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Electromagnetic Induction: Exploring Coils, Transformers, and Inductors

Discover the principles of electromagnetic induction, learn about inductance in coils, and explore the workings of transformers. Understand the symbols, calculations, and applications related to inductors and transformers in electrical circuits.

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Electromagnetic Induction: Exploring Coils, Transformers, and Inductors

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  1. Electromagnetic Induction Chapter 12

  2. Objectives • Demonstrate how to induce a voltage using a coil and a magnet. • Explain four things that affect the amount of inductance in a coil. • Draw the symbols for a fixed and adjustable inductor. • Calculate the power and current on the secondary of a transformer.

  3. Induced Voltage • Magnet pushed into coil produces slight current • Changing magnetic field induces voltage in coil • Voltage is called induced emf • Counter-electromotive force (cemf) opposes applied voltage

  4. Induced Voltage (continued) • Current creates magnetic field around the coil • Current in ac circuits is always changing • Magnetic coupling

  5. Inductance • Opposition to change in current flow • Circuit with coil takes longer to reach its maximum current than same circuit without coil • Coil in dc circuit only affects circuit when switch is opened or closed • Coil in ac circuit constantly affects circuit because current is always changing

  6. Inductors • Cores • Units • Applications • Factors Inductor Symbols

  7. Inductor Cores and Units • Inductors are made of coils of copper wire over different types of cores • One henry (H)results from one volt being induced while current is changing at rate of one ampere per second

  8. Inductor Applications • Used in radios for tuning circuits, switching power supplies, and where there is need to smooth out ac ripple • Intersections use inductors to change traffic lights

  9. Inductor Factors • Several things that impact inductance in coils are illustrated here

  10. Inductors in Series • Inductor values are given in henrys (H), millihenrys (mH), and microhenrys (µH) • Formula for total inductance for inductors in series is LT = L1 + L2 + L3 + …

  11. Inductors in Parallel • Inductors have no effect on dc circuits except when switches are closing and opening • Formula for inductors in parallel

  12. Mutual Inductance • Mutual inductance results from ac flowing in coil 1, which will induce voltage across coil 2 • Formula for mutual inductance

  13. Transformers • Primary winding • Secondary winding • Symbols for transformers

  14. Transformers (continued) • Names are based on core design used for attaching windings • Closed form transformer • Shell-form transformer

  15. Transformers (continued) • Laminated cores • Step-up transformers • Step-down transformers • Tapped • Phase relationships • High-voltage • Current clamp use

  16. Laminated Cores • Thin strips of metal are laminated and stacked together to build core • Eddy current flow is reduced by using laminated cores • Eddy currents cause excessive heat

  17. Step-Up Transformers • Secondary voltage is larger than primary voltage • Relationship between voltage and number of turns

  18. Step-Down Transformers • Primary voltage is larger than secondary voltage • Use same turns ratio formula • Majority of transformers in electronics field will be step-down

  19. Tapped Transformers • A tap is connected to secondary winding • Allows turns ratio between primary and secondary to be changed, which yields additional voltages

  20. Phase Relationships • “Like-wound” transformers have two dots placed above winding schematic • “Unlike-wound” transformers have two dots placed at opposite ends of primary and secondary

  21. Voltage-Current Relationships • If transformers are 100% efficient and have no losses • PP = PS • Given voltage of primary and secondary, and primary current, it is possible to calculate secondary current

  22. High-Voltage Transformers • High-voltage transformers have ratings of over 24,000 volt-amperes (VA) • Volt-ampere is found by multiplying volts and amps of primary • Primary of 12,000 volts and two (2) amps would provide 24,000 VA • Unit is called 24 kVA transformer

  23. Math Focus: Square Roots • Related to the base of a number that is squared • A square root of a number is the number that when multiplied by itself gives that value • Do other computations in the equation before finding the square root

  24. Practical Application • Current lamp • Current probe • Placed over the wire to measure circuit current • Uses principles of induction and transformer action

  25. Review • How can voltage be induced with a coil and magnet? • Either by passing a magnet through the coil or by holding the magnet stationary and moving the coil over it.

  26. Review • What are the four things that affect the amount of inductance in a coil? • Number of turns of wire in the coil, type of core, the cross-sectional area of the core, and the length of coil compared to the number of turns of wire.

  27. Review • How is the symbol for a continuously adjustable inductor different from the symbol for a basic inductor? • An arrow runs diagonally through the coil.

  28. Review In a transformer, what is the equation used to express the relationship between voltage and the number of turns?

  29. Activities • List the places you find transformers around your house. • Discuss why industrial plants operate so much of their equipment at 460 V instead of 120 V. • Explain the type of voltage used to operate the large electromagnets found in junkyards.

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