Getting to Know Your
Multimeter
Materials:
Multimeter
with 2 probes (one black, the other red)
200
in 1 Electronic Project Lab circuit board
Genco
Hand Crank DC Generator
Battery(s)
(at least 3 AA’s and one 9Volt)
Key Formulas and Ideas to be aware of:
V =
IR
V =
Voltage measured in Volts
I =
Current (amount of charge (Q) passing a point in time (t)). Measured in Amps = Q/t
R =
Resistance measured in Ohms (symbol: W)
If
you hook up a battery to a system, the battery acts as a pump and continuously
pumps the voltage rated on the side of the battery. Eg. A 12 V battery will
always produce 12 Volts
A
resistor will continue to resist the current at the same rate as well. Except, as it gets hotter, many resistors
will INCREASE their resistance. But, if
we say that something obeys "Ohm’s Law”, we are saying that the resistor
is maintaining a constant value.
Warning: Never ever hook up a multimeter which
has its dial set to the resistance setting (W) and a LIVE
circuit (one with a battery hooked up to it). WHY? Because this
setting has your multimeter sending out a current from the 9.0 Volt battery from
inside the multimeter to test the resistance of a resistor. You
will wreck the multimeter if you also send a current through the circuit from
another source (such as another battery outside of the multimeter). This
setting is to test a resistor which has no current flowing through it.
Pre-Lab Questions: Type answers in space provided in RED type.
Look at the equation V = IR.
1. What happens to I if V is increased and R
stays the same? ____________
2. What happens to I if R is increased and V
stays the same? ____________
3. What happens to V if R is increased and I
stays the same? ____________
4. What happens to V if I is increased and R
stays the same? ____________
5. What happens to R if V is increased but I
stays the same? ____________
6. What happens to R if I is increased but V stays the same?
____________
7. What is the slope of a V vs. R Graph equal
to? ____________
8. What is the slope of a V vs. I Graph equal
to? ____________
9. What should you never ever do with your
multimeter (see above warning)
Instructions: Fill in the blanks with numerical values. Be sure to include Positive and Negative
signs. Type answers in space provided in
RED type.
Voltage:
-Turn
Multimeter Dial to 20V
-Connect
Black probe to COM (COM stands for “common” or ground)
-Connect
Red probe to W/V
1. Touch the black probe to the – side of the
battery and the red probe to the + side of the battery. What does the multimeter read? (include positive or negative)
_______________________V
2. Switch the probes so the red is touching
negative, and the black is touching positive.
What
does the multimeter read? (include
positive or negative)
_______________________V
3. Hold 2 or 3 batteries in SERIES (or if you
have a battery “pack” where you can put two or more batteries in there, use
that).
How
many batteries (and what type, AA, D, C?…etc) did you put in series _______
What
did the multimeter read? __________
Add
up the voltages on the sides of the batteries and put that value here _________
4. Predict the voltage of 4 AA batteries in
series (each AA has 1.5V) ___________
Voltage Part II:
-Hook
up the multimeter probes to the hand-crank Genco Generator. It doesn’t matter which probe gets which
alligator clip from the Genco Generator.
-Set
the multimeter for 20 volts
1. Crank the generator clockwise. Are the voltage readings you are getting
positive or negative? ________________
2. Crank the generator counter-clockwise. Are the voltage readings you are getting
positive or negative? ___________________________
3. Switch the alligator clips so that the one
on the red goes to the black (and vice-versa).
Now crank the generator clockwise.
Are the voltage readings positive or negative? ________________
4. Based on your observations from the previous
3 questions, would you say that the generator provides AC or DC? ________________________
5. How do you change the direction of current
flow with the hand-crank generator?
________________
Resistance (ohms or W):
-Keep
red and black probes connected to multimeter as you did for Voltage
-Turn
multimeter dial to 20MW
-Make
a dark line of PENCIL on a sheet of paper.
Thick dark line, about 2 cm wide and maybe 5-6 cm long.
1. Hold one probe on one extreme of the pencil
mark and the other probe on the other extreme.
What does the multimeter read?
________________
2. Bring the probes closer together along the
pencil line. What does it read? ________
3. Bring them closer still ________________
4. Touch the probes together, what does it
read? ______________
WHY? Because: The multimeter sends out a voltage (9V
because it is a 9V battery in its battery pack). The carbon in the pencil “lead” resists the flow of electrons
being pushed by the 9V battery. The
greater the distance between your probes, the greater the amount of carbon the
electrons can be resisted. Touch the
two probes together and there is no resistance – the multimeter should register
ZERO!
NEVER EVER HAVE A RESISTOR POWERED BY A
BATTERY AT THE SAME TIME YOU ARE USING A MULTIMETER TO TEST IT. WHY? BECAUSE THE MULTIMETER IS GIVING IT SOME
VOLTAGE AND SO WOULD YOUR BATTERY. NOT
ONLY WOULD THIS GIVE YOU A FALSE READING ON YOUR MULTIMETER, BUT IT MIGHT ALSO
CAUSE THE RESISTOR TO BURN OUT IF IT GETS TOO HOT
Resistance Part II:
-Set
the multimeter to 200W
-Get
out the 200 in 1 Project Kit
-Touch
the probes to the springs across a 100W resistor (Spring #1 and
Spring #2)
1. What does the multimeter read (include + or
– sign) _____________
2. Switch the black and the red probes so that
they are now touching the other spring.
What does the multimeter read (include + or – sign) _____________
3. Use V = IR and the fact that the multimeter
has a 9V battery in it to help you figure out what current (I) must be flowing
through that resistor ____________
4. Set the multimeter to 2K and touch the
springs across a 1KW resistor (springs #13 and
#14) What does it
read?___________________
Resistance Part III:
-Set
your multimeter dial to 2KW
-Wire
your 200 in 1 kit as follows: Wire
spring #1 to spring #3. In future, I
will write a wiring instruction like this as:
1-3. That means put a wire in #1
and connect it to #3.
1. Put the red probe into #2 and the black
probe into #4. What does the multimeter
read? _____________
2. Did you wire these two resistors in SERIES
or PARALLEL? ___________
3. Use the equation: Rseries = R1 + R2….etc to determine the total
resistance __________ I hope this matches your answer to #1.
-Set
your multimeter dial to 200W
-Wire
your 200 in 1 kit as follows: 1-3 and
2-4
1. Put the red probe into #1 and the black
probe into #2. What does the multimeter
read? _____________
2. Did you wire these two resistors in SERIES
or PARALLEL? ___________
3. Use the equation Rparallel =
1/(1/R1 + 1/R2) to determine total Resistance
___________ I hope this matches your
answer to #1.
4. ON A SEPARATE SHEET OF PAPER – NOT HERE ON THE COMPUTER: Draw a schematic diagram of your resistor set-up.
5. Put Red probe in #3 and the Black probe in
#4. What does it read? _________
6. Try Red in #3 and Black in #2. What does it read? ________
7. Try Red in #1 and Black in #4 ________________
8. Try Red in #2 and Black in #4 _______________
9. Try Red in #1 and Black in #3 _______________
10. Why do you get a lower reading in Question
#8 and #9? ___________________________________________________________________
11. Hold Red in #3 and Black in #1. Turn the dial to 2KW.
Pull out the wire which connects 1-3.
Does the multimeter now read the same as when these two resistors were
in SERIES? Yes or no _______________
12. Why is it not in SERIES with the wire still
connected to 1-3? Refer to the drawing
you made on your paper to help you explain this.
Current (amps or Charge/time
or Q/t):
-Plug
the red probe into the 10A part of the multimeter
-Keep
the black probe in the COM
-Set
the dial on the multimeter to 10A
-Hook
up your 200 in 1 kit as follows: Use a wire
to connect the following numbers
60-1
58-into the air (don’t hook 58 up to
anything; just leave its wire hanging out of the box)
1. Hold the red probe tip into #2 on the 200 in
1 kit board. Hold the black probe tip
to the wire leading out of #58. What
does the multimeter read? _____________
2. Now connect 58-1 and leave 60 hanging out of
the box. Again, hold Red in #2 and hold
black on the wire hanging from #60.
What does the multimeter read?
________
3. Use V = IR to confirm what you just saw: The batteries you hooked up had a total voltage ot 4.5V and the resistor is 100W. Your Current should be 4.5V/100W = 0.045 amps. Is that what you got for questions 1 and 2? ____________
Why? Because:
Current flows through a circuit and in order for the multimeter to read
the amount of current, it must be in SERIES with the circuit. Can you see where the circuit is broken so
that you could insert the red and the black probes?
-Plug
the red probe into the W/V part of the multimeter
again.
-Hook
up the 200 in 1 kit as follows: 60-1
and 58-2
-Turn
the dial of the multimeter to 20V
1. Hold the red probe in #1 and the black probe
in #2. What does the multimeter
read? ____________VOLTS
2. In this arrangement, are your probes in
SERIES or PARALLEL with the circuit?
_________
3. Fill in the blanks with SERIES or
PARALLEL: Ammeters must be in
____________ with the circuit, while Voltmeters must be in ______________
Current part II:
-Hook
up your 200 in 1 kit as follows: 1-3, 60-4
and 58 – air.
-Make
sure your multimeter is set to 10A on the dial and the red probe is back in the
10A hole on the face of the multimeter.
1. What is the total resistance of this
series? You can look at your answer
from Resistors III if you want to or you can re-do the math (Rseries
= R1 + R2) ______________
2. Use V = IR to predict the I for this
one. The V = 4.5 volts – can you see
why? What is the Current you should
read on the multimeter? _________________
3. Hook the red probe into #2 and the black
probe to the bare wire coming out of 58.
What does it read?
______________(was your prediction correct?)
4. Now wire it up like you did for the PARALLEL
resistors in Resistance part III.
What was the total resistance of the PARALLEL resistors? You can look at your answer from resistors
part III if you want to
_________________
5.
Use V = IR to predict the I for this one.
The V = 4.5 volts – can you see why?
What is the Current you should read on the multimeter? _________________
6. Hook
the red probe into #1 and the black probe to the bare wire coming out of
58. What does it read? ______________(was your prediction correct?)
7. Hook Red probe into #2. What does it read?_________________
8. Hook Red probe into #3. What does it read? _________
9. Hook Red probe into #4. What does it read? ____________
10. Why is this
happening? ON A SEPARATE PAPER, DRAW A
SCHEMATIC OF THIS AND EXPLAIN IT HERE
_________________________________________________________________
Current part III:
-Plug
the red probe into the 10A part of the multimeter
-Keep
the black probe in the COM
-Set
the dial on the multimeter to 10A
-Have
3 batteries at the ready.
1. Hook up the red probe to the positive
terminal of one battery and the black to the negative terminal. What does it read?______________ (call this
battery #1)
2. Do this for the second battery (by
itself). What does it read? ____________ (call this battery #2)
3. Do this for the third battery (by
itself). What does it read? _________ (call this battery #3)
4. Now put battery #1 and battery #2 in series
and test the current from the positive terminal of the top battery to the
negative terminal of the second battery.
What does it read?___________amps
5. Now put battery #2 in series with battery #3 _________amps
6. Now put battery #1 in series with battery
#3 ________amps
7. Now put battery #1, #2 and #3 in series _______amps.
Essentially,
what you are doing when you do this is you are creating a “dead short” in the
battery so that the battery is forced to give you all of its possible current
outflow at once. Remember that if you
have a low resistance, current is high. All you have in the way between the positive and negative
terminal of the battery is a wire (very low resistance).
With this information you can determine
the minimum resistance you could hook up to these batteries and get the current
that resistor needs (V/I = Rminimum)
8. What is the lowest resistor you could hook
up to battery #1?__________ohms.
9. What is the lowest resistor you could hook
up to battery #2?__________ohms.
10. What is the lowest resistor you could hook
up to battery #3?__________ohms.
What
generalization can be made about hooking up batteries in series which have
different maximum current outputs? Look
at your answers to 1-7. Is the current
output from a series of #1, #2 and #3 the sum of their individual currents in a
dead short? Is it the average? Is it the lowest one?
____________________________________________
Now
I want you to create some circuits and show me that you know what is going
on. Make your numerical predictions
first, then set the whole thing up, then call me over to show me that you are a
genius!
1. Create a circuit with at least two resistors
in series and put those two in parallel with another two resistors in series
(in other words, 4 resistors in all. 2
in series with each other, and another 2 in series with each other, but the two
sets are PARALLEL to each other.
Answer
the following:
a. Predict the Voltage across each of the 4
resistors
Resistor
1 ______________
Resistor
3 _____________
Resistor
4 ______________
b. Test the Voltage across each of the 4
resistors and show
Mr. Young that it matches your predictions
c. Predict the Current (I) flowing through each
of the 4 resistors and the total resistance.
Resistor
1 ______________
Resistor
2 _____________
Resistancetotal____________________
d. Test the Current across each of the 4
resistors and show
Mr. Young that it matches your predictions
e. ON A SEPARATE PAPER, DRAW A SCHEMATIC OF YOUR SET-UP.
What is due for this lab?
1. Answer everything you see from the PRE-LAB
on down to the bottom of this lab wherever you see a blank line. Be sure your answers are in RED. Turn in this whole document as a file with
your initials followed by the word “multimeter”. (gymultimeter.doc) Be sure to put the names of all of your
group members at the top of the lab!
2. On a separate sheet of paper, with each one labeled as to which one it is, draw the schematics for: (or, if you want to impress me – scan them into your document!!!!!)
·
Resistance III #4
·
Current II #10
·
Show and Tell Time #1e
You can write any explanations for these schematics
on your electronic version you turn in (you know, in RED)