alternating current, measured in henrys (H)
  • Eddy current: current loops formed over conductor surfaces due to changing magnetic flux, named after eddies which are another term for whirlpools

ヾ( ˃ᴗ˂ )◞ • *✰

A Web of Discoveries

1820hiHans Christian Ørsted noted a current carrying wire’s ability to deflect a compass needle during one of his lectures at Copenhagen University. François Arago replicated Ørstead’s experiment for his fellow scientists and his friend, André-Marie Ampère, at the French Academy of Sciences. Ampère was then inspired to conduct his own experiments. He found that two parallel current carrying wires attract each other as their currents go in the same direction and repel each other as their currents go in the opposite direction. So, he formulated a theory which would become Ampère’s Law: current creates magnetic fields proportional to itself.  

Figure 4: Positive/negative current’s deflection of a compass needle

1824hiFrançois Arago discovered rotational magnetism which is induced when a non-magnetic conductor is rotated, so he also discovered eddy currents unknowingly.

1826hiWilliam Sturgeon demonstrated his iron core electromagnet capable of holding a lot of weight at the Albany Academy. Joseph Henry, a former student and then professor at the academy, wanted to improve it and in doing so discovered self-inductance in 1832. The unit for inductance, henrys, is named after him.

1831hiMichael Faraday’s magnet experiments inspired by Ørsted and Arago led him to proving his own theory which would become Faraday’s Law of Induction: the induced voltage in a conductor is proportional to the rate of change of magnetic flux. 

Figure 5: Faraday’s Law in action

1834hiHeinrich Friedrich Emil Lenz’s experiments led him to formulate Lenz’s Law: if a magnetic flux through a loop changes, an eddy current is induced in the loop which generates a magnetic field to oppose the change in magnetic flux. However, Lenz didn’t use the term eddy current. The symbol for inductance is L for Lenz.

1855hiLéon Foucault fleshed out Arago’s and Lenz’s ideas after conducting experiments involving induction of current within a moving conductor in a magnetic field. He explained his findings with the term eddy current which is also called Foucault’s current in his honor.

Figure 6: Eddy current formation

ඞ ඞ ඞ ඞ ඞ ඞ ඞ

The Breakdown

Inductors convert electrical energy to magnetic energy once current flows through. Then they keep the magnetic energy in a magnetic field until that collapses due to the removal of current, causing a conversion back into electrical energy. They oppose change in current, so they will pass DC but impede AC.

Self-inductance occurs when current is increased or decreased as its magnetic field does the same and in doing so induces a current that goes in the opposite direction.

Mutual inductance occurs when two inductors are close enough to share a bit of a mutual magnetic field, so some of the energy in one inductor is magnetically transferred to the other. 

capiche?

A Variety of Applications

  • MRI (Magnetic Resonance Imaging) machines
  • Generators
  • Electric motors
  • Transformers
  • Induction cooking
  • Loudspeakers
  • Wireless charging
  • Headphones
  • Electric guitars
  • Tape recorders
  • Metal detectors
  • Particle accelerators

Figure 7: Lenz’s Law in action

teehee

References

(n.d.). Ohm’s Law: Diagram, Equation & Experiment. StudiousGuy. https://studiousguy.com/ohms-law-diagram-equation-experiment/

(n.d.). Magnetic Induction – StickMan Physics. StickMan Physics. https://stickmanphysics.com/stickman-physics-home/magnets-and-magnetism/magnetic-induction/

(2019, May 14). 7 Major Contributions of Hans Christian Oersted. Learnodo Newtonic. https://learnodo-newtonic.com/oersted-contribution

(2021, February 28). Sussing Out Solenoids With Dot and Cross. E=mc2andallthat. https://physicsteacher.blog/2021/02/28/sussing-out-solenoids-with-dot-and-cross/

(2024, January 24). Faraday’s Law | Formula + Definition. Worksheets Planet. https://www.worksheetsplanet.com/faradays-law-formula-definition/

Advanced Quality Centre. (2020, December 15). What is eddy current testing in NDT? Nondestructive Testing service providers. https://ndtcenter.blogspot.com/2020/12/what-is-eddy-current-testing-in-ndt.html.

Beninati, P. (2021, September). What are the fundamentals of electricity? [Slide show]. Queens Technical High School

Feldmann, C. & TU Delft. (2020, August 4). Faraday’s Law [Video]. YouTube. https://www.youtube.com/watch?v=SrgQwAbeGaA

National High Magnetic Field Laboratory. (n.d.). Joseph Henry. National MagLab. https://nationalmaglab.org/magnet-academy/history-of-electricity-magnetism/pioneers/joseph-henry/

Ponchon, P. [Philippe Ponchon] & Musée Ampère. (2020, September 2). 1820, André-Marie Ampère discovers electrodynamics [Video]. YouTube. https://www.youtube.com/watch?v=x8BVwosjI1Y

Raushan, M. (2023, January). To understand electrical and magnetic properties [Slide show]. Queens Technical High School

Stevens, M. & D!NG. (2018, March 24). Lenz’s Law [Video]. YouTube. https://www.youtube.com/watch?v=QwUq8xM_8bY

Sultan, A. [Ayman Sultan]. (2017, July 3). ‪Eddy Currents and Lenz s Law‬‏. YouTube. https://m.youtube.com/watch?v=GxGydxeeiFA
Zurek, S. (n.d.). History of electromagnetism. Encyclopedia Magnetica™. https://www.e-magnetica.pl/doku.php/history_of_electromagnetism