► Lodestones ► Bar magnet ► Audio tape and magnet ► Iron shavings in Lucite ► Old CRT ► Coil, power supply, & compass ► Motor ► Paint stick, magnet, and electromagnet ► DC Ammeter, coil, magnet ► 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. ► 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.

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.

Oersted discovered that electricity produces a magnetic field.

istockphoto Electromagnets in Industrial Applications

► Static electric charge produces an electric field. ► Moving electric charge produces a magnetic field.

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 S N S N S N S N S N S N S N S N 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. Iron, for example, has four unpaired electrons with the same spin. Because they have no opposing fields to cancel their effects, these electrons have an orbital magnetic moment. Iron and other ferromagnetic materials are crystalline. As they cool from a molten state, groups of atoms line up within the crystal structure, forming a permanent magnet. Magnets attract materials that have unpaired electrons. Howstuffworks

Electromagnets used in Tape Players A – Tape HowStuffWorks 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. This field magnetizes the magnetic oxide on the tape.

Sea floor as a magnetic tape Earth’s outer core is liquid. The earth’s magnetic field reverses itself periodically. The rocks at oceanic spreading centers have atomic magnets that are aligned with what the earth’s polarity was at the time the rock solidified.

CRT coils “steers” electron beam

The Motor The motor is a rotating loop of wire with current in it that spins in the presence of a magnetic field. The Commutator has two rotating contacts with a gap in the middle. The brushes allow the contacts to slide while still making electrical contact. The current changes direction every 180 o

The Speaker

Michael Faraday Faraday was a self-taught scientist. In 1831 he showed that electricity is created from a changing magnetic field. Electromagnetic Induction Electromagnetic Induction

The Generator This generator delivers continuous AC current.

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 the AC Motor

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

Power Grid is based on AC voltage This allows stepping up and stepping down of voltage using transformers.

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) negative) 3. A moving/changing magnetic field produces an electric field. 4. Moving electrical charge (current) produces a magnetic field. magnetic field.

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

demonstrates in 1888 the existence of electromagnetic radiation Heinrich Hertz demonstrates in 1888 the existence of electromagnetic radiation

A non-turbine Generator (Micro Wind Generator) And where did this idea come from?

► The Sciences- 5e, Trefil and Hazen ► A History of Great Inventions, James Dyson ► icmotors.html Sources