Re: Writing a Physics Lab

[Arlyn DeBruyckere <arlynd@HUTCH.K12.MN.US>]

Tina,
    I just had my high school students do this lab on Monday.  Since we
are just ending the 4th week of physics they still need some guidance but
I require THEM to write the lab.  I start by reminding them that in
previous labs we have done measurements where we made the assumption that
the connecting wires had no resistance but those that used low resistance
in their circuits noticed large errors that are caused by the resistance
of the connecting wire.  A couple of students even came up with a new
name for this lab that I think I will use in the future "IRresistible!"
I tell them the purpose of the experiment is to determine the factors
that will predict the resistance of wires.  To do this they will need to
set up a circuit to measure the "usual" properties of a circuit of
potential difference and current so they can measure the resistance.
They will need to set up a table with these quantities along with another
column for any other quantity they think might be related to the
resistance of the wire.  I tell them to protect the wires and the meters
in the circuit the power supply should initially be set to less than 3
volts and to have the circuit on for only about 20 to 30 seconds or the
wires will get very hot.  I have the same types of "boards" as well as
many very old spools and some new spools of different kinds of wire.
These individual spools don't provide the nice regular pattern that the
preset board does.  This is a great experiment in testing and improving
student's ability to control variables.  They not only have to recognize
that the size, length and kind of wire are variables in the resistance
but they must also change only one at a time to determine the effect of
each.  My students can't all do this but the majority can, on their own,
determine that the resistance is directly proportional to the length,
that the kind of material the wire is made from causes differences in
resistance and that the "thicker" the wire the less resistance it has.  I
then take the time to show them a American Wire Gauge chart so they can
relate the "thickness" of the wire to AWG and area.  If you don't have
ready access to this chart I've got it on a .pdf file and in Appleworks.
I can also convert it to Word if you'd like.  We then discuss the
importance of having the "correct" extension cords at home to run
appliances and the dangers of overloading a wire.

    I believe that because THEY have to write up the experiment and
control the variables, they remember the results better and they also
start learning how to control variables in a true experiment.

Tina Fanetti wrote:

> Okay
> I have this piece of equipment.  Its a board with a bunch of wire wra=
> pped around a wooden stick.  Each coil of wire is a different length,=
>  thickness or material.  I believe the purpose of this board is to sh=
> ow how resistance depends on resistivity of the material, length and =
> cross-sectional area.
>
> Thanks
> tina

--
Arlyn DeBruyckere
Science Teacher
Hutchinson High School
1200 Roberts Road
Hutchinson, MN 55350
320-587-2151
mailto:arlynd@hutch.k12.mn.us
http://www.hutch.k12.mn.us
http://www.hutch.k12.mn.us/teacher/ArlynDeBruyckereHS.cfm