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Investigation into the resistance of a filament lamp

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Investigation into the resistance of a filament lamp

Aim: To investigate into the resistance of a filament lamp.

Background Information

Filament Bulb

The tungsten light bulb is supported by several molybdenum wires. The ends of the support wires are imbedded in a glass button at the top of the glass support rod.

The copper and nickel led-in wires, which carry current to the filament, are supported by a glass support system.

The filament of a light bulb is a resistor of no other. When current passes through the resistor electrical energy is converted into heat. A light bulb converts current into power by the resistive element inside the light bulb.

When the power level is sufficient to raise the temperature above 1000 degrees Kelvin, visible light is produced which can help us to estimate the temperature of the filament.

The current through the

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Make sure long hair is tied backJewellery must be removedPD is increased the more current that flows through the circuit, because of this the user must take care when handling all equipment as it can get very hot after a short period of use.

Fair Test

To increase accuracy and make the test fair, results must be carried out at least 3 times and the mean result of these 3 should be taken as the final reading. To reduce anomalous results the experiment will be repeated as many times as necessary.

To make the experiment fair, we need to control the variables as well as making sure the same equipment is used all the time.






  • Ammeter
  • Voltmeter
  • Variable Resistor
  • Filament Lamp (12V)
  • Thermometer
  • Power Supply (DC 12V)


  1. Connect the wires to the DC Supply.
  2. Set the power supply to 12V.
  3. Make sure the power supply is off.
  4. Now connect the ammeter to the power supply by the connecting wires.
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onding value of the current. Read the values for current and voltage and record them on a tableOnce all the required values had been gained, the three separate results for each voltage were added together and divided by three, in order to find the average currentThese values were then plotted into a I/V characteristicgraph






Average Current(amps)

Colour of the filament


Average Current(amps)


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