each person should have:
1-, 2-, and 4-pack battery holders a multimeter 4 batteries
a light bulb (6.3 volt maximum) bare wire for connections a breadboard
1. Carefully unscrew the bulb from its socket. Make the bare bulb light by using the 2-battery pack. Note in your lab book what connection(s) you had to make to get the bulb to light. Inspect the interior of the bulb socket to see how the appropriate parts of the bulb are connected to the outside metal screws on either side of the socket.
2. Use the multimeter to measure/determine the resistance of the light bulb
a) directly
b) indirectly (using 3 different battery voltages)
Before starting, state your method briefly; all work goes in the lab book. Organize your measured data neatly in a table; leave room for at least three more columns beyond your direct measurements.
3. Explain why your four values for the bulb resistance are different. (Aren't you glad you read Giancoli's section 18(4) in advance?)
4. Cultural literacy: what metal is the light bulb filament made of?
5. Use the resistivity tables in Giancoli and your determined resistance values to calculate the four temperature values of the glowing bulb filament. (Note that you do need the value of room temperature.)
6. Calculate the power of the lit bulb in each case. [Giancoli reading: sections 6(10) and 18(6)]
7. In the Ohm's law discovery lab, you used resistors with values of hundreds or thousands of ohms. Now you should know why. Why didn't we use resistance values smaller than 10 ohms in the Ohm's Law lab?
8. The last goal is to determine how the power (or in everyday terms, "brightness") of the bulb depends on the temperature.
a) On your graphing calculator, plot the bulb power versus temperature (temperature is the independent variable). Do a power-law regression to fit your curve. (This is all the way at the bottom of the CALC Menu under STAT; it's called PwrReg).
b) Notice that this regression fits your data with a y = axb type of curve. Sketch the graph and list the fit parameters (a,b) in your lab book. (And you have, of course, included a translation table.)
c) Use your model to predict how bright a bulb connected to a 12-volt battery should be. (You should not have to use the "a" value in your calculation.) Do not connect a 12-volt (8-pack) to your bulb; it will burn out the bulb.
9. From the results of your investigation, discuss how well your light bulb obeys Ohm's Law.