More Resistors Activity 6.2.3a Magic of Electrons © 2011 Project Lead The Way, Inc.

Variable Resistors Potentiometers More Resistors PLTW Gateway Unit 6 – Lesson 6.2 – More Resistors Variable Resistors Potentiometers Also called Pots, these resistors change the amount of resistance mechanically. They can also be used to alter the volume of a radio or change the brightness of a lamp. Potentiometers equipped with a plastic thumbwheel or a slot for a screwdriver blade are called trimmers. They are designed for occasional adjustment.

Resistance PLTW Gateway Unit 6– Lesson 6.2 – Electronics Variable Resistors A resistor whose value can be varied mechanically 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. Schematic Symbol For Potentiometers

Resistance PLTW Gateway Unit 6– Lesson 6.2 – Electronics Potentiometer Lab On your activity sheet, draw a schematic diagram using a 3 volt DC source that will power two LEDs in parallel, and includes a fixed resistor on only ONE of those LEDs. Build the circuit as shown so that you can easily insert various resistors. Schematic Symbol For Potentiometers

Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Potentiometer Lab Identify the color bands on the supplied resistors and calculate the resistor amounts. Rank your resistors 1 through 5, with #1 the resistor having the smallest amount of resistance, and #5 with the greatest amount of resistance. Follow the rest of the instructions on your activity sheet, answering the questions as work through the lab.

Finish this statement: The __________resistance, the Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Finish this statement: The __________resistance, the brighter the light.

Variable Resistors Thermistors Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Variable Resistors Thermistors TEMPERATURE SENSITIVE resistors. INCREASING the temperature DECREASES the resistance.   Schematic Symbol For Thermistors A thermistor (short for “thermal resistor”) is made of semiconductor materials and limits or restricts the flow of electrons based on temperature. While typical resistors are designed to maintain consistent resistance regardless of temperature, a thermistor's resistance varies significantly as the temperature changes.

Resistance PLTW Gateway Unit 6– Lesson 6.2 – Electronics Thermistor Lab On your activity page, draw a schematic diagram of a series circuit powered by 3 DC volts that contains an LED and a thermistor. Follow the instructions in your activity worksheet to complete this lab. Be sure to answer all questions completely, and to get your instructor’s signature verifying your finished circuit.

Either symbol can be used Resistance PLTW Gateway Unit 6– Lesson 6.2 – Electronics Variable Resistors Photoresistors A light-sensitive device in which the internal resistance changes with a change in light intensity Schematic Symbols For Photoresistors Either symbol can be used

Variable Resistors Photoresistors Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Variable Resistors Photoresistors Also called PHOTOCELLS, these resistors are made from a light sensitive material. The light-sensitive part of this LDR (light dependent resistor) is a wavy track of cadmium sulphide. Light energy triggers the release of extra charge carriers in this material, so that its resistance falls as the level of light increases. When light is BRIGHT, resistance is LOW. When light is DIM OR DARK, resistance is HIGH. The clock pictured makes train sounds at every hour unless the photo resistor senses darkness.

Resistance PLTW Gateway Unit 6– Lesson 6.2 – Electronics Photoresistors On your activity page, draw a schematic diagram of a series circuit that uses 3 DC volts that will power an LED and is controlled by a photocell. Following the instructions found on your activity sheet, build the circuit that you designed (you may want to space the photocell far from the LED). Cover and then use the lamp to adjust the amount of light reaching the photocell. Be sure to answer all the questions as you complete the activity.

Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Image Resources Microsoft, Inc. (2009). Clip Art. Retrieved January 13, 2009, from http://office.microsoft.com/en-us/clipart/default.aspx