p2- resistance

• Investigating how a wire's resistance depends on its length


  1. Set-up circuit

  2. Attach resistance wire to metre rule

  3. Move the crocodile clip along the wire in increments, taking measurements for voltage and current each time

  4. Calculate the resistance for each length
• Voltmeter


  Connected in parallel to the resistance wire
• Ammeter


  Connected in series with the resistance wire
• Graph of resistance against length

  The two variables are directly proportional so should produce a straight line going through the origin
• In reality, the line produced may not pass through the origin
• Zero error


  It is hard to attach the stationary crocodile clip exactly at the zero end of the metre rule
• Wire used


  • For a given material, the thinner the wire, the higher the resistance
  • This makes the recorded resistance values large enough to be measured and interpreted
• Low potential difference


  To prevent the current getting too high and the wire heating up
• Wire heating up


  Resistance of a wire will increase if the temperature increases, creating an extra variable which will interfere with the results
• Resistance increasing with temperature

  The metal ions have more kinetic energy so vibrate more. This causes them to collide more frequently with current-carrying electrons, providing more resistance against the flow of electrons
• Safety precautions


  • Avoid touching the wire since it may be very hot
  • Keep potential difference values low to avoid overheating
• Two resistors in series
• Two resistors in parallel
• Combination of resistors with least resistance

  The resistors in parallel will have a lower resistance than the resistors in series
• Total resistance of parallel combination


  The total resistance will be lower than the resistance of the smallest of the two individual resistances