Check list for debugging one piece of equipment
/ Is there a power light on?/ Does anything change when you turn the knobs?
/ Are the knobs in a foolproof setting ( i.e. the simplest possible setting)?
/ Are the knobs set the same as some similar equipment that is working?
/ If you exchange the item with a working item, do things work better?
/ If you put the suspected item in a working setup, do things still work?
/ Don’t forget, even wires go bad but look good!
/ It still doesn’t work?? Replace it with another if you have spares.
/ If you don’t have spare equipment, you can let the students join another group.
Check list for “None of the equipment in the class works”
/ Did you PRACTICE, PRACTICE, PRACTICE????/ Check for universal cures. e.g. is all the power in the room turned off?
/ Perhaps everyone is following the same bad advice – some student’s, yours, or even the lab manual’s. Rip one of the set ups completely apart and put it back together yourself.
/ The students may not realize how carefully they must follow the instructions to get the experiment to work. Stop everyone and emphasize the importance of following instructions.
/ Nothing has worked yet? Change to a lab on debugging!
/ Still nothing? Change to a lab you can do with some equipment that works.
/ If the concept is really important, change to a two week lab and try, desperately, to get things working by the next week!
/ Change the lab to “extra credit” for the best attempts to make it work.
Check list for “Everything seems to work, but the results are wrong(for the whole class)"
Regard this as not as a problem but as an opportunity to teach about debugging!
/ Point out the virtue of checking the results as you go!/ Ask the class why the results look wrong.
/ Ask the class what could be causing the problem.
/ Do some brainstorming for likely to wildly improbable causes. Almost anything may eventually turn out to be the problem. Be sure to include bad data, bad calculations, and bad theory! Often everyone is copying an incorrect procedure or calculation! See if the class can figure it out.
/ Write calculations out on the board with the help of the class. Beware of mixed units! ( e.g. If one dimension is much larger than another, it is very easy to measure one in meters and the other in mm!)
/ Can you find some stage (from initial measurements to final conclusion) where the data looks ok? If so, you can work toward the end and usually find where things went wrong.
Check list for wrong results for just one group:
/ Congratulate them for checking./ See if the data looks plausible.
/ Examine their NEAT calculations and sketch to see if they were going at it correctly.
/ Still looks ok? Have different members of the group make the measurements.
/ Still won’t work? Have them compare their data with the data of a group that got reasonable results to see if there are any gross differences.
Checklist for common problems:
/ Units/ Math
/ Measuring the wrong thing
/ The instruments were read incorrectly (e.g. oscilloscopes are labeled in volts/interval but the user is supposed to know that it is the large intervals that count, not the small ones!)
/ A “Sanity Check” can eliminate some errors (i.e. having the students measure some known quantity). For voltage measurements, a flashlight battery has about 1.5 volts. If the measurement is 15 volts, there is clearly some error. Varner calipers can measure one centimeter on a meter stick, . . .
/ Instruments may not be set to give calibrated results.
/ The range buttons on instruments may not be understood. Try a sanity check.
/ The students don’t notice or don’t know the meaning of multipliers such as mu (millionth), m (thousandth), etc.