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Transforming Electricity
into Light and Heat
7.1
Electricity is most commonly used to produce light. With a flick of a
light switch, electricity is sent to a light bulb and transformed, or
changed, into light and heat. An incandescent [IN-kuhn-DES-uhnt]
light bulb produces light by heating a filament [FILL-uh-muhnt]
(Figure 1). Did you know that electric lighting has only been around
since the early 1880s?
Tungsten wire filament
Glass bulb
Figure 1
The incandescent light bulb is
used in lamps to produce light.
When electricity passes through
the tungsten wire filament, it
becomes so hot that it glows
white.
How is electricity transformed into light in a light bulb?
The filament in a light bulb resists the flow of electric current.
Like a crowd of people trying to get through a narrow hall, the
electric charges meet resistance as they travel along the filament.
This makes the filament so hot that it turns red and then white.
The extreme white heat creates the light that you see. The filament
does not burn because it is made of a tough metal called tungsten.
The glass bulb surrounding the filament is filled with a gas that
does not allow burning. Eventually, the filament gets so thin that
it breaks and the bulb has to be replaced.
Have you ever touched a light bulb when it was on? If you have,
you know that not all the electricity is changed into light. Some of
the electricity is changed into heat. This heat is wasted. It goes into
the air around the light bulb and is not used for anything (Figure 2).
NEL
7.1
Light
Heat
Heat
Electricity
Figure 2
Only about 6% of the electricity
that goes into a light bulb produces
light. The rest produces heat.
Transforming Electricity into Light and Heat
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LEARNING TIP
If you find a topic difficult
to understand, read more
slowly. Go back and reread
the section as many times
as you need to until you are
sure that you understand.
Page 122
Fluorescent [flo-REHS-uhnt] light bulbs also use electricity to
produce light. A fluorescent light bulb is a glass tube that contains
gases. These gases produce a special type of light, called ultraviolet
light, when electricity is passed through them. A coating inside the
fluorescent tube absorbs the ultraviolet light and produces the light
that you see. Fluorescent light bulbs use a lot less electricity and last
much longer than incandescent light bulbs.
Light emitting diodes, or LEDs, are used in digital clocks, bicycle
lights, Christmas lights, newer traffic lights, and calculators. LEDs
are tiny solid light bulbs that are very energy-efficient (Figure 3).
They produce very little heat because they do not have a filament.
As well, they last much longer than other types of light bulbs. They
are expensive, however. As the price of LEDs falls, more and more
electrical appliances will use them.
Figure 3
An LED bulb is more durable than an
incandescent light bulb because it has
no filament and no glass bulb that
can break.
Some appliances, such as toasters, heaters, and hair dryers, are
designed to produce heat. The wires inside a toaster are similar to
the filaments in a light bulb. They resist the electric current and
produce heat. This heat toasts your bread. The wires also produce
light—the orange or red glow.
CHECK YOUR UNDERSTANDING
1. When electricity is transformed into light, another form of energy is
produced. What is it?
2. Why do many people now use fluorescent light bulbs instead of
incandescent light bulbs?
3. What are three advantages of LEDs?
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Unit B
Electricity
NEL