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Science

Voltage, current and resistance

The filament lamp

You should be able to recognise the graph of current against voltage for a filament lamp.

Background

a circle with a diagonal cross through the middle.

Filament lamp symbol

The filament lamp is a common type of light bulb. It contains a thin coil of wire called the filament. This heats up when an electric current passes through it and produces light as a result.

Ohm's Law revisited

 graph showing current on the y axis and voltage on the x axis. A line is drawn through the centre of the graph at 45 degrees.

Relationship between current and voltage when a resistor follows Ohm's Law

Remember that the current flowing through a resistor at a constant temperature is directly proportional to the voltage across the resistor. The graph shows what happens to the current and voltage when a resistor follows Ohm's Law.

The filament lamp

current on the y axis and voltage on the x axis. A slightly curved line goes through the graph at 45 degrees.

Relationship between current and voltage for a filament lamp

The filament lamp does not follow Ohm's Law. The resistance of a filament lamp increases as the temperature of its filament increases. As a result, the current flowing through a filament lamp is not directly proportional to the voltage across it. This is the graph of current against voltage for a filament lamp.

Back to Producing and measuring electricity index

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