Some users may need to hit the "reload/refresh" button
to see changes made to this page.
Note: This means that you will need to provide an answer for each of the five different materials used in this lab, each supported by data.
We also want the answers to two additional questions:
These should also be answered (and supported by data) in your abstract and explained in more detail in the Summary of your Argument.
Preparing for the lab:
Answer the pre-lab questions on LON-CAPA after reading the theory information on pages 279 and 280 (as well as in Wolfson section 25.2).
We will be doing the first part of "Lab 28" exactly as described in the lab manual, but will replace the part on series and parallel resistances with a new activity that looks more carefully at some other electrical devices.
This is a pretty straight-forward lab. The main thing you have to be careful about is keeping the power on for very long, particularly with the higher resistance coils. The resistance changes with temperature fast enough to see the voltage change while you are measuring it, which means that you must NOT wait for the voltage to "settle down" to a final value, because it won't. Make your reading as soon as the first few digits of the display are stable. I will remind you of this before the lab.
I will also suggest that you make your measurements for each coil starting with the highest current (1 A) and working your way down. This has two advantages: (a) Most heating takes place at the highest current, so this sequence means that your measurements at lower current will be done with the coil at the same temperature you used for the first one. (b) You can pick the lowest range on the voltmeter that will handle the 1 A case, thus ensuring you get the most significant figures possible in each sequence of voltage measurements. (You should not change voltmeter ranges within a sequence of measurements if at all possible, but can do so between independent sets of measurements.)
This photo shows the equipment the way it may appear when you
arrive. (We may or may not use the Keithley multi-meter as a separate
ammeter in this lab, so it might not be there.)
Please leave it this way when you are done.
In particular, be sure to turn off the multimeter when you are done.
You might also review the information included with a previous lab on how the power supply controls work with particular emphasis on how to select what quantity is regulated and how to adjust the over-voltage limit. You must push the "V" button and change the voltage until it is greater than the highest voltage output we will need in this lab. We usually only need about 9.6 V, so setting it to a 10 V limit usually works well. Once you do that, push the "A" button and set the current to 1.00 A. In this way the power supply will give you whatever voltage is needed (up to 10 V) to produce a 1.00 A current through your resistive load.
Contact me if you have any questions.