Investigating components

• Investigating the resistance of different components

  1. Connect the circuit and place a filament lamp

  2. Record the voltage and current

  3. Move the dial on the variable resistor and record new voltage and current

  4. Repeat until you have six results

  5. Repeat steps 1 to 4 with a resistor and then a diode
• Variable resistor


  Allows you to change the voltage across the component
• After a certain point when you increase the voltage, the current stops increasing by as much in a filament lamp
• As the filament lamp gets hotter

  The resistance increases, so less current is able to flow
• Resistance of a resistor


  Stays constant when you change the voltage
• Current is directly proportional to voltage in a resistor


  If you double the voltage, the current will also double
• The graph for a resistor is a straight line through the origin (0 on both axes)
• Diode


  Only allows the current to flow in the opposite direction
• Resistance of an LDR

  Decreases as light intensity increases
• Security lights that only come on at night have an LDR in them
• Resistance of a thermistor

  Decreases with increasing temperature
• Fire alarms that come on when it is very hot have a thermistor in the circuit
• Some components like resistors have a constant resistance
• The resistance of bulbs, diodes, thermistors, and LDRs is not constant
• Diodes only allow the current to flow in one direction
• The resistance of a bulb increases as temperature increases
• The resistance of a thermistor decreases as temperature increases
• Identify the component that has a resistance that stays constant as you increase the potential difference
• Using the graph in Figure 3 calculate the resistance of the resistor when the current is 0.1 A