Daily Sprint

1. What is a resistor?

2. Name and describe the different types of resistors.

3. Draw a circuit diagram with a DC source, a photoresistor, and a motor.

START

MSA Problem

Sarah mixes salt and sugar together in a small bowl. Which of the following describes a property of the mixture?

A. It is soluble in water.

B. It is magnetic.

C. It is metallic.

D. It is liquid.

Quick Review

1. Diodes can be used to protect electronic components from current flowing in another direction. Describe another application outside of electronics where it would be important for something to flow in only one direction.

2. Describe three objects in your house that utilize LEDs.

Quick Review

3. Use the Internet to research the use of LED systems to replace general household lighting. Describe one advantage and one disadvantage of replacing standard light bulbs with LED lighting.

Resistance

Resistance

• Resistance• Variable Resistors• Photoresistors• Fixed Resistors• Measuring Resistance• Resistance Color Codes

This presentation is intended to be used with Activity 4.2.3 Resistance.

Resistance

Resistance: The opposition of current flow

What happens to the flow (current) if a rock gets lodged in the pipe?

Flow (current) decreases

Tank (Battery) Faucet (Switch)

Pipe (Wiring)

ResistanceThe opposition of current flow

•As resistance increases, current decreases.

•All components and wires have some resistance.

•Materials that are good conductors offer little resistance.

ResistanceExternal factors that affect resistance include:

Thickness Resistance

DiameterLarger Diameter ------------- Less Resistance

Smaller Diameter ------------- More Resistance

ResistanceExternal factors that affect resistance include:

Resistance

LengthLonger ------------- More Resistance

Shorter ------------- Less Resistance

ResistanceExternal factors that affect resistance include:

Resistance

TemperatureCooler ------------- Less Resistance

Hotter ------------- More Resistance

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 5 different resistors. Place them in order from most to least resistance.•Remember that the higher the resistance, the dimmer the light will be.

DC

Design Your Own

• With your team, design a circuit where the living room light will turn on when the front door is kept closed.

• Innovate your circuit to include an override switch that can turn off the light even when the door is closed.

(Use correct symbols)

Design Your Own

• With your team, design a circuit for a garage door that when headlights shine on the garage door the motor will run and open the door.

• Innovate your circuit to include a push-button switch that will also open the door even when there are no headlights shining on it.

(Use correct symbols)

Measuring Resistance

Ohm (Ω): The unit of measure of electrical resistance

More Ohms = More Resistance = Less Current

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