Resistance

• Resistance - the opposition to a current in a system, measured in ohms.
• Factors affecting resistance:

  • current
  • temperature ; (atoms vibrate when hot )
  • length
  • light
  • voltage
• How does resistance affect current?

  • Current is inversely proportional to resistance. When resistance increases current decreases.
  • This is because as electrons flow through resistor they collide with the atoms inside.
  • This transfers energy to atoms, causing them to vibrate even more.
  • This makes it more difficult for electrons to flow through the resistor.
  • Therefore, the rate of the flow of electricity ( the current) decreases as its harder to pass through resistor.
• Hoe does temperature affect resistance?

  • Normal wires - electrons vibrate more when hot, when electrons flow through resistor they collide with other atoms more , which transfers energy, making it difficult for electrons to flow
  • Thermistor - in hotter temperature the resistance is lower,
• How does length of wire effect resistance?

  • greater length means more resistance
  • electrons have to make their way through more atoms, than in a shorter wire
• How does light effect resistance (LDR)?

  • greater intensity of light, lower resistance
  • resistance is greater when it is dark
• How does voltage effect resistance (Diodes)?

  • diode allows current to flow freely in one direction
  • meaning there is high resistance in the opposite direction, so no current can flow
• What is an 'Ohmic conductor'?

  • A conductor for which current and potential difference are directly proportional.
  • Resistance remains constant, when current changes.
  • But temperature must be constant.