Resistance and resistivity
- Created by: Sevdeg
- Created on: 12-05-14 07:51
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- Resistance and resistivity
- I-V graph for a resistor: Straight line passing through the origin. I is directly proportional to V.
- Resistance= 1/ Gradient of the graph
- Ohm's law: For a metallic conductor at constant temp. the current is directly proportional to the PD.
- LED and semi conductor diodes are non ohmic materials.
- I-V characteristics for a filament lamp: Line passes through origin. At higher voltages line starts to curve.
- Thermistors are made from metal oxides. There are two types of thermistors:
- 1. NTC: Resistance decreases with increasing temperature.
- 2. PTC: Resistance rises suddenly at a definite temperature.
- 2 factors affect the resistance of a metal: the temperature and impurities
- Resistance is proportional to length and inversely proportional to area.
- Resistivity: RA/L
- Resistivity increases with temp because there are more frequent collisions between electrons and ions.
- Resistivity: RA/L
- I-V graph for a resistor: Straight line passing through the origin. I is directly proportional to V.
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