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“The Science Behind It” |
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Navigation |
The scientific aspects of this project |
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How Bulbs Work Incandescent
Lamps Incandescent lamps work with a very simple
circuit. There is a high value resistance wire inside a
glass bulb filled with inert (non-reactive) gas. The high resistance wire is usually made from a
coil of tungsten which is an element with high resistivity (a measure of how
hard it is for electrical current to flow through something). This resistivity is increased because the wire is
very thin (restricting current flow), very long (meaning the current has to
do more work to get through the wire), and is allowed to get hotter over time
(which again makes it harder for current to flow through the wire). The wire gets hot because of the amount of
resistance, and so it begins to glow, emitting white light which can be used
to light things up! However incandescent bulbs are inefficient in
terms of power used to generate light because most of the power is turned
into heat to make the wire hot enough to emit light.
CFLs have a much more complicated way of working.
They contain many electrical components which
take the 230V AC power supply and change it into DC Current at a voltage of
about 375V. This high voltage is then connected across the
bulb tube. The bulb tube contains a tiny amount of mercury,
which is almost all in vapour form. When the high voltage flows through the
mercury in the bulb tube, it excites the particles in the mercury making it
emit light in the form of UV rays (which are invisible to humans). To make these UV rays into light that is visible
to humans, phosphorus compounds are “painted” on the inside of
the bulb tube and when the UV rays hit it, it gives off visible light. CFL’s are energy efficient as very little
energy is wasted in heat compared with an incandescent lamp. Mercury Test To prove that mercury has an
effect on living things an experiment was set up where yeast was subjected to
different quantities of mercury ions in its “environment”. The yeast was also given a sugar
solution so that it could respire (make energy for the cells to use). The yeast when respiring correctly
forms a froth of Carbon Dioxide bubbles on top of the solution over a period
of time. Enzymes are responsible for the
successful respiration reaction (Glucose + Oxygen à Ethanol + Carbon Dioxide + Water) as
they catalyse the reaction. With higher concentrations of
mercury added to the yeast there was increasingly less froth on top of the
yeast (compared with the froth on the yeast with no added mercury) due to the
toxic effects of the mercury. Mercury is a heavy metal and is
poisonous because of its effects on enzymes in the bodies of living things. Enzymes (biological catalysts)
allow important chemical reactions to take place in the body at a much lower
temperature than would be required to do the reaction without them. Mercury poisons enzymes because of
it the way its compounds/ions react with other materials. When these reactions do not take place,
the right chemicals are not produced, which can result in serious health
issues for the organism involved.
In this case the mercury poisons
the enzymes responsible for catalysing the reaction for anaerobic respiration
so the reaction doesn’t take place and carbon dioxide is not produced.
The interference that CFLs cause with AM radios is electro-magnetic
interference. This is caused by the electrical components contained in the
bulb, mainly the inductor coil and transformer. Electro-magnetic interference is when
electromagnetic radiation (in this case caused by the rapidly changing
currents inside the inductor coil) interferes with other electromagnetic
waves (in this case the AM radio waves) of the same/similar frequency. The lower AM frequencies are the same
as those the inductor coil of the bulb emits but are not in phase (radiating
out at the same time). This means the waves cancel each
other out or build each other up in different places creating the annoying
buzzing sound heard through the speakers. As higher AM and FM frequencies are
different wavelengths to the waves emitted by the inductor coil in the bulb,
they do not interfere as much if the waves are out of phase. The range of the waves from the bulb
is also very short. This means there is less interference
the further away the bulb is from the radio. |
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