RP: Investigating Resistivity

• What is the aim of the experiment?

  To determine the resistivity of a wire
• What are the variables in the resistivity experiment?

  • Independent variable: Length, L, of the wire (m)
  • Dependent variable: Current, I, through the wire (A)
  • Control variables: Voltage, material of the wire
• What is the length of the constantan wire used in the experiment?

  2 metres
• What is the resolution of the measuring equipment used in the experiment?

  • Metre ruler: 1 mm
  • Micrometer screw gauge: 0.01 mm
  • Voltmeter: 0.1 V
  • Ammeter: 0.01 A
• How should the constantan wire be set up for the experiment?

  It should be taped or clamped to the ruler
• What voltage should be set on the power supply?

  6.0 V
• Why should the current be switched off immediately after reading?

  To prevent the wire from heating up
• What is the method for varying the distance in the experiment?

  • Vary the distance in 0.25 m intervals
  • Record current for each length at least 3 times
  • Calculate average current for each length
• What equation is used to calculate the average resistance of the wire?

  R = V / I
• How is resistivity calculated in the experiment?

  1. Plot graph of length L against resistance R
  2. Draw line of best fit
  3. Calculate gradient
  4. Multiply gradient by cross-sectional area A
  5. Use formula: ρ = gradient × A

  
• What is the formula for calculating the cross-sectional area A of the wire?

  A = π(d/2)^2

  
• What are the systematic and random errors in the experiment?

  Systematic Errors:

  • Zero error if wire not at 0 on ruler

  
  

  Random Errors:

  • Small currents to prevent temperature increase
  • Average diameter from multiple measurements
• Why should the temperature be kept constant and low during the experiment?

  To prevent changes in resistance and resistivity
• What safety considerations should be taken during the experiment?

  • Do not touch the wire when powered
  • Switch off if burning smell occurs
  • Keep liquids away from equipment