ES Lesson 2: Electrons What are electrons? How to generate electrons for electricity? What is static electricity? © 2012 C. Rightmyer, Licensed under The MIT OSI License, 20 July 2012

Discovery of the atom and its charged particles [ SCIENTIF IC AMERIC AN, Nov 206, 49]

History of element discovery Cobalt (1732) Platinum (1735) 1,000 BC Copper (6000) 2,000 6,0005,0004,0003, ,0000 Gold (5500) Lead (3800) Silver (~4000) Sulfur (~2000) Mercury (1500) Chromium (0) Hydrogen (1500) Zinc (800) Arsenic (1250) AD Antimony (1540) Tin (2000) Iron (4000) Osmium (1803) Palladium (1803) Iridium (1803) Rhodium (1804) Potassium (1807) Rubidium (1861) Thallium (1862) Niobium (1864) Gallium (1875) Indium (1867) Nickel (1751) Bismuth (1753) Molybdenum (1781) Tungsten (1783) Carbon (1789) Tellurium (1795) Oxygen (1771) Nitrogen (1772) Chlorine (1774) Manganese (1774) Sulfur (1777) Yttrium (1840) Uranium (1841) Erbium (1842) Terbium (1842) Tantalum (1844) Sodium (1807) Calcium (1808) Boron (1808) Magnesium (1808) Strontium (1808) Barium (1808) Iodine (1811) Lithium (1817) Cadmium (1817) Selenium (1817) Silicon (1824) Zirconium (1824) Titanium (1825) Aluminum (1825) Beryllium (1828) Thorium (1829) Vanadium (1830) Ruthenium (1844) Ytterbium (1878) Holmium (1878) Thulium (1879) Scandium (1879) Samarium (1879) Caesium (1882) Praseodymium (1885) Neodymium (1885) Helium (1895) Krypton (1898) Gadolinium (1886) Dysprosium (1886) Germanium (1886) Fluorine (1886) Argon (1894) Neon (1898) Actinium (1899) Europium (1901) Lutetium (1901) Polonium (1902 Radium (1902) Lutetium (1906) Rhenium (1908) Radon (1910) Protactinium (1913) Hafnium (1922) Technetium (1937) Francium (1939) Iron smelting Phosphorus (1669) First element isolated chemically First modern listing of 23 known elements (1789) Dalton’s atomic theory (1803) Light spectrum analysis (1901) X-ray spectrum analysis (1922) Mendeleev’s periodic table (1869)

(1803) John Dalton publishes his atomic theory.

(1869) D. Mendeleev publishes his periodic table

Modern version of the periodic table

Here’s an example of three of the 98 natural elements mixed together that make up our air

(1913) Neils Bohr improves the Rutherford atomic model

The hydrogen element’s atom is the smallest of all the elements. Here’s what it would look like if we could see it. Proton Electron

An oxygen atom looks like this. 8 protons 8 neutrons 8 electrons

Water is a chemical compound made by combining hydrogen and oxygen elements (H 2 O) H = hydrogen O = Oxygen

An Electron Generating Machine separates electrons from atoms. Pile of electons. Electrons have a (-) charge. Pile of ions. Ions have a (+) charge. The electrons are strongly attracted to the (+) ions. If a conductor is available, they rapidly flow back to the pile of ions and restore the atom’s neutral charge. Lamps (and other electronic devices) slow the flow of electrons on their return, thereby consuming kinetic energy. Electron Generating Machine (EGM) This machine grabs electrons from atoms and moves them into a pile (as on left). The (+) charged atoms remaining behind are called ions.

[NSTA press, Stop Faking It, W. C. Robertson, 2005] [Teaching Electricity: Yes You Can, Scholastic Professional Books] ES proj 2-1. Use a balloon as a generating machine

ES demo 2-2. Two negatively charged balloons repel one another [Adapted from NSTA press, Stop Faking It, W. C. Robertson, 2005]

ES project 2-3. How to separate salt from pepper using a charged balloon. [Ben Franklin Easy Incredible Experiments, Franklin Institute of Science, Jossey-Bass, 1995]

ES project 2-4. Why does charged tissue paper stick to the wall? [Gateways School, Lewis Camp, 2009 Rubbing the tissue paper with a pencil causes electrons to move from the paper to the pencil. The tissue becomes positively charged. Because the wall is neutral (equal electrons and protons), electrons on the wall move to the surface but are not conducted away. Opposite charges then cause an attractive force that holds the paper to the wall. This is called attraction by induction.

Negatively charged balloon attracts neutral salt and pepper because of induction

How does rubbing cause charging? Before rubbing a plastic rod with wool cloth, both materials have equal numbers of protons and electrons (they are electrically neutral). After rubbing the plastic rod with wool, the wool has less electrons than protons (positively charged) and the rod has more electrons than protons (negatively charged) [Science Action Labs TLC10207 Electricity and Magnetism, Teaching and Learning Co,, Edward Shevick,, 2000] cotton

Adapted from [Science Action Labs TLC10207 Electricity and Magnetism, Teaching and Learning Co,, Edward Shevick,, 2000] ES demo 2-5. Static charge attraction & repulsion rules Two plastic rods rubbed with cotton Two plastic rods rubbed with silk One plastic rod rubbed with silk. Another plastic rod rubbed with cotton. (+) (-) (+) Same charge repels whether positive or negative.Opposite charges attract.

[Intro to College Physics, Appleton-Century-Crofts, R.D. Rusk, 1960] Electric fields between like and unlike charges

Otto von Guericke’s static electric generator (1660)

ES demo 2-6. James Wimshurst’s electrostatic generator (1883) with Peter van Musschenbroek’s Leyden Jar (1745)

ES demo 2-7. Experiments with a motorized rubbing generator as invented by Robert Van de Graff (1929) ions electrons

How far away were the most distant stars viewed by the Hubble telescope in light-years? The “Big Bang” occurred ~ 13.7 billion years ago, and the universe has continued to expand since that time. Hubble, our most capable telescope, can observe stars that are ~ 47 billion light-years away. How far is 47 billion light-years in miles? [ Deep Field]

How to multiply numbers using the decimal powers of 10. Write a number, say Ok, but what does this number represent? (1x10,000) + (2x1000) + (3x100) + (4x10) + (5x1) + (6x0.1) + (7x0.01) + (8x0.001) We know that we can multiply any number by the number 1 without changing the original number. We also know that the ratio (10,000/10,000) is equal to the number 1. The number 10,000 = 10x10x10x10 = 10^4. So, let’s divide the example number by 10,000 and then multiply it by 10^4. The number remains the same, but it is formatted differently: x10^4. What’s really nice about this version of the number is that it makes multiplication really easy. For instance, let’s multiply the example number by another number written in the same format. For instance, let’s multiply by the number 2.0x10^7. ( x10^4) x (2.0x10^7) = x 10^4 x 10^7 = x 10^11 When multiplying factors of 10, all you need do is add the exponents.

Calculate the number of miles equal to 47 billion light years. We know that our sun is 8.3 light minutes or 93 million miles away from earth. So, if we divide 8.3 minutes into the number of minutes in a year, then multiply that number by 93 million miles, we would get the number of miles per light year. –Calculate how many minutes in a year: (60 min/hour) x (24 hours/day) x ( days/year) = = x10^5 minutes per year –Calculate how many miles in a light year: [( x10^5)/(8.3 minutes)] x (93x10^6) = x10^11 ~ 5.88x10^12 miles/light year Finally, calculate how many miles light travels in 47 billion light years: ~ (5.88 x 10 ^12 ) x (47 x 10 ^9 ) = 276 x 10 ^21 miles Written in traditional decimal format, Hubble can “see” 276,000,000,000,000,000,000,000 miles How far can the human eye see into space? ~ 2.6 million light years ( Thus, Hubble can see (47x10^9)/(2.6x10^6) = 18x10^3 = 18,000 times further than the human eye.

Lesson 2 background material

[ Everything is made of atoms

Flying a negatively charged plastic ring Both balloon and ring negatively charged with cotton cloth

[Ben Franklin Easy Incredible Experiments, Franklin Institute of Science, Jossey-Bass, 1995] A home made electroscope Bend 12 guage copper wire Strip of cardboard Hang two flaps made from a 2”x 1/4” of aluminum foil onto the hanger Glass jar Foil flaps open apart when charged (charge can be electrons or ions) Charge eventually bleeds off into air: slowly if air is dry, quickly if moist.

[Intro to College Physics, Appleton-Century-Crofts, R.D. Rusk, 1960]

Distribution of positive charge on variously shaped metal conductors [Intro to College Physics, Appleton-Century-Crofts, R.D. Rusk, 1960]

Electric field density highly magnified for a pointy object such as a sharpened metal rod