Spring 2006 Harvard Science, A 52 FHA+MBM Lecture 17 1

Motors, Electrical Devices, and Videos of Lighting and

Wiring the Nation

Science A 52 Lecture 17; April 12, 2006

Spring 2006 Harvard Science, A 52 FHA+MBM Lecture 17 2

Refrigeration

•Refrigeration is perhaps the largest single consumer of electrical power in the US.

•There is a very large central chilling plant below the Science Center that is electrical driven.

•We can visit the plant but we first need some materialon how the refrigeration cycle works.

•We need to plan the day for the 45 minute visit preceded by a 15 minute lecture. When will it be?

Spring 2006 Harvard Science, A 52 FHA+MBM Lecture 17 3

Early Electrical Devices.

•Telegraph

•Electric motors and streetcars and railroads

Spring 2006 Harvard Science, A 52 FHA+MBM Lecture 17 4

Early use of Electricity

Certainly one of the earliest commercial use of electricity was the telegraph. In this country Joseph Henry was exploringthe connection between current and magnetic field.It is certain that Joseph Henry was important to the history of the telegraph in two ways. First, he was responsible for major discoveries in electromagnetism, most significantly the means of constructing electromagnets that were powerful enough to transform electrical energy into useful mechanical work at a distance. Much of Morse's telegraph did indeed rest upon Henry's discovery of the principles underlying the operation of such magnets. See the site below for more information.

http://www.si.edu/archives/ihd/jhp/joseph21.htm

Spring 2006 Harvard Science, A 52 FHA+MBM Lecture 17 5

Early use of ElectricityMost important inventions are covered in controversy about who is responsible for what. Certainly this is true for the telegraph. Most high school text book attribute the telegraph to Samuel F.B. Morse who was also a will regarded fine arts painter.For more on the telegraph see:See http://inventors.about.com/library/inventors/bltelegraph.htm While a professor of arts and design at New York University in 1835, Samuel Morse proved that signals could be transmittedby wire. He used pulses of current to deflect an electromagnet, which moved a marker to produce written codes on a strip of paper - the invention of Morse Code. The followingyear, the device was modified to emboss the paper with dots and dashes. He gave a public demonstration in 1838, but it was not until five years later that Congress (reflecting public apathy) funded $30,000 to construct an experimental telegraph line from Washington to Baltimore, a distance of 40 miles.

Spring 2006 Harvard Science, A 52 FHA+MBM Lecture 17 6

Early use of Electricity

http://www.sparkmuseum.com/TELEGRAPH.HTM

A visit to the site below will show you some of the development of telegraph keys and devices. Note thatThe Morse code did not come at the very beginning butEvolved as other methods proved less useful.

Spring 2006 Harvard Science, A 52 FHA+MBM Lecture 17 7

With the development of the railroad it followed naturally that cities would find it was easier to move a carriage of people on rails rather than just pulling a carriage down dirt roads.

The Massachusetts Historical Society has a nice picture and story of “horse power” moving a street car.

http://www.masshist.org/cabinet/june2003/june2003.htm There is more at:http://www.mbta.com/insidethet/taag_history.aspTransportation was an early adopter of electrical power.

Street railroads - the streetcar.

Spring 2006 Harvard Science, A 52 FHA+MBM Lecture 17 8

Let us look at simulations electrical current, motors, and generators

There are many great simulations. Let us take a lookAt current flow in a wire.http://www.walter-fendt.de/ph14e/mfwire.htm

Look at the force on a current carrying wire in a magnetic field.http://www.walter-fendt.de/ph14e/lorentzforce.htm

Look at a DC electrical motor.http://www.walter-fendt.de/ph14e/electricmotor.htm

Look at generatorshttp://www.walter-fendt.de/ph14e/generator_e.htm

Spring 2006 Harvard Science, A 52 FHA+MBM Lecture 17 9

A more analytical look at motors and generators

This site is a very completer site for most ideas of physics.We will look just at motors;http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

You can work you way through this site to be sure that youunderstand to a certain extent electrical currents and magnetic fields

Spring 2006 Harvard Science, A 52 FHA+MBM Lecture 17 10

Videos

• A portion of Edison’s Miracle of Light - American Experience -WGBH

• A small portion of Electric Nation - PBS Home Video

Spring 2006 Harvard Science, A 52 FHA+MBM Lecture 17 11

What to look for in the videos•From 1831 and the discovery of induction by Faraday and Henry only the electrical telegraph was invented.

•To use the analogy of Computer Science, the world was waiting for the killer application.

•That application was the light bulb and the lighting system.

Spring 2006 Harvard Science, A 52 FHA+MBM Lecture 17 12

Edison• Others had made light bulbs before him, but

they did not last long - minutes or a few hours - the filament always burned through in a few minutes.

• Modern bulbs use a tungsten filament in a nitrogen atmosphere, but Edison did not have tungsten as you will see.

• What Edison did have was a vision of the entire system - the light bulb,the generators, and the distribution system including the metering to pay for the lighting system.

Spring 2006 Harvard Science, A 52 FHA+MBM Lecture 17 13

Edison - continued

Edison combined all of the features necessary to create a new technology, a vision of a future and the ability to carry out the necessary activities

• There was the research lab to invent new things and a research shop to develop products

• He had an acute sense of marketing

Spring 2006 Harvard Science, A 52 FHA+MBM Lecture 17 14

Edison - continued

• Access to capital to implement the development

• The single mindedness to see the development through

• Few people in our history have combined all of these attributes as well as did Edison

Spring 2006 Harvard Science, A 52 FHA+MBM Lecture 17 15

Now for the Videos

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