Resistance

• The formula for resistance is: $Resis\tan ce\ (Ω)=$$\frac{Voltage}{Current}\ =$$\ \frac{V}{I}$
• Factors affecting resistance:

  • length
  • cross-sectional area
  • material
• Length is proportional to resistance because the electrons have to travel a longer length, and thus encounter more resistance: $Ω∝L$
• Resistance is proportional to cross-sectional area because more electrons can flow per unit time, increasing the current and therefore decreasing the resistance: $Ω\ ∝\ \frac{1}{A}$
• Resistance is related to the material because a better conducting material has less resistance
• Current Voltage Character of an Ohmic Resistor and a Filament Lamp

  
• Ohm’s law states that voltage across a resistor is directly proportional to the current through it. This is only true if the temperature of the resistor or lamp remains constant