Part I.  The Voltmeter


	What is a voltmeter?  Most simply, it is an instrument that is
used to measure the electrical potential between two points,
which is called the voltage.  When you see a voltage listed on a
battery, this indicates how much electrical work can be done with
that battery.  In this lab we will be using 6 volt batteries.

	Let's look at your meter.  Because we are interested in
measuring the voltage of a steady circuit, we will be using the
"DC V" (direct current) scale.  For measuring alternate current,
such as in most residential power supplies, we would use the "AC
V" scale.  The "OHM" scale is for measuring resistance to
electrical flow - the meter applies a voltage to make a circuit
through the material.

	The DC V scale goes from 1000 volts ("1000" on the meter) to
200 millivolts ("200m").  This refers to the amount of voltage
you expect to measure.  For very small amounts you of course
would want to use the smallest scale, millivolts.  The meter
probes have three possible inputs.  The black probe goes in the
"COM" slot - this is the common, or ground lead.  The red probe
plugs into the "V-W-mA", which we use for measuring voltage and
resistance.  The "10A" slot is used for measuring electrical
current, which needs a separate circuit within the meter.

	Turn on the meter to the "20" setting.  On this setting you
can measure voltages as low as 0.01 volts to as high as 99.99
volts. 

1.  Take the black lead and touch it to your battery "-" post,
and the red probe to the "+" post.  What voltage do you
measure?



2.  Check around with other groups.  Does everyone get the same
value?  Why or why not?






3.  Switch the black and red probes on the battery and
re-measure: 



	Whether your voltage is positive or negative depends on your
frame of reference (your probes).  The battery still is providing
the same voltage, it is just your meter's perspective that
changes.  Switch the leads back and continue.

4.  Measure the voltage of your battery while changing meter
scales.  Record your values for each scale.  Which scale gives
you the most information about the battery voltage?

1000 =
200 =
20 =
2000m =
200m =

5.  Put yourself in the circuit:  hold a battery post in one hand
and the meter probe in the other.  What voltage do you measure? 
Why?