Lets look at the resistivity of elements on the periodic table: http://www.webelements.com/periodicity/electrical_resistivity/ 12/3/2018 Robinson Scholar

Types of Resistors 12/3/2018 Robinson Scholar

Carbon resistors Resistors are used to step down the voltage flowing through a circuit. The center of the resistor is made from a material that is only a partial conductor of electricity, like carbon. When the voltage reaches the part of the resistor that is a poor conductor, the voltage is reduced or stepped down. 12/3/2018 Robinson Scholar

Let’s Observe Resistors Make at least 4 observations of the resistors at your desk. Record your observations on the post-it notes provided. 12/3/2018 Robinson Scholar

Resistors: Reading the Resistor Color Code

Observing Resistors There is a gap between the bands that indicate resistance value and the band that represents tolerance. Values, Multipliers and Tolerances 12/3/2018 Robinson Scholar

Tolerance of resistors (fourth band of color code) Tolerance is the precision of the resistor and it is given as a percentage. For example a 390 resistor with a tolerance of ±10% will have a value within 10% of 390, between 390 - 39 = 351 and 390 + 39 = 429 (39 is 10% of 390). Find the tolerance of a 10M resistor. Calculate the range of the possible values of the resistor. Tolerance may be ignored for almost all circuits because precise resistor values are rarely required. 12/3/2018 Robinson Scholar

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First Example: 12/3/2018 Robinson Scholar

Let’s Practice with these… Determine the nominal resistance values of these resistors, given their band colors, and also express the allowable tolerance in ohms. Red, Org, Blu, Gld = 12/3/2018 Robinson Scholar

Brn, Blk, Grn, Sil = Blu, Blk, Brn, Gld = 12/3/2018 Robinson Scholar

For more practice, try these and check them with the applet on the next slide. Yel, Vio, Red, Sil = Grn, Brn, Yel = Wht, Blu, Blk, Sil = Gry, Grn, Org, Gld = Org, Org, Gld = Vio, Red, Sil, Gld = Brn, Red, Blk, Sil = 12/3/2018 Robinson Scholar

Use this applet to check your answers: http://www.abcsemiconductors.com/resistanceang/resistance.phtml 12/3/2018 Robinson Scholar

Resistors and Color Code Tutorial: http://www. youtube. com/watch Resistors and Color Code Tutorial: http://www.youtube.com/watch?v=AZ7xf6Jakbo Short Animation describing resistance: http://www.youtube.com/watch?v=qph0kBCR0ps Using a simple circuit and graphite from your pencil as a variable resistor http://www.youtube.com/watch?v=FpUdQopj1Lg&feature=related 12/3/2018 Robinson Scholar