1. BE Lesson 2: Resistance What is conductance? What are resistors? What is Ohms law? What is a Watt? © 2012 C. Rightmyer, Licensed under The MIT OSI License, 20 July 2012

2. Pure silicon atoms are good insulators Adapted from Getting Started in Electronics, Master Publishing, Inc., Forrest M. Mims III, 2010

3. Copper atoms are good conductors Copper, a metallic material, happens to be an excellent electrical conductor. It has 29 protons and 29 electrons. The electrons are in 4 distinct orbital orbit locations called “shells”. Note that the highest shell contains a single electron. This electron is located far away from the nucleus, and is therefore weakly attached to the atom’s charged particle structure.

4. BE project 2-1. Take apart a shop light and see how it works ES proj 4-3

5. BE project 2-2. Use a multimeter to measure resistance ES proj 4-4

6. What are insulators? Insulators are materials that greatly resist the flow of electrons. Here are some examples: glassrubber oilasphalt fiberglassporcelain ceramic quartz (dry) cotton(dry) paper (dry) woodplastic airdiamond pure water

7. Is air really a poor conductor?

8. What are the electrical components called resistors? Resistors are electrical components very often used in electrical circuits to control the amount of current. Resistor are available in a large range of values and are typically made using these types of materials: Resistive metal film Resistive wire Carbon film Carbon composition Metal oxides Cement This is the electrical symbol for a resistor. Its resistance value, R, is measured in ohms.

9. Smaller resistors are 1/8 watt; larger is 1/4 watt Brown = 1% Red = 2% Gold = 5% Silver = 10% Examples: 1 = Brown-Black-Gold 10 = Brown-Black-Black 100 = Brown-Black-Brown 1000 = Brown-Black-Red 10,000 = Brown-Black-Orange Note exeception How do we read the ohm value (  ) of older resistors? Wide gap * Note: some resistors have a third digit before the multiplier.

10. How do we read the ohm value (  ) newer resistors? Adapted from Vellerman K4001 kit assembly manual. www.vellerman-kit.com

11. BE project 2-3. Measure resistor Ohm values (  ) ES demo 4-5

12. How to use a wire stripper. Electric Circuits for Grades 3-6, Lawrence Hall of Science, University of California Berkeley, LHS GEMS, 2004

13. BE project 2-4. Make a battery connector ES proj 4-1

14. Typical breadboard with an X-ray vision of the copper strips on the back of the board Adapted from Make: Electronics, Oreily Media Inc, Charles Platt, Dec 2009

15. Breadboard orientation

16. BE ckt 2-5. Circuit to learn about the plug in breadboard + 9.0 volts 330  + Long lead of LED oriented towards top LED ES ckt 4-6

17. (1827) George Simon Ohm develops Ohm’s Law Voltage = (current) x (resistance) http://www-history.mcs.st-and.ac.uk/Biographies/Ohm.html

18. Ohm’s Law Ohm’s law states: V = I R where V is voltage (measured in volts), I is current (measured in Amps) R is resistance (measured in Ohms) This equation can be restated as I = V/R, or R = V/I

19. Use Ohm’s law to calculate current in this circuit + - V = 9.0 v I = ? R = 1000 ohms To calculate the current, divide the voltage drop across the resistor by the resistor’s ohm value. For instance I = V/R = (9.0/1000) = (0.009 amps) = 9 ma. To calculate the voltage drop across the resistor, multiply the current by the ohms. For instance V = IR = (0.009 x 1000) = (9.0 v). To calculate resistance, divide the voltage across the resistor by the current. For instance R = V/I = (9.0/0.009) = 1000 ohms

20. BE ckt 2-6. Learn about Ohm’s law (step 1) + 9.0 volts ES ckt 4-7

21. BE ckt 2-6. Ohm’s law hookup (step 2) + ma 9.0 volts Digital multimeter set to measure 200 mA

22. BE ckt 2-6. Ohm’s law hookup (step 3) 1000 ohm = Brown-Black-Red = 1K ohm + ma 9.0 volts 1K Digital multimeter set to measure 200 mA

23. BE ckt 2-6. Ohm’s law hookup (step 4) + ma 9.0 volts vdc Second digital multimeter set to measure 20 volts DC 1000 ohm = Brown-Black-Red = 1K ohm 1K

24. Measure the voltage drop across one of the two series resistors (BE ckt 2-7) I = 9.0/(1000+1000) = 9.0/(2000) = 0.0045 amps =4.5 milliamps = 4.5 ma. V R = I x R = (4.5 ma) x (1000 ohms) = 4.5 volts + - V = 9.0 v I = ? R = 1000 ohms DC Amps VOM: ma 4.5 v

25. + ma 9.0 volts vdc Second digital multimeter set to measure 20 volts DC 1000 ohm = Brown-Black-Red = 1K ohm 1K Same as circuit 2-2 except for addition of a second 1K resistor. BE ckt 2-7. Learn about resistors in series 1K ES ckt 4-8

26. What happens if we add a second resistor in parallel? (BE ckt 2-8) I = (9.0/1000) + (9.0/1000)= (0.009 + 0.009) = 0.018 amps = 18 milliamps = 18 ma + - V = 9.0 v I = ? DC Amps VOM: ma 1000 9.0 v

27. BE ckt 2-8. Learn about resistors in parallel Expected current through two parallel 1000 ohms resistors = ~ 18 ma. + vdc ma 9.0 volts 1K ES ckt 4-9

28. BE project 2-9. Investigate characteristics potentiometer (pot) -- a variable resistor [Walch Hands-on Science Series: Electricity and Magnetism, Weston Walch Publisher, 2000] ES demo 4-10

29. Light Emitting Diode (LED) Adapted from http://www.kpsec.freeuk.com/components/diode.htm

30. Symbol for LED BE ckt 2-10. Measure the voltage and current required to turn on an LED. LED ma Notes: (1) LED’s require about 1.5 to 1.7 volts to begin operation. (2) Brightly lit LEDs consume about 12 milliamps. + - 50k pot 9 v + vdc

31. Hookup diagram for BE ckt 2-10 Longer lead of LED goes to the top (+). Expected about 1.8 volts and 5 to 8 ma for bright LED operation. 50K  pot + 9.0 volts ES demo 3-5 ma vdc LED

32. Watts = Volts * Amps + - VOM DC Amps + - VOM DC Volts + -

33. Energy consumption examples measured in Watts Oscilloscope (50 watts) HiFi Amplifier (200 watts) Space heater (1500 watts)

34. A “smart” meter reading kWh power consumption