"Resistance - Download as PowerPoint"
START 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. 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 Tank (Battery) Faucet (Switch) Pipe (Wiring) What happens to the flow (current) if a rock gets lodged in the pipe? Flow (current) decreases Resistance The opposition of current flow •As resistance increases, current decreases. •All components and wires have some resistance. •Materials that are good conductors offer little resistance. Resistance External factors that affect resistance include: Thickness Resistance Diameter Larger Diameter ------------- Less Resistance Smaller Diameter ------------- More Resistance Resistance External factors that affect resistance include: Resistance Length Longer ------------- More Resistance Shorter ------------- Less Resistance Resistance External factors that affect resistance include: Resistance Temperature Cooler ------------- Less Resistance Hotter ------------- More Resistance Variable Resistors A resistor whose value can be varied between its minimum and maximum values Symbol for Circuit Diagrams 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 DC right direction? •How did the LED behave when everything was laid out correctly? Photoresistors A light-sensitive device in which the internal resistance changes with a change in light intensity Symbol for Circuit Diagrams 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? Fixed Resistors Resistors with a value that cannot be changed Symbol for Circuit Diagrams 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 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 Band 2nd Band 3rd Band 4th Band 1st Digit 2nd Digit Number Tolerance of Zeros Band 1 Band 2 Band 3 Band 4 Black 0 0 Orange White Brown Gold Brown 1 1 0 Red 2 2 00 3 9 0 +/- 5% Orange 3 3 000 390 Ω +/- 5% Yellow 4 4 0,000 Green 5 5 00,000 Blue 6 6 000,000 Violet 7 7 Band 1 Band 2 Band 3 Band 4 Gray 8 8 Red Red Orange Gold White 9 9 Gold +/- 5% 2 2 000 +/- 5% Silver +/- 10% 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