Laboratory Investigation into the Resistance of a Filament Bulb

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Aim: Does the resistance of a filament bulb change as the bulb gets brighter?

Hypothesis: I believe that a filament bulb will have an increasing resistance depending upon the current passing through it.


*Power Supply




*Filament bulb with holder

*Alligator clips



1.Set up the circuit according to the schematic diagram

2.Use the alligator clips to connect the filament bulb to the voltmeter

3.Connect the power supply to the electricity

4.Make sure the switch is closed.

5.Measure and note down the temperature of the bulb with the thermometer

6.Turn on the power of the power supply

7.Measure down the P.D (v) and Current (a) and the temperature as you increase by .50 each time until 4.50 volts



Controlled Variables: Filament bulb of the same type

Independent Variables: Voltage

Dependant Variable: Current (that is what was measured due to the voltage change), Temperature (increased as bulb got brighter)


P.D. voltage

(v)Trial 1 Current (a)Trial 2 Current (a)Average Current (a)Trial 1


(Celsius) Trial 2


(Celsius) Average

Temperature (Celsius)Bulb Brightness

(scale 0-10)



I plotted my information on a graph with the P.D. on the Y axis and the Current on the X axis. In this way the slope of the graph is the resistance of the bulb. Looking at my graph I decided that there are thee separate lines that could approximate the graph. The slope of these three lines gives 3 different resistance values for the filament bulb. The resistance of the bulb increases as the current through the bulb increases. From...
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