rpa 4 - current/p.d characteristics

• current/p.d in a RESISTOR

  • directly proportional
  • ohmic conductor
  • only in temperature is constant
• FILAMENT LAMP

  • current is not directly proportional to potential difference
  • a high current increases the temperature which increases the temperature
• DIODE

  • we use an EXTRA RESISTOR because diodes are very easily damaged by high current
  • because we use a low current we use a sensetive ammeter called a MILLIAMMETER
  • you only get a current when the potential difference is 0.6 to 0.7 v
  • no current is produced if the potential difference is reversed because the diode has a high resistance
• current/pd rpa in an RESISTOR , FILAMENT LAMP AND DIODE:

  1. use the VOLTMETER to read the voltage across the RESISTOR
  2. use the AMMETER to read the current through the resistor
  3. record in a table
  4. adjust VARIABLE resistor to record new readings
  5. reapeat several times
  6. switch the direction of the battery ( reverse the direction of p.d)
  7. the VOLTMETER and AMMETER will give negative readings
  8. plot on a graph