Download Electricity Lab (Teachers Edition)

Name: ________________________________
Per: _______ Date: ___________________
Electrical Resistance Lab (Teacher’s Edition)
Question for this Investigation:
Do all objects conduct electricity equally well?
Materials:
 6-10 wires with “alligator” clips on ends
 2 battery holders
 3 light bulbs in holders
 2 knife switches
 3 resistors of different “R” values
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2 “D” batteries
Digital Multimeter
A wooden pencil, sharpened on
both ends
Pieces of foil, wood, plastic, other
random items
Procedure:
1. Which objects do not let electricity flow?
As you know from life experience, different materials let electricity flow well and others do
not. The materials that do are called conductors. Materials that hinder current flow are
called insulators. With the different objects that were given to you by your teacher, design
an experiment to test whether each object is a conductor or insulator. Put your observations
in the table below.
Object Description
Steel Nail
Prediction: Conductor or Insulator?
Whatever
Observation: Conductor or Insulator?
Conductor
Wood
Whatever
Insulator
Aluminum foil
Whatever
Conductor
Graphite in pencil
Whatever
Conductor
Questions!
1. What was the procedure that your group followed to test these materials? Write
this down in step form below (Step 1: Make a …, Step 2: Take a …, etc.)
1. Made an electric circuit using a battery, a light bulb, and some
wires.
2. We completed the circuit to make sure the light bulb lit up and
then we broke the circuit at the wires.
3. Next, we took each object and on opposite ends, placed the
loose ends of the wires.
4. Then we observed whether or not the light bulb lit up again. If it
did, the object was a conductor, if it didn’t, it was an insulator.
2. What are some similarities between the conductors? The insulators?
The conductors all were metal and the insulators weren’t.
3. If an object’s “resistance” is its ability to withstand electric current flow, which
objects have higher resistance?
Insulators have higher
resistance.
2. Measuring Resistance
Resistance is a measurable quantity and is
measured in ohms (Ω). Set the digital
multimeter to “Ω”. This will allow it to
measure an object’s resistance. Connect the
two leads to various items and look at the
resistance amounts they give. Record this in
the following table.
Object Description
Steel Nail
Resistance (Ω)
0
Wood
1 (infinite)
Aluminum foil
0
Graphite in pencil
0
Question!
1. What relationship did you notice between the resistance and whether a material was a
conductor or insulator?
The conductors all had a resistance of 0 Ω, but the insulator had a reading
of infinite resistance.
3. Mystery Resistors
Your group should have 3 resistors that all have different amounts of resistance. You need
to figure out their resistances however you are not allowed to use the method we just learned in
step 2. There is another way called Ohm’s Law. With Ohm’s Law, if you know the voltage and
current passing through a resistor, you can calculate its resistance!
Ohm’s Law
V=IxR
Once again, your group will need to design a method for figuring out the resistance of each resistor
using Ohm’s Law. Write Show your work below the table, write your data in the table, and
remember the steps of your procedure. (Hints: Remember how we measured voltage and current in
the last lab. Be careful of your units for current.)
Resistor color
Blue
Battery voltage (V)
2.8
Current (A)
.08
Resistance (Ω)
35
Red
2.8
.14
20
Green
2.8
.28
10
Show work here:
R=V/I
R = 2.8 V / .08 A = 35 Ω
Questions!
1. What was the procedure that your group followed to test these materials? Write
this down in step form below (Step 1: Make a …, Step 2: Take a …, etc.)
1. We made a circuit with a battery, a switch, some wires, and a
mystery resistor. They were all lined up so there was only one
path around.
2. We opened the switch and tested the current using the
multimeter.
3. Then we closed the switch and used the multimeter to test the
voltage across the resistor.
4. Knowing the voltage and current, we used Ohm’s Law to
calculate the resistance of the resistor.
5. We redid steps 2 – 4 for each of the mystery resistors.
2. Test the resistances directly using the multimeter. Were your calculations
correct? If they were a little off why do you think that was? (Think hard, this is
part of your error analysis.)
The resistances were a little different when we tested the objects
directly with the multimeter. However, our calculations were
basically correct. They could have been off due to inaccuracy in the
multimeter, slight internal resistance in the multimeter, or some
human error in the measuring. The resistances were Rblue = 33.1 Ω,
Rred = 19.4 Ω, and Rgreen = 9.6 Ω
Conclusions
1. What is the difference between conductors and insulators?
Conductors allow current to flow easily through themselves.
Insulators do not.
2. Think of at least two uses in your everyday life for conductors and then two for
insulators.
Conductors – wires to my TV, metal plug connectors to outlets, car
jumper cables, etc.
Insulators – shielding around wires and cables, rubber grips on tools,
air around an exposed wire