How Incandescent Lamps works in gif-1

Bulbs have been used in electronics for along time and they are used in a wide range of circuits. Almost everyone has used a torch and if you look closely at the light source, it is more than likely that it is a bulb. In more recent years bulbs have been slowly replaced by LEDs as these are brighter, much more reliable, cheaper, energy efficient and have a much longer working life. They are also available in a range of colours. However, bulbs are still popular.

Look closely at a typical torch bulb. It basically consists of glass ‘bulb’, inside which is a filament made from a metal called tungsten. The glass bulb holds a gas called Argon or Nitrogen or Krypton, which increases the working life of the filament.

When current passes through the filament it illuminates brightly, giving out bright light.

Some bulbs such as the example opposite have a screw thread which means the bulb can be unscrewed from its holder and replaced, once the filament fails.

The ‘conductor’ at the bottom of this example bulb carries the current, allowing it to pass through the filament.

A number of symbols can be used to represent a bulb. Three typical symbols are shown opposite. These are often seen in examinations and consequently it is important to know them.

Two versions of the same circuit are shown below. The conventional circuit diagram (on the left) shows the filament bulb lighting brightly when the switch is turned on. The current flows through the filament, causing light to be emitted.
In the pictorial circuit diagram on the right the components are shown as pictures rather than symbols.

This basic circuit has a battery as the electrical ‘source’ and a filament bulb. The bulb is called the ‘load’ as it does all the work in the circuit (ie. it lights).



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