Daily Sprint START In your own words describe the functions of the following: • variable resistor • photoresistor • fixed resistor
Daily SprintSTART
In your own words describe the functions of the following:
• variable resistor
• photoresistor
• fixed resistor
MSA Prep
To find the volume of a few small marbles, a student will need which of the following scientific tools?
A. a balance and a centimeter ruler
B. a spring scale and a calculator
C. a graduated cylinder and water
D. a microscope and a micron ruler
Conclusion Questions
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?
Resistance in Circuits
Variable ResistorsA resistor whose value can be varied between its minimum and maximum values
Symbol for Circuit Diagrams
Variable ResistorsIn 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?
DC
PhotoresistorsA light-sensitive device in which the internal resistance changes with a change in light intensity
Symbol for Circuit Diagrams
PhotoresistorsIn 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?
Fixed ResistorsResistors with a value that cannot be changed
Symbol for Circuit Diagrams
Fixed ResistorsIn 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.
DC
Measuring Resistance
Ohm (Ω): The unit of measure of electrical resistance
More Ohms = More Resistance = Less Current
Measuring Resistance
• A few volunteers will measure the resistance of a few different resistors for us.
Resistance Color Codes
1st Band1st Digit
2nd Band2nd Digit
3rd BandNumber of Zeros
4th BandTolerance
Black 0 0
Brown 1 1 0
Red 2 2 00
Orange 3 3 000
Yellow 4 4 0,000
Green 5 5 00,000
Blue 6 6 000,000
Violet 7 7
Gray 8 8
White 9 9
Gold +/- 5%
Silver +/- 10%
Band 1 Band 2 Band 3 Band 4
Orange White Brown Gold
3 9 0 +/- 5% 390 Ω +/- 5%
Band 1 Band 2 Band 3 Band 4
Red Red Orange Gold
2 2 000 +/- 5% 22000 Ω +/- 5% or
22 KΩ +/- 5% Complete the Resistance Color Codes chart in Activity 6.2.3 Resistance.
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?
Resistance Color Codes
1st Band1st Digit
2nd Band2nd Digit
3rd BandNumber of Zeros
4th BandTolerance
Black 0 0
Brown 1 1 0
Red 2 2 00
Orange 3 3 000
Yellow 4 4 0,000
Green 5 5 00,000
Blue 6 6 000,000
Violet 7 7
Gray 8 8
White 9 9
Gold +/- 5%
Silver +/- 10%
Band 1 Band 2 Band 3 Band 4
Orange White Brown Gold
3 9 0 +/- 5% 390 Ω +/- 5%
Band 1 Band 2 Band 3 Band 4
Red Red Orange Gold
2 2 000 +/- 5% 22000 Ω +/- 5% or
22 KΩ +/- 5% Complete the Resistance Color Codes chart in Activity 6.2.3 Resistance.
Image Resources
Microsoft, Inc. (2009). Clip Art. Retrieved January 13, 2009, from http://office.microsoft.com/en-us/clipart/default.aspx