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Properties of Resistors

Properties of Resistors. Current of Electricity (Part 2). Topics. Ohm’s Law Ohmic Conductor Filament Lamp Semiconductor Diode Resistivity. Previously from Part 1…. Definition of Resistance: ratio of potential difference to the Current R = V/I

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Properties of Resistors

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  1. Properties of Resistors Current of Electricity (Part 2)

  2. Topics • Ohm’s Law • Ohmic Conductor • Filament Lamp • Semiconductor Diode • Resistivity

  3. Previously from Part 1… • Definition of Resistance: ratio of potential difference to the Current • R = V/I • Note that this is the definition of resistance. This is always true, no matter what the values of V and I are. • We will now study something which is potentially confusing if you are not strong with this concept

  4. Ohm’s Law • Ohm’s Law states that the current passing through a metallic conductor is directly proportional to the potential difference across it, provided that physical conditions (such as temperature) remains constant • Important note: Ohm’s Law only holds true if it is a metallic conductor AND temperature is constant

  5. Ohmic Conductor Current P.D.

  6. Filament Lamp Current P.D.

  7. Filament Lamp • As current increases, the filament generates more heat, increasing the temperature • (Note: Ohm’s Law no longer applies when temperature increases) • When temperature increases, the resistance increases

  8. Semiconductor Diode • A semi-conductor is a non-metal, and it does not obey Ohm’s law • Some semiconductor diodes emit light, and they are called LEDs (Light Emitting Diodes) • LEDs are prevalent in technology, recently televisions also use LED technology • An ideal diode has zero resistance in one direction, but infinite resistance in the opposite direction

  9. Ideal Diode Current P.D.

  10. Real Life Diode Current P.D.

  11. Semiconductor Diode • Diodes act has one-way only gates • They are extremely useful in electronics • We will come across diodes again when we study AC Electricity

  12. Resistivity • This part of the lesson only concerns solid metal conductors • Two principles: • 1) The resistance of a conductor is directly proportional to its length • 2) The resistance of a conductor is inversely proportional to its cross-sectional area

  13. Length Resistance R Length L Resistance 2R Length 2L

  14. Cross-Sectional Area Cross-Sectional Area A Resistance R Cross-Sectional Area 2A Resistance R/2

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