Date: Fri, 16 May 2008 08:22:40 -0500

Light bulbs for CASTLE electricity
COMPILATION. Light bulbs for CASTLE electricity
Date: Fri, 16 May 2008
From: Bill Jameson, DeForest Wisconsin
For reasons of budget, my department has been using Christmas tree light mini-bulbs for our
electricity unit for a couple of years. (So many people throw away strings of lights that we can
get hundreds of free bulbs. We have student lab assistants cut them up and strip the leads to
make them connectable.) Reading the CASTLE materials confirms my recollection that the bulb
holders we chose make the conducting path very visible to the students. However, in order to see
what goes on inside the bulb, the teacher should have a standard light bulb with the glass
removed to show the insides to the students. If I use the mini bulbs taken out of their sockets, the
students will see the two wires that pass into the glass and connect to the filament, and they can
connect directly to those two wires. This makes the conducting path visible to the students.
Pro: There is an easily visible conducting path, and no cost to replace bulbs.
Con: it does not give students experience with screw-base bulbs that most will encounter in
real life; bulbs may not be as uniform in resistance and brightness; I'll have to re-draw a lot of the
pictures for the CASTLE materials.
Date: Sat, 17 May 2008
From: Ben Collman, Juneau, Alaska
We started using Christmas tree bulbs for much the same reason a couple of years ago. (We
also generally do a bit of exploratory stuff with screw-base bulbs.) They can be a bit nonuniform. This can be reduced quite a bit by making sure to use only bulbs from the same string.
After an initial exploratory activity with bare bulbs, batteries and wires, we give them the
Christmas tree bulbs together with AA cells in holders from Jameco electronics. The ones I
bought hold three batteries and have an on/off switch. They have a lid that can be screwed on,
but I left the screws out as it slows changing batteries. I soldered alligator leads to the output
wires, but have had some problems with students breaking off the clips, so probably need to finetune things a bit more.
Date: Sat, 17 May 2008
From: Jim Johnson, Avila University in Kansas City, Missouri
I used Christmas tree lights this year instead of the round bulbs. My students had a habit of
burning them out with either the Genecon, or by connecting one bulb across three cells. (They
are non-science majors getting a science credit.) To approximately match the low resistance of
the round bulbs, I connected two Christmas bulbs (from a string of 100) in parallel to be used as
a single unit. It seemed to work okay. I still have several of the long bulbs (as they seem to be
sturdier against inquisitive kids), and I used them for the items in which it didn't make a
difference which type was used (such as in Unit I); and it had the benefit of preparing the
students for parallel connections in Unit 3. I did tape the two leads from the two Christmas bulbs
together so that they didn't need to make the connection themselves; I told them to think of the
two bulbs as a single item with only two connection points.
Light bulbs for CASTLE electricity
Date: Mon, 19 May 2008
From: Art Zadrozny, Pennsylvania
Re Christmas tree bulbs: ditto in our school; however, I start the unit on circuits having
students construct a circuit using a screw bulb, wire and c-cell battery. I challenge the students
to find up to four different arrangements that work. This helps them realize that a bulb has two
different contact points. (A video I saw [Minds of Our Own, free streaming at]
had 50% of Harvard graduates unable to complete one arrangement! Tell this to your students.)