Download Activity 6.2.3 Resistance

Activity 6.2.3 Resistance
Introduction
Resistance to current flow in a circuit can be good or bad. Even the best conductors
provide some resistance. Electric power lines travel long distances on very good
conductors, but engineers try to improve systems to lose as little energy as possible.
Resistance is good, though, if it is protecting an electronic component. If you build a
circuit and a component gets very hot, then that is a sign that it should have been
better protected with additional resistance. Resistance can also control devices.
Increasing resistance on a speaker turns the volume down.
Equipment




Schematic Symbols Chart
Engineering notebook
Multimeter
Snap Circuits® components
o Board, voltage source, and power supply
o Red LED
o Variable resistors
o Various sizes of snap wires
Procedure
1. Complete the questions below as your teacher shows the Resistance
presentation.
a. All resistors ___________ or _____________ the flow of electrons.
b. As resistance __________________ current _______________________
c. In electrical circuits there are three factors which affect the amount of
resistance. They are:
d. Resistance is measured in __________ The abbreviation is _____.
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PLTW Gateway – Magic of Electrons Activity 6.2.3 Resistance – Page 1
e. __________ ohms = __________ resistance = __________ current
f. The basic materials in most fixed resistors are ________ and _________.
g. Color bands 1 – 2 determine ____________________. Color band 3 is the
______________. Color band 4 determines ___________ or__________.
h. Prefixes are used to eliminate __________.
i.
The prefix Kilo means __________. The abbreviation for Kilo is ____.
j.
The prefix Mega means __________. The abbreviation for Mega is ____.
k. 1 – 999 Ω
l.
How?
1000 – 999,999 Ω
How?
m. 1,000,000 Ω and up
How?
2. Complete the Schematic Symbols Chart as you learn about different electronic
components and functions.
Accuracy Calculation
Converted resistance x Tolerance % = Calculated Tolerance
For our class, our tolerance will always be 5% so
Calculated Tolerance = Converted Resistance x 0.05
Accuracy Range is reported as: Calculated resistance ± calculated accuracy
Be sure to use the same units in both resistance and accuracy.
Examples:
Color
Band 1
Color
Band 2
Color
Band 3
Calculated
Resistance
Converted Tolerance
Resistance
(± 5%)
Accuracy
Range
High
±
Low
High
±
Low
High
±
Low
3. Read the color bands on the supplied resistors, and, using the chart on the
following page, calculate the resistance, the converted resistance.
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PLTW Gateway – Magic of Electrons Activity 6.2.3 Resistance – Page 2
4. Have your instructor check your work before you calculate tolerance amount and
range.
5. Measure the amount of resistance in each resistor using the multimeter
Meter Settings
Range measures up to….
Label
200
2K
20K
200 K
2M
If the meter reading falls within the accuracy range, the resistor rating is “good.” If
the meter reading falls outside the accuracy range, the resistor rating is “bad.”
Remember:
Current will always follow
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PLTW Gateway – Magic of Electrons Activity 6.2.3 Resistance – Page 3
Band 1
Band 2
Band 3
Calculated Converted
Resistance Resistance
Tolerance
Amount
(± 5%)
Accuracy Range
Metered
Resistance
Rating
High
±
Low
High
±
Low
High
±
Low
High
±
Low
High
±
Low
High
±
Low
High
±
Low
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PLTW Gateway – Magic of Electrons Activity 6.2.3 Resistance – Page 4
Conclusion
1. Describe a system that would be dangerous if resistance were not a part of the
circuit.
2. Why are fixed resistors’ values indicated by color bands rather than printing the
numeric value on their exterior?
Use colored pencils to color the bands on the resistors below to identify the
appropriate resistance values.
300 Ω
47 Ω
21 KΩ
9.8 KΩ
560 KΩ
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PLTW Gateway – Magic of Electrons Unit 6 – Lesson 6.2 – Activity 6.2.3 – Resistance – Page 5