Electromagnetism

1. Electromagnetism • Unit 10

2. History • Originally electricity & magnetism were thought of as 2 separate forces. • Key developments during the early 19th century led to a unified theory in which the phenomena of electricity & magnetism are known as electromagnetism.

3. Hans Christian Ørsted • While preparing for a lecture, Ørsted, a Danish physicist, made a surprising observation. • Ørsted noticed that a compass needle deflected from magnetic north when the electric current from a battery was switched on & off. • This demonstrated that electric current passing through a wire produces a magnetic field; confirming the direct relationship between electricity & magnetism.

4. Hans Christian Ørsted • However, Ørsted didn’t suggest an explanation nor derive a mathematical expression to describe his observations. • Despite this, Ørsted published his findings, and is credited with proving that electric current produces a magnetic field.

5. André-Marie Ampère • French physicist, Ampère was influenced by Ørsted’s work and through his own research, he developed a mathematical formula to describe the relationship between magnetic forces & electrical current. • The SI unit for current (amps) were named after him.

6. Michael Faraday • Although Faraday, an English physicist, received little formal education, he was one of the most influential scientists in history. • Historians refer to him as having been the best experimentalist in the history of science.

7. Michael Faraday • It was Faraday’s research on magnetic fields around a conducting wire that led him to establish the basis for the concept of the electromagnetic field. • Faraday also discovered the concept of electromagnetic induction. • The SI unit for capacitance (farads) are named after him.

8. Electromagnetic Induction • An electric current produces a magnetic field, and vice versa, a changing magnetic field produces an electric current! • This motion is said to induce an electric current (EMF) through the coil of wire. Moving a magnet through a coil of wire (solenoid)produces an electric current

9. Electromagnetic Induction

10. Solenoid • A solenoid is simply a coil of wire. • The solenoid is the basis for the electromagnet.

11. Electromagnets • Electromagnet is a magnet in which the magnetic field is produced by the flow of electric charge. • Wrapping the wire around a metal core concentrates or increases the magnetic field due to the additive effect of each turn of wire.

12. Electromagnets

13. Faraday’s Law of Induction • ANY change in a magnetic environment of a coil of wire will induce a flow of charge (EMF) in the coil. ∆B – change in magnetic field strength Moving coil into or out of B Moving a magnet toward or away from coil Rotating coil relative to the magnet http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html

14. Faraday’s Law of Induction EMF - electromagnetic field N represents the number of loops in the wire ΔΦB is the change in magnetic flux

15. Lenz’s Law • When an electric current is generated by a change in magnetic flux according to Faraday’s Law, the induced magnetic field opposes the motion of the magnet.

16. Lenz’s Law The (-) indicates that the induced magnetic field (EMF) is always opposite the change in magnetic flux (ΔΦB) In other words, the magnetic field points in the opposite direction of the change in magnetic flux.

17. Lenz’s Law What is the direction of the magnetic field produced by the induced current? (a) ? down (b) ? up

18. Lenz’s Law The induced magnetic field repels the approaching magnet The induced magnetic field attracts the departing magnet

19. James Clerk Maxwell • Maxwell, a Scottish theoretical physicist, expanded upon Faraday’s research to unify electricity & magnetism. • Maxwell’s most prominent achievement is the complete & comprehensive theory which unifies electricity, magnetism, & light.

20. Maxwell’s Equations • In a set of 4 elegant equations, Maxwell demonstrated that electricity, magnetism, & light are all a product of the electromagnetic field!

21. James Clerk Maxwell • In addition, Maxwell demonstrated that magnetic & electrical fields are self-reinforcing and travel at the speed of light (c).

22. James Clerk Maxwell • Thus, he concluded that light energy travels in the form of opposite but supporting electrical & magnetic fields in the form of self-propagating electromagnetic waves!

23. James Clerk Maxwell • Maxwell’s achievements in electromagnetism is considered the greatest unification in physics since Newton’s Laws!

24. Electromagnetic Radiation • Electromagnetic radiation, also known as light, is energy that is propagated (moving) through space in the form of EM waves such as radio waves, visible light, & gamma rays. • The wavelength of light determines its energy & characteristics.

25. Electromagnetic Spectrum

26. Electric Motor • An electric motor is an electric machine that converts electrical energy mechanical energy. • They operate through the interaction between a magnetic field and winding electric currents to generate force.

27. Electric Motor • Inside the electric motor the attracting and repelling forces of magnets create rotational motion. • Therefore using a electromagnetic fields to generate mechanical motion! electrical energy mechanical energy. http://www.youtube.com/watch?v=MnQXnEiIUI8

28. Electric Generator • An electric generator is a device that converts mechanical energy electrical energy. • Mechanical energy is used to force electric current to flow through an external circuit. • A magnet is moved near a wire to create a steady flow of charge. Mechanical energy electrical energy.

30. Electric Transformers • An electric transformer is a device that changes the voltage of incoming electricity to meet the needs of specific electric devices. High voltage Low voltage - OR - Low voltage High voltage

31. Anatomy of a Transformer

32. Voltage to Coil Ratios Primary voltage Secondary voltage Primary coil turns Secondary coil turns The ratio of the voltage to the # of coil turns in the primary coil (input side) is equal to the ratio in the secondary coil (output side) 1° Voltage 1° Turns 2° Voltage 2° Turns

33. Step-down Transformer • Step-down transformers are designed to reduce voltage. 1° Coil Turns > 2° Coil Turns Output: Low voltage High current. Input: High voltage Low current. Input Power Output Power

34. Step-up Transformer • Step-up transformers are designed to increase voltage. 1° Coil Turns < 2° Coil Turns Output: High voltage Low current. Input: Low voltage High current. Input Power Output Power

35. Nanoscale Motors

36. How to Cite a Website in MLA • Structure: Last name, First name. "Article Title." Website Title. Publisher of Website, Day Month Year article was published. Web. Day Month Year article was accessed. <URL>. • Example:Cain, Kevin. "The Negative Effects of Facebook on Communication." Social Media Today RSS N.p., 29 June 2012. Web. 02 Jan. 2013.

37. Links http://abyss.uoregon.edu/~js/21st_century_science/lectures/lec04.html How to make a motor http://www.education.com/science-fair/article/no-frills-motor/ http://www.pbslearningmedia.org/resource/psu06-nano.sci.text.lpmotorms/turning-electricity-and-magnetism-into-mechanical-work-with-a-simple-motor-ms/ Animations http://www.animations.physics.unsw.edu.au/jw/electricmotors.html