Resistivity

• What do all materials have regarding the flow of charge?

  Some resistance
• What happens when free electrons move through a metal wire?

  They collide with ions, causing heating

  
• What causes resistance in a wire?

  Ions resisting the flow of free electrons

  
• What factors affect resistance in a wire?

  Length, cross-sectional area, and resistivity

  
• What does the resistivity equation indicate about wire length and thickness?

  • Longer wire = greater resistance
  • Thicker wire = smaller resistance

  
• What is resistivity a property of?

  The material itself
• How is resistivity measured?

  In ohm-meters (Ω m)
• What happens to resistivity as the resistivity of a material increases?

  Resistance increases
• Why is copper used for electrical wires?

  It has low resistivity
• What characterizes insulators in terms of resistivity?

  They have very high resistivity
• What is the resistivity of copper at room temperature?

  $1.7 \times 10^{-8} \, \Omega \, m$
• What is the resistivity of aluminium at room temperature?

  $2.6 \times 10^{-8} \, \Omega \, m$
• Which cylinder is the better conductor, copper or aluminium?

  Copper

  
• What are the examiner tips regarding resistivity values?

  • Resistivity values will be provided in exams
  • Cross-sectional area is proportional to diameter squared
  • Doubling diameter quadruples area, reducing resistance by a quarter