Basic Electronics Resistors Bukit View Secondary School Design & Technology Mr Siraj S.H / Mr Ong Soon Gee
<ul><li>Resistors determine the flow of current in an electrical circuit. </li></ul>Where the resistance is low the flow of current is large . Where there is high resistance in a circuit the flow of current is small.
Ohm’s Law <ul><li>( I ) Current is what flows on a wire or conductor like water flowing down a river. Current flows from negative to positive on the surface of a conductor. Current is measured in (A) amperes or amps. ( V ) Voltage is the difference in electrical potential between two points in a circuit. It's the push or pressure behind current flow through a circuit, and is measured in (V) volts. ( R ) Resistance determines how much current will flow through a component. Resistors are used to control voltage and current levels. A very high resistance allows a small amount of current to flow. A very low resistance allows a large amount of current to flow. Resistance is measured in ohms. </li></ul>Resistance is defined as the ratio of the potential difference (voltage) across a conductor, to the current flowing through it.
R= V/I A Current I V Voltage V Ω Resistance R SI Unit Name Symbol
<ul><li>Resistors are used to regulate current in a circuit. </li></ul><ul><li>Resistors are found in almost every electronic circuit. The most common type of resistor consists of a small ceramic (clay) tube covered partially by a conducting carbon film . </li></ul><ul><li>The composition of the carbon determines how much current can pass through . </li></ul><ul><li>Resistors are too small to have numbers printed on them and so they are marked with a number of coloured bands . </li></ul><ul><li>Each colour stands for a number. Three colour bands shows the resistors value in ohms and the fourth shows tolerance . </li></ul><ul><li>Resistors can never be made to a precise value and the tolerance band (the fourth band) tells us, using a percentage, how close the resistor is to its coded value . </li></ul>
The standard resistor color code table: <embed src="http://www.metacafe.com/fplayer/yt-kvQBhXo_tF0/resistor_color_codes.swf" width="400" height="345" wmode="transparent" pluginspage="http://www.macromedia.com/go/getflashplayer" type="application/x-shockwave-flash" allowFullScreen="true" allowScriptAccess="always" name="Metacafe_yt-kvQBhXo_tF0"> </embed><br><font size = 1><a href="http://www.metacafe.com/watch/yt-kvQBhXo_tF0/resistor_color_codes/">Resistor Color Codes</a> - <a href="http://www.metacafe.com/">The most popular videos are a click away</a></font> Press here to play video ±20% (M) None ±10% (K) ×0.01 Silver ±5% (J) ×0.1 Gold ×10 9 9 9 9 White ±0.05% (A) ×10 8 8 8 8 Gray ±0.1% (B) ×10 7 7 7 7 Violet ±0.25%(C) ×10 6 6 6 6 Blue ±0.5% (D) ×10 5 5 5 5 Green ×10 4 4 4 4 Yellow ×10 3 3 3 3 Orange ±2% (G) ×10 2 2 2 2 Red ±1% (F) ×10 1 1 1 1 Brown ×10 0 0 0 0 Black Tolerance Multiplier 3rd digit* 2nd digit 1st digit Color
<ul><li>Resistors can be connected together in two ways; series and parallel </li></ul><ul><li>1. Resistors in SERIES – </li></ul><ul><li>When resistors are connected in series, their values are added together: R total=R1+R2 </li></ul>For example: 1K+1K+3K9=5K9 (total value)
<ul><li>2. Resistors in PARALLEL </li></ul><ul><li>When resistors are connected in parallel, their total resistance is given as: </li></ul><ul><li>1/Rtotal = 1/R1 + 1/R2 </li></ul>For example: 1/Rtotal = 1/1K + 1/1K = 0.5K or 500 ohms OR = R1 x R2 R1 +R2 = 1 x 1 = 1 1 +1 = 2 = 0.5k