Here are some things to do to finish this section.
What question did you think of that could be studied, or
observation could you make that is interesting or unexpected?
Send it to the Question board!
Discuss these questions with the people in your group. Please
send us a discussion of two of these
questions. Don't forget to tell us the group name.
You can buy light bulbs intended for 115 V with a wide range of
wattages -- 5 W for little nightlights up to 250 W and more for
lights intended to illuminate the whole back yard. Which kind uses
the most current? Which kind has the highest electrical
resistance?
Is it safe to combine ordinary 115 V light bulbs with the
materials in the kit? What would happen if we connect a 40 W light
bulb from the grocery store to a battery?
You are shopping for a new light bulb for your desk lamp, and
the salesperson offers you the choice between a 100 W incandescent
bulb and a 25 W compact fluorescent bulb. Is it good or bad that
the wattage of the compact fluorescent is smaller? The salesperson
is correct in claiming
that they are equally good for lighting -- how can this be true?
To really compare the two, we should note that the compact
fluorescent bulb costs $5, while the incandescent bulb only costs
$1; they both are expected to give light for 10,000 hours. Does
this difference in initial cost matter very much to the
decision?
In your kit you will find a small piece of thermal sensing sheet.
It is a kind of thermometer, that is probably black at room
temperature but will turn green or blue when you
touch it (or if it is rather warm in the room). When you are
through playing with it, let it cool back to a uniform color.
Meanwhile, cut a piece of aluminum foil that is 1/2 cm wide and 10
cm long. Straight is OK, but it is more fun if it is somewhat
curvey. We are going to use this as a wire. Place the thermal
sensing sheet on top of the aluminum foil wire, so that the two
ends of the foil stick out. Attach wires with clip ends to the
battery, and then to the ends of the aluminum foil, to make the
circuit diagrammed at left. Explain what happens.
Notice that what we have made here is an example of the circuit
(sometimes called "a
short circuit"), which you were warned not to make. What's wrong
with a short circuit?
If there is something that you don't understand about voltage and
resistance, Ask us!
This is the end of this unit. (Check this
box ) The next section is about circuits
(sometimes called "a
short circuit"), which you were warned not to make. What's wrong
with a short circuit?