- Slides: 32
► ► ► ► Lodestones Bar magnet Audio tape and magnet Iron shavings in Lucite Old CRT Coil, power supply, & compass Motor Speaker Paint stick, magnet, and electromagnet Magnet + coil + demo galvonometer DC Ammeter, two coils, demo galvonometer Two coils, DC Ammeter, power supply relay Buzzer Transformer
Magnetism… was used in the 12 th century when it was discovered that an iron -rich magnetic material would align itself with Polaris (the north star). This mineral, magnetite, was the first compass.
► The Chinese used a compass around 200 B. C to align buildings for best harmony. http: //www. grand-illusions. com/compass. htm ► The Chinese are considered the first people to use the compass for navigation in the East and the Venetians were the first to use it in the West. www. aaei. org
An auspicious moment in 1820… Hans Christian Oersted, a Danish Physics professor, was demonstrating electricity when he noticed that whenever his battery was connected to a loop of wire, a nearby compass needle would twitch!!! His experiment showed that current in a wire has a magnetic field around it. Oersted discovered that electricity produces a magnetic field.
http: //www. gcse. com Oersted discovered that electricity produces a magnetic field.
Electromagnets in Industrial Applications istockphoto http: //www. storchmagnetics. com
► Static electric charge produces an electric field. ► Moving electric charge produces a magnetic field.
Electromagnets used in Tape Players The electromagnet consists of an iron core wrapped with wire, as shown in the figure. During recording, the audio signal is sent through the coil of wire to create a magnetic field. A – Tape How. Stuff. Works This field magnetizes the magnetic oxide on the tape.
CRT coils “steers” electron beam
All magnetism arises from moving charge A Permanent Magnet is made from a material that has many atoms that act like tiny bar magnets, where all the atomic magnets are lined up producing bulk magnetism. N S
Permanent Magnet N N N S S N S N S N N S S
Magnets Paired electrons spin in opposite directions, their magnetic fields cancel one another out. Atoms of ferromagnetic elements, on the other hand, have several unpaired electrons that have the same spin. These atoms act like tiny bar magnets. Iron, for example, has four unpaired electrons with the same spin. Because they have no opposing fields to cancel their effects, Iron is magnetic. Iron and other ferromagnetic materials are crystalline. As they cool from a molten state, groups of atoms can line up within the crystal structure, forming a permanent magnet. Magnets attract materials that have atomic magnets. Howstuffworks
Michael Faraday was a self-taught scientist fascinated with science. In 1831 he showed the reverse of Oersted’s experiment: That electricity flows in a wire when a magnet is moved relative to the wire. This is called Electromagnetic Induction
www. physics. uiowa. edu
The Generator This generator delivers continuous AC current. http: //www. powerstandards. com
Generator converts Kinetic Energy into Electrical Energy http: //sol. sci. uop. edu
Current alternates http: //www. physchem. co. za
Motors are generators in reverse The current direction in the wire changes with every half rotation. The wire is an electromagnet and aligns with the magnetic field of the permanent magnet. As soon as the wire aligns, current then flows in the opposite direction because of the gap in the commutator. This causes the wire to flip over 180 degrees. The constantly changing magnetic field, causes the coil to continue to realign. Brittanicakids
Faraday demonstrates the Transformer Two coils very close together. Current in the first coil, sets up a magnetic field. This magnetic field induces current in the second coil. The transformer allows the stepping up or down of current based on the ratio of windings in the first coil to the second coil. Wikipedia
Steam Powered Generators By the 1850’s coal was burned to make steam which in turn was used to turn a generator to produce continuous current. Electricity meant instant, on demand clean power (never mind the coal burning in the next building).
Thomas Edison was determined to provide electricity to light homes. Edison was convinced that electricity should be DC (direct current). DC voltage can not be easily stepped up to high voltages using transformers, therefore it was impractical for supplying electricity over long distances.
DC makes an attempt… In the 1880’s there were a few DC power stations in England
Nikola Tesla invents a practical AC Motor www. sciencemuseum. org. uk
AC wins by the 1890’s AC power stations that generate power at 10, 000 volts are built. The voltage is stepped down using transformers. This is similar to today’s technology. Oregon Historical Society http: //www. energymanagertraining. com
Power Grid is based on AC voltage This allows stepping up and stepping down of voltage using transformers. http: //www. windows. ucar. edu
Maxwell’s Equations James Clerk Maxwell took Faraday’s discoveries and put them into equations. The four equations state: 1. Like charges repel, unlike charges attract 2. Magnetic fields always have two poles (positive and negative) 3. A moving/changing magnetic field produces an electric field. 4. Moving electrical charge (current) produces a magnetic field.
Ways to make electricity ► Move a magnet near a conductor ► Move a conductor (wire) near a magnet ► Made an electromagnet (coil with current in it). Move the electromagnet near a conductor. ► Put two coils next to each other. Pass current in one coil. Other coil has current if first coil’s current is changing. ► Rotate a coil inside a permanent magnetic field. Coil will have a back and forth current.
Maxwell predicts Electromagnetic Radiation An electromagnetic wave exists when the changing magnetic field causes an electric field which then causes another magnetic field, and so on forever. These oscillating fields together form an electromagnetic wave. An electromagnetic wave will travel at 186, 000 miles/sec. and continue on forever until absorbed. Wikipedia. com
Heinrich Hertz demonstrates in 1888 the existence of electromagnetic radiation
A non-turbine Generator (Micro Wind Generator) http: //link. brightcove. com/services/player/bcpid 1214137061? bctid=1233395616 And where did this idea come from? http: //www. youtube. com/watch? v=ASd 0 t 3 n 8 Bnc
Sources ► The Sciences- 5 e, Trefil and Hazen ► A History of Great Inventions, James Dyson ► http: //www. physclips. unsw. edu. au/jw/electr icmotors. html