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 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

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

Ohmic Conductor Current P.D.

Filament Lamp Current P.D.

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

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

Ideal Diode Current P.D.

Real Life Diode Current P.D.

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

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

Length Resistance R Length L Resistance 2R Length 2L

Cross-Sectional Area Cross-Sectional Area A Resistance R