1. Lab #1: Ohm’s Law (and not Ohm’s Law) Measure the internal resistance of a battery Study the V vs I characteristics of a diode and show that it does not obey Ohm’s law using a diode, verify Kirchoff’s laws are satisfied even when a non-ohmic device is in the circuit

2. Current Current: amount of charge that passes a point on the wire each second (amps = columb/second) Determined by number of charges and by their speed

3. Basic Electric Concepts Resulting Motion depends on material conductor insulator semi-conductor

4. Basic Electrical Concepts Conductors Terminal velocity depends on voltage, the geometry of the materials, and the properties of the material Resistivity Ohmic materials:

5. Resistance Material resistivity at room temp (  -m) Insulators Mica 2x10 15 Glass 10 12 -10 13 Rubber 10 13 Semi-conductors Silicon 2200 Germanium 0.45 Conductors Carbon 3.5x10 -5 Nichrome 1.2x10 -6 Copper 1.7x10 -8

6. Circuit Symbols

7. Kirchhoff’s Laws What if we have several circuit elements attached together in a circuit?

8. Kirchhoff’s Laws Currents entering junction: + Currents leaving junction: - Loop in direction of current: voltage drops Loop in direction opposite current: voltage increases Where do these come from? voltage has a unique value at a unique place current is just electron moving. Use rules 1 & 2 until you have as many equations as you have variables Label the unknown currents in your circuit

9. Kirchhoff’s Law 3 variables -> need to use rules 3 times

10. Internal Resistance of a Battery Internal resistance of the battery

11. Question: Why not put the ammeter next to R?

12. Fitting and syst errors Suppose you are measuring V using a meter that has infinite accuracy and that has no random errors, but that always reports a voltage that is always off by 0.25V? Chi2 will be zero! Error on slope and intercept will be zero! What to do?

13. slope How can slope be changed? If voltage is always off by a scale factor, or if current is always off by a scale factor, slope is off by the same factor.

14. intercept What if the voltage is always off by a fixed, constant amount? (see “lectures” link of class web site, kelly_SystematicErrors.pdf, for a more complete, rigorous derivation of this result.)

15. Multi-meter syst errors

16. Fitting and Syst Errors Combine this error in quad with the error due to random errors from the linear fitter. If you don’t understand this (how to calculate the syst error on slope/intercept and then combine with the stat error), don’t leave the room today until you do! It’s important for this and future labs!

17. Hints should we record R (the resistance of the variable resistor in your circuit)? For R, should we use the color-band value or should we measure it? big currents! Should we switch to lower scale when using smaller currents? open switch when not in use (try touching the resistors) HOW MANY DATA POINTS? Some of these batteries drift with temperature. Take A.1 and A.5 seriously to avoid this problem. Also, recheck results for first value of resistance used occasionally to look for drift.

18. Lab Starts on page 11 when measure V0 and r, need to report errors on these numbers take at least 5 data points please put text in your spreadsheet, carefully labeling all the data! all numbers should have units! Take A.1 and A.5 seriously! don’t do A.7 (until you take this into account during the linear fit) don’t do C.3 don’t do C.5 Don’t do section VII You must upload your spreadsheet before leaving class!

19. diode How to chose what voltages? Start with the volt meter on the power supply. Slowly dial it from zero volts up, watching the ammeter Don’t dial it above 5 V. Be careful with voltage signs for this one.

20. Bureaucracy Please note lab report is due Feb 8 No class Feb 8