daily sprint

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