Resistance of a Light Bulb

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Resistance of a Light Bulb
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A circuit set up for measuring the resistance of
a light bulb
Voltmeter
Ammeter
Light Bulb (off)
Battery
Switch (open)
Rheostat
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A circuit set up for measuring the resistance of
a light bulb
Voltmeter
Ammeter
Light Bulb (on)
Battery
Switch (closed)
Rheostat
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The copper tap is not plugged in. The two copper
pieces are not in contact. Therefore the switch
is open.
The copper tap is plugged in. The two copper
pieces are in contact. Therefore the switch is
closed.
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The circuit diagram
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Voltage reading 2.5 V
Range 1 15 V
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Ammeter reading 140 mA
Range 0 500 mA
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The circuit diagram
2.5 V
140 mA
The resistance of the light bulb is 2.5 V
0.14 A 17.9 W
The rheostat is used to vary the voltage (and
hence the current) across the light bulb so that
another set of data can be obtained.
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Rheostat set to maximum resistance at the
beginning of the experiment.
The resistance of the rheostat is decreased.
Rheostat is set to minimum resistance.
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The rheostat is of minimum resistance. The
current through the bulb is strongest and the
tungsten wire is brightess.
The rheostat is of higher resistance. The current
through the bulb is just enough to make the
tungsten wire glow.
The rheostat is set to very high resistance. The
current through the bulb is too weak to enable
the tungsten wire to glow.
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The resistance of the light bulb increases as the
potential difference across it increases. This is
because the current through the tungsten wire
increases. The temperature of the tungsten wire
thereby increases. For metals, the electrical
resistance increases as the temperature increases.