1. Daily Sprint
START
In your own words describe the functions of the following:
variable resistor
photoresistor
fixed resistor

2. MSA Prep
To find the volume of a few small marbles, a student will need which of the following scientific tools?
a balance and a centimeter ruler 
a spring scale and a calculator 
a graduated cylinder and water
a microscope and a micron ruler

3. Conclusion Questions
Describe a system that would be dangerous if resistance were not a part of the circuit.
Why are fixed resistors’ values indicated by color bands rather than printing the numeric value on their exterior?

4. Resistance in Circuits
Gateway To Technology
Unit 6– Lesson 6.2 – Electronics
Resistance in Circuits

5. Symbol for Circuit Diagrams
Resistance
Gateway To Technology
Unit 6– Lesson 6.2 – Electronics
Variable Resistors
A resistor whose value can be varied between its minimum and maximum values
The pictured components are potentiometers which can be used to control voltage if all three connections are used. In most applications only the center terminal and one other are used to control the potentiometer. In this scenario the potentiometer technically functions as a Rheostat by controlling the current flow.
Variable resistors are used to control things like radio volume and blower speeds in vehicles.
Symbol for Circuit Diagrams

6. Resistance
Gateway To Technology
Unit 6– Lesson 6.2 – Electronics
Variable Resistors
In your engineering notebook, draw a circuit diagram using a DC source that will power an LED and is controlled by a variable resistor.
Build the circuit you designed and adjust the potentiometer.
Did the light turn on?
Was the LED turned in the right direction?
How did the LED behave when everything was laid out correctly?
The second image is using a 5K potentiometer.
Students will likely have the best results using a red LED because they tend to light with less current. It may also may help to dim the lights in the room to better see the light’s power gradually increasing.

7. Symbol for Circuit Diagrams
Resistance
Gateway To Technology
Unit 6– Lesson 6.2 – Electronics
Photoresistors
A light-sensitive device in which the internal resistance changes with a change in light intensity
Photoresistors are also commonly called photocells or cad cells.
The clock pictured makes train sounds at every hour unless the photo resistor senses darkness.
Symbol for Circuit Diagrams

8. Resistance
Gateway To Technology
Unit 6– Lesson 6.2 – Electronics
Photoresistors
In your engineering notebook, draw a circuit diagram using a DC source that will power an LED and is controlled by a photoresistor.
Build the circuit that you designed (you may want to space the photoresistor far from the LED).
Cover and then use a flashlight to adjust the amount of light reaching the photoresistor.
What is the relationship between resistance and light levels of the photoresistor?
The second image uses a 5K potentiometer.
Students will likely have the best results using a red LED because they tend to light with less current. It may also may help to dim the lights in the room to better see the light’s power gradually increasing.

9. Symbol for Circuit Diagrams
Resistance
Gateway To Technology
Unit 6– Lesson 6.2 – Electronics
Fixed Resistors
Resistors with a value that cannot be changed
Students should be able to recognize the diodes on the circuit pictured on the right as well as the resistors.
The resistors in the right image all have a blue coating.
Symbol for Circuit Diagrams

10. Resistance
Gateway To Technology
Unit 6– Lesson 6.2 – Electronics
Fixed Resistors
In your engineering notebook, draw a circuit diagram using a DC source that will power an LED and includes a fixed resistor.
Build the circuit as shown so that you can easily insert various resistors.
Use 4 different resistors. Place them in order from most to least resistance.
Remember that the higher the resistance, the dimmer the light will be.
The second image uses a 5K potentiometer.
Students will likely have the best results using a red LED because they tend to light with less current. It may also may help to dim the lights in the room to better see the light’s power gradually increasing.

11. Resistance
Gateway To Technology
Unit 6– Lesson 6.2 – Electronics
Measuring Resistance
Ohm (Ω): The unit of measure of electrical resistance
More Ohms = More Resistance = Less Current

12. Measuring Resistance
A few volunteers will measure the resistance of a few different resistors for us.

13. Resistance Color Codes
Gateway To Technology
Unit 6– Lesson 6.2 – Electronics
Resistance Color Codes
1st Band
1st Digit
2nd Band
2nd Digit
3rd Band
Number of Zeros
4th Band
Tolerance
Black
Brown 1
Red 2 00
Orange 3
000
Yellow 4
0,000
Green 5
00,000
Blue 6
000,000
Violet 7
Gray 8
White 9
Gold
+/- 5%
Silver
+/- 10%
Band 1
Band 2
Band 3
Band 4
Orange
White
Brown
Gold
/- 5%
390 Ω +/- 5%
Band 1
Band 2
Band 3
Band 4
Red
Orange
Gold
/- 5%
22000 Ω +/- 5% or
22 KΩ +/- 5%
Complete the Resistance Color Codes chart in Activity Resistance.

14. Measuring Resistance Did you have the resistors in the right order?
Gateway To Technology
Unit 6– Lesson 6.2 – Electronics
Measuring Resistance
Remove the resistor from the circuit.
Touch the ends of the probe to the wires.
If your multimeter requires you to adjust the range manually:
Start with largest resistance value and adjust it lower until you get a reading of 1.
Go back one position and use that setting.
In your engineering notebook, record the values for each of the resistors you measured.
Did you have the resistors in the right order?

15. Resistance Color Codes
Gateway To Technology
Unit 6– Lesson 6.2 – Electronics
Resistance Color Codes
1st Band
1st Digit
2nd Band
2nd Digit
3rd Band
Number of Zeros
4th Band
Tolerance
Black
Brown 1
Red 2 00
Orange 3
000
Yellow 4
0,000
Green 5
00,000
Blue 6
000,000
Violet 7
Gray 8
White 9
Gold
+/- 5%
Silver
+/- 10%
Band 1
Band 2
Band 3
Band 4
Orange
White
Brown
Gold
/- 5%
390 Ω +/- 5%
Band 1
Band 2
Band 3
Band 4
Red
Orange
Gold
/- 5%
22000 Ω +/- 5% or
22 KΩ +/- 5%
Complete the Resistance Color Codes chart in Activity Resistance.

16. Resistance
Gateway To Technology
Unit 6– Lesson 6.2 – Electronics
Image Resources
Microsoft, Inc. (2009). Clip Art. Retrieved January 13, 2009, from