Resistance
Using the Resistor Color Code
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What are Resistors?
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Resistors are important because they are control
devices for electronics.
Resistors can be physical devices.
Resistance can also be a physical characteristic of
a circuit or component.
Resistors allow a circuit to deliver exactly the
right amount of current, voltage, or power to a
circuit or device (and no more).
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What is Resistance?
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Resistance is defined as the opposition to current
flow.
The primary purpose of a resistor is to control
current.
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By control we mean limit or adjust
A resistor is a linear device (unlike some other
circuit components that are not linear)
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Like diodes and transistors
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Fixed vs. Variable
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Fixed resistors are designed to have a nearly
constant amount of resistance regardless of
voltage, current, age, heat, or time.
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They have a stable value within a tolerance.
The narrower the tolerance, the more expensive
Variable resistors can change resistance value.
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They are adjustable.
Examples: potentiometers and rheostats
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Symbols and Characteristics
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Resistor schematic symbols are used to represent
a variety of circuit components with resistance.
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The schematic symbol is a zigzag line.
Real resistors look like a tube or a cylinder.
A resistor is often called a load on a circuit.
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More Resistor Characteristics
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Another important characteristic is the power
rating.
A power rating is related to physical size.
The resistance value has nothing to do with
physical size.
Resistance is often related to a concept like
friction, but they are not exactly the same.
Resistance is useful.
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Types of Resistors
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Fixed
Symbol:
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Types of Resistors
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Variable
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Potentiometer
Rheostat
Tapped
Symbol:
Source: http://crazy.pcmscs.org/physics/induction/Photos/gif/r_var.gif
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Measurement and Symbol
Resistance is measured in
Ohms
Symbol for resistance is
 (Greek symbol Omega)
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Resistor Color Code Chart
Source: http://www.argyll.epsb.ca/jreed/jhscience/graphics/col_code.gif
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Memory Aid (mnemonic)
Black (0)
Brown (1)
Red (2)
Orange (3)
Yellow (4)
Green (5)
Blue (6)
Violet (7)
Grey (8)
White (9)
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Memory Aid (mnemonic)
Black (0) = Big
Brown (1) = Boys
Red (2) = Race
Orange (3) = Our
Yellow (4) = Young
Green (5) = Girls
Blue (6) = But
Violet (7) = Violet
Grey (8) = Generally
White (9) = Wins
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Memory Aid (mnemonic)
 Big
Boys Race Our Young Girls But
Violet Generally Wins
 0,
1, 2, 3, 4, 5, 6, 7, 8, 9
 Remember,
it starts with zero
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Identifying the Bands
Notice this gap between the
3rd and 4th color band.
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Identifying the Bands
One band can also be closer
to the end on one side. This
is the first band.
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Identifying the Bands
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Here is a picture showing the color bands starting
closer to one end.
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Identifying the Bands
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Here is a resistor showing the gap between
bands.
In this picture it is hard to see which
band is closer to the end, but the gap
is easy to see.
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Reading the Resistor Value
From the Color Bands
These three bands identify the
resistor value.
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Reading the Resistor Value From
the Color Bands
The 4th band indicates
the tolerance range.
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Example
First Band: Yellow
Big Boys Race Our Young
0, 1, 2, 3, 4
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Example
First Band: Yellow
equals 4.
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Example
Second Band: Violet
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Example
Second Band: Violet
equals 7.
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Example
Third Band: Brown
equals 1.
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Example
Third Band: is the multiplier
equals a single zero
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Example
Fourth Band: Gold
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Example
Fourth Band: Gold
This is the tolerance band.
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Example
Gold equals a tolerance
of five percent.
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Example
So this resistor has a value of
470 Ω with five percent tolerance.
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Example
This resistor should have a
measured value between
446.5 Ω and 493.5 Ω.
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Determine the value of the
following resistor.
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Determine the value of the
following resistor.
Brown, Black, Red, Gold
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Determine the value of the
following resistor.
Brown, Black, Red, Gold
1
0
2 5 percent
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Determine the value of the
following resistor.
Equals 1000 Ω, plus or minus 5 percent
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Determine the value of the
following resistor.
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Determine the value of the
following resistor.
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More practice:
Determine the value of these
actual resistors.
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Resistor Tolerance
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Resistor tolerance is a range of resistance values
where the resistor is still OK.
Resistor values have a range because they can
change with age, current, or temperature.
The range is plus or minus from the indicated
value.
Often, the resistance value does not have to be
exact.
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Resistor Tolerance
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Use the indicated value of the resistor to
determine tolerance.
Multiply the indicated value times the tolerance.
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Add and subtract the tolerance from the indicated
value.
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Example: 5 percent of 1000 is .05 X 1000 = 50
Example: 1000 – 50 = 950, 1000 + 50 = 1050
The acceptable range of resistance is
950 Ω to 1050 Ω.
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Resistor Measurement
 Read
resistor value from color code.
Measure the resistor value with a
multimeter.
 Compare indicated value to measured
value.
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Check it Out
To measure resistance value:
1. Plug the red (positive) lead into the V
(Voltage/Resistance) connection hole.
2. Plug the black (negative) lead into the COM
(Common) connection hole.
3. Turn the measurement range dial into the
resistance settings area.
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Check it Out
4. Set the range setting to a level higher than the
resistance of the resistor you will be measuring.
5. Touch the red lead to one end of the resistor
and the black lead to the other end.
6. The readout will display the resistance value
according to the scale you set.
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Check it Out
Record your actual measured resistance value
for the resistor and the corresponding “color
bands” on the resistor in the table
in your Lab Journal.
Resistor
Actual
measurement
8. Set these resistors
aside, they will be
470
used later.
1.0K
9. Turn the measurement
1.5K
dial back to OFF when
1.0M
not in use to conserve
the battery.
7.
Color
bands
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Make the Connection
1. Use your multimeter to measure the resistance of your
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body from one hand to the other.
Set the meter to 20M.
Grab the tip of the red lead between two fingers in
your right hand.
Grab the tip of the black lead between two fingers in
your left hand.
Squeeze tightly, and note the resistance measurement
on the readout.
Record your measurement.
 What factors do you think cause the variations
between the measurements of various people?
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Make the Connection
Now lick the four fingers you used to get them wet and
repeat the measurement.
8. Record the new measurement.
 Does your body conduct electricity?
 How did licking your fingers affect the
measurement?
 Compare your measurements with others. How do
the measurements vary?
 What factors do you think cause the variations
between the measurements of various people?
7.
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Resistor Size vs. Value
Notice that
resistors come in
many sizes.
Does resistor size have
anything to do with
resistor value?
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Resistor Size vs. Value
No, size has
nothing to do
with resistance
value.
Resistor size has to do
with power rating.
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Resistor
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A resistor will drop (or use) some of the supplied
voltage as current passes through it.
This creates a voltage drop across the resistor.
A resistor will have a voltage drop across it and
current flowing through it.
These two things multiplied together are the
electrical definition of power.
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Resistor
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A resistor consumes power as it does its job of
limiting current.
A resistor is not designed to produce heat, but
heat is produced when power is consumed.
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This is called self-heating.
A resistor needs to be able to dissipate the heat it
generates.
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Or it will burn up
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Since a device loses heat
through its surface, the
larger the surface area, the
more heat a device
dissipates.
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Heat dissipation is related to
device surface area.
Larger devices have a larger
surface area.
A physically larger device is able
to dissipate more heat and
handle more power.
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Heat Dissipation Formula
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Q = heat
ρ = heat transfer coefficient
A = surface area of device
Δt = temperature change or difference
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Heat Dissipation Formula
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Heat creates a temperature difference.
At a large temperature, the device will burn up.
For a given heat, a larger area results in a smaller
temperature difference.
This means a device with a larger surface area
can consume more heat before it reaches a point
where it burns up.
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Team Challenge
Goal
 Analyze the relationship
between voltage, current,
and resistance in an
electronic circuit.
Materials List (per team)
 Calculator
 Multimeter and leads
 One 470W resistor
 One 1.0KW resistor
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One 1.5KW resistor
One 1.0MW resistor
Breadboard
Breadboard wire pack
(pre-trimmed wires for
making connections on
the breadboard)
6V battery pack (includes
4 – “AA” batteries)
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Team Challenge
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Team Challenge
1.
2.
3.
4.
Connect battery to the ends of the “+” and
“-” rows with the red wire going to the “+” and the
black wire going to the “-”.
Place the 470 resistor with one end in a hole in one
column and the other end in a hole in another column.
Connect a small wire from a hole in the “+” row into a
hole corresponding to the column where one end of
the resistor is connected.
Connect a small wire from a hole in the “-” row into a
hole corresponding to the column where the other end
of the resistor is connected.
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Team Challenge
5. The breadboard layout should
resemble the image at right.
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To measure the voltage
across the resistor, use the
following setup and verify
that the batteries are
producing approximately
6.0V. Be sure to set the
multimeter on the 20 setting in
the DC Voltage setup area so
that it will be able to measure
6.0V without over-ranging.
Record the voltage measurement.
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Team Challenge
6.
Measure the current in the
circuit.
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Insert the meter between the “+”
row and the upper side of the
resistor (remove the little wire that
was connecting this side of the
resistor to the “+” row).
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Team Challenge
Verify that your current calculation was accurate.
Be sure to set the multimeter on the 20m setting in
the DC current setup area.
9. Be sure that your red lead is connected to the
“mA” connection of the meter instead of the “V”
connection.
10. Record your current measurement.
7.
8.
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Observations and Analysis
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Were there slight differences in your measured values
from your calculated values?
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Why or why not?
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