Other Calculator Functions Talk about change button Put Calculator in Write View (If doesn’t say w-view at top, go to Setup menu, press 2, press 0) Talk about a/b button. Moving left and right to correct mistakes. Back space button Using previous answer Storing and recalling numbers Changing from Degree to Radian in SET UP x -1 button Pi button Sqrt button Negative button Using parenthesis a lot for parallel resistors PEN vs DEC mode

Chapter 5: Resistors

What is a resistor? Definition: A device used in electrical circuits to maintain a constant relation between current flow and voltage. Resistors are used to lower the voltage at different points in a circuit Resistors work as they turn voltage energy into heat 2 Functions:  To limit current  To produce desired voltage Analogy

Resistors

Resistor’s Schematic Symbol Composed of a zig- zag line What is the value of the resistor on the right? Reference Designators 300 Ω 30kΩ

Surface Mount vs. Through Hole Surface Mount Through Hole

Types of Fixed Resistors Carbon Composition Metal Film Metal-Oxide Film Resistor Networks Wirewound Resistors Old-skool Low noise and good thermal properties Many packaged resistors High accuracy at high resistance High power applications High accuracy

Surface Mount Resistors (SMT) Surface Mount Technology

Resistor Properties Value in Ohms Accuracy Power rating (We’ll look at this one first)

What is Resistor Power Rating? Examples:  ¼ watt, ½ Watt, 20 watts P = V·I = V 2 /R = I 2 R Heat Sinks

Determining Value and Accuracy Tolerance Color Code: Brown = 1% Red = 2% Gold = 5% Silver = 10%

Video See lecture notes first o_tF0 o_tF0

More in class practice problems Blue Blue Blue Gold Brown Black Red Silver Brown Black Orange Silver Orange Violet Black Gold Find tolerance range as well … or you can just measure it with an Ohmmeter! 66 MΩ +/- 3.3 MΩ 1000 Ω +/- 100 Ω Ω +/ Ω 37 Ω +/ Ω

Reading Resistor Value on a Surface Mount Resistor ,000 Ω 67 Ω 10k Ω 10 Ω Potentiometers are written on the same way

What color is the following? Green Black Blue Violet

What color is the following? Brown Red Orange Violet

Homework Do problems 1 and 2 on page 85  Include the range (if applicable)!

Variable Resistors Variable resistors are designed so that their resistance values can be changed A potentiometer is a three terminal variable resistor used to divide voltage A rheostat is a variable resistor used to control current

Pictures of Variable Resistors

Linear vs. Logarithmic “Pots”

Knob rotation (Usually 20 turns) See page 69 for schematic of application Linear vs. Logarithmic “Pots”

“The larger the cross-sectional area of the conductor, the more electrons are available to carry the current, so the lower the resistance. The longer the conductor, the more scattering events occur in each electron's path through the material, so the higher the resistance. Different materials also affect the resistance.” Resistance of a Wire The longer a wire is, the more resistive it is. The thicker a wire is, the less resistive it is. (Think parallel) (Also think of a fire hose. There is always pressure drops across a pipe, but less pressure drop for bigger hoses.) Resistance is given by the following equation Therefore as a wire gets longer, the resistance change gets linearly larger.

Resistors that change resistance with temperature (Page 70 in book) RTD’s (Need to be powered) Bolometers - Thermistors (NTC) /Barreters (PTC) Thermocouples (produces a voltage) Negative vs. Positive Temperature coefficient.

Bad Resistors Resistors can go bad when too much current is passed through them. Signs of a resistor that has gone bad are: Burned or charred looking Smoky smell Melted

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