Download Research for the torch (second IA)

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Research for the torch (second IA) (secondary research)
How Light Bulbs Work – Lighting up Our Lives
The Power
Okay. Light bulbs (known as incandescent) are really quite simple, and simply brilliant. The
bulb has two metal contacts at the bottom of the base where they get their power from.
These touch the electrical circuit in the fitting attached to your mains electricity, or any
number of batteries, if we’re talking flashlights. The electrical charge used to light the bulb
travels through it from one contact to the other in a loop. After hitting one contact the
current goes up a wire to a filament, which is held on a supporting glass mount in the bulbs’
centre, then travels across it, down another wire identical to the first, and on to the other
contact.
A Fundamental Filament
This filament is central in importance to the light bulb as well as central in position. It is
made out of tungsten, which is a metal with an extremely high melting point, and it certainly
needs one. After the light bulb is switched on, the tungsten filament is heated to between
an incredible 2,200 and 2,500 degrees Centigrade! As well as its’ own properties, to further
stop it burning up; the glass bulb does not contain any oxygen, but instead holds an inert
gas called argon or a mixture of argon and nitrogen for all regular bulbs or krypton/xenon
instead of the argon for more expensive premium models. (What about halogen bulbs?
We’ll get to them later).
The filament is also tremendously long and thin. For example; in a standard 60 watt bulb the
tungsten wire is over six feet long, but at the same time, it is less than one-hundredth of an
inch in diameter. So how does it fit into such a tiny space? It’s double coiled, that’s how.
Wound up tight to produce a first coil, then this coil is re-wound again to make the smaller
than an inch filament that can be seen inside the bulb.
Good Vibrations
So the electrical charge heats up the filament to produce the light. How? The electrons that
make up the electricity current rocket along, slamming into the tungsten atoms and causing
them to vibrate. This friction produces heat or thermal energy, which is captured and then
released by the electrons in the form of photons (light). Most of these are unfortunately in
the lower end of the spectrum (known as infrared) and are invisible to humans. But the
hotter the filament, the higher wavelength visible photons are emitted which we can see,
and the brighter the light from the bulb.
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Size Matters
Higher wattage bulbs have longer filaments, so they produce more light from having more
atoms to vibrate, and conversely, low voltage light bulbs have shorter coils so the light is
dimmer.
In a three-way light bulb, there are two filaments present with one being larger than the
other. When the setting is on low, then only the small filament is used, so the light is dim. If
the setting is put to medium, then only the larger filament has current travelling through it,
and the smaller one is cut off from the flow. When the setting is on high; both filaments are
in use together and the light is therefore very bright. To control this there are three
connections (for the three operating modes). One each for both filaments exclusive use, and
a third to be shared. A complicated switch controls the delivery of current.
Nothing Lasts Forever
So the tungsten filament is under tremendous strain, and won’t last. As the bulb is used for
more and more hours the vibration and white-hot temperatures begin to take their toll.
Increasingly the atoms from the coil will shake so much they will start to lose contact with
each other and begin splitting away from their brethren.
In old vacuum light bulbs, they would shoot off into the space inside the bulb until they hit
the glass. But with the argon or krypton inside them, modern bulbs last longer as many
tungsten atoms hit the gas atoms and bounce around randomly, hopefully to reattach
themselves to the filament if they get near enough to do so. Krypton atoms have more mass
than those of argon and get more hits, but krypton is much rarer, so you have to pay for the
benefit.
Though these light bulbs last longer, sooner or later the filament begins to disintegrate as
the tell-tale darkening of the glass bulb increases (being caused by the errant tungsten) and
your bulb will blow.
Often it might make the sound, ‘plink’, a few times and start flickering first, only to settle
down again as if teasing you, so you decide not to change it after all and put the
replacement you’ve just rummaged around for back again. Until next time you turn the
lights on, that is, when it decides to give out after all.
Despite your suspicions to the contrary, however, the bulb is not getting its’ revenge on you
for using it when not absolutely needed, or acting out of spite against humanity in general.
It really can’t help it. A weak old bulb is at correct operating temperature when turned on
for a while, but can’t reach it uniformly all the way along the filament when first switched
on. There is always a surge of electricity drawn by a light bulb being turned on because of
there being less electrical resistance in the tungsten when it is cooler. This resistance
increases as the bulb heats up, but the weak spots in the filament heat up quicker than the
rest (they have less surface area due to the evaporated tungsten atoms) and the funnelling
effect will cause these weaker areas to melt or snap due to the increased vibration.
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So most light bulbs may not last that long, but they are relatively cheap and very plentiful.
Hello to Halogen
A halogen bulb works differently. It still has the same tungsten filament inside it as do the
others, but here chemistry is employed in addition to physics to prolong its’ working life.
Inside these light bulbs, there is a halogen gas (almost always iodine) present, mixed in with
the argon or krypton. This new gas reacts with the vaporized tungsten that collects on the
glass to form chemical compounds called metal halides. These then leave the inner surface
of the bulb in a constant recycling process and return to near the filament where the
increased heat breaks down the halide into its constituent parts. The tungsten molecules
are now given to return to the filament, and the iodine molecules are free again to join up
with any more ejected tungsten.
This is known as the halogen cycle. The reaction only works successfully on the glass itself
though, rather than the bulb’s inner space, once the tungsten has condensed and will not
take place if the glass is not hot enough. Therefore halogen light bulbs have to be smaller
(which increases the heat); handmade of a special higher-grade glass known as ‘hard glass’
or of quartz to allow them not to break at this extra high temperature.
Halogen bulbs cost more, but may have a lifetime of up to triple a normal light bulb of the
same wattage, and at the same time be anything up to a fifth more efficient at producing
light.
Long Lifers and Energy Misers
Long life light bulbs certainly last a very long time, so it might be argued that halogen is a
waste of money. This is absolutely not true. A lot of these ‘long lifers’ are actually quite
inefficient.
To burn longer they burn cooler, and at lower temperatures; a smaller percentage of energy
is given off as light rather than wasted heat by the tungsten.
All light bulbs waste energy by giving off infrared light so the ‘energy misers’ out there on
the shelves waiting for your basket to pass by may be considered a worthwhile option. But
don’t be too hasty in gathering them up either. For some of these are not as good value as
the cheap and cheerful regular guys. It might be claimed that a 55 watt can replace a 60, or
a 90 will do for a 100 watt, but this is not necessarily so. Many (not all) of these ‘misers’ are
more mean and miserly with light than with energy, and although it may not be noticed,
sometimes produce less light by such a percentage factor that actually causes them to use
more watts of power for a given unit of light if you chase this down the comparison scale.
Light Bulbs Rule OK?
So that is how they work. Not encyclopedic maybe, but a brief tour of a subject that matters
to all; the incandescent electric light bulb. Still going strong after more than 120 years.
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Fluorescent lighting and LED‘s (Light Emitting Diodes) with their ‘cold light’ technology may
be pushing more and more at the margins of their rule, but traditional light bulbs are still
kings in our culture today.
How they work
A flashlight (usually called a torch outside North America) is a hand-held electric-powered
light source. Usually the light source is a small incandescent light bulb or light-emitting
diode (LED). Typical flashlight designs consist of the light source mounted in a parabolic or
other shaped reflector, a transparent lens to protect the light source from damage and
debris, a power source (typically electric batteries), and an electric power switch.
While most flashlights are hand-held, there are head or helmet-mounted flashlights
designed for miners and campers and battery-powered lights for bicycles. Some flashlights
are powered by hand-cranked dynamos or electromagnetic induction or are recharged by
solar power.
The name flashlight is used mainly in the United States and Canada. In other Englishspeaking countries, the more common term is torch or electric torch.
The circuit
Have you ever taken an electric torch to pieces to find out how it works? Look at the
diagram below which shows the arrangement of parts inside one kind of torch:
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Structure of an electric torch
Why did the designer choose this particular combination of materials? The metal parts of
the torch must conduct electric current if the torch is to function, but they must also be able
to stand up to physical forces. The spring holding the cells in place should stay springy, while
the parts of the switch must make good electrical contact and be undamaged by repeated
use.
The lamp and reflector make up an optical system, often intended to focus the light into a
narrow beam. The plastic casing is an electrical insulator. Its shape and colour are important
in making the torch attractive and easy to handle and use.
A torch is a simple product, but a lot of thought is needed to make sure that it will work
well. Can you think of other things which the designer should consider?
A different way of describing the torch is by using a circuit diagram in which the parts of the
torch are represented by symbols:
Circuit diagram of an electric torch
There are two electric cells ('batteries'), a switch and a lamp (the torch bulb). The lines in
the diagram represent the metal conductors which connect the system together.
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A circuit is a closed conducting path. In the torch, closing the switch completes the circuit
and allows current to flow. Torches sometimes fail when the metal parts of the switch do no
make proper contact, or when the lamp filament is 'blown'. In either case, the circuit is
incomplete.
.
Current
An electric current is a flow of charged particles. Inside a copper wire, current is carried by
small negatively-charged particles, called electrons. The electrons drift in random directions
until a current starts to flow. When this happens, electrons start to move in the same
direction. The size of the current depends on the number of electrons passing per second.
Current is represented by the symbol I, and is measured in amperes, or 'amps', A. One
ampere is a flow of 6.24 x 1018 electrons per second past any point in a wire. That's more
than six million million million electrons passing per second. This is a lot of electrons, but
electrons are very small and each carries a very tiny charge.
In electronic circuits, currents are most often measured in milliamps, mA, that is,
thousandths of an amp.
.
Voltage
In the torch circuit, what causes the current to flow? The answer is that the cells provide a
'push' which makes the current flow round the circuit. When the cells are new, enough
current flows to light the lamp brightly. On the other hand, if the cells have been used for
some time, they may be 'flat' and the lamp glows dimly or not at all.
Each cell provides a push, called its potential difference, or voltage. This is represented by
the symbol V , and is measured in volts, V.
Typically, each cell provides 1.5 V. Two cells connected one after another, in series, provide
3 V, while three cells would provide 4.5 V:
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Cells connected in series
Which arrangement would make the lamp glow most brightly? Lamps are designed to work
with a particular voltage, but, other things being equal, the bigger the voltage, the brighter
the lamp.
Strictly speaking, a battery consists of two or more cells. These can be connected in series,
as is usual in a torch circuit, but it is also possible to connect the cells in parallel, like this:
Cells connected in parallel
A single cell can provide a little current for a long time, or a big current for a short time.
Connecting the cells in series increases the voltage, but does not affect the useful life of the
cells. On the other hand, if the cells are connected in parallel, the voltage stays at 1.5 V, but
the life of the battery is doubled.
A torch lamp which uses 300 mA from C-size alkaline cells should operate for more than 20
hours before the cells are exhausted.
Which way does the current flow?
One terminal of a cell or battery is positive, while the other is negative. It is convenient to
think of current as flowing from positive to negative. This is called conventional current.
Current arrows in circuit diagrams always point in the conventional direction. However, you
should be aware that this is the direction of flow for a positively-charged particle.
In a copper wire, the charge carriers are electrons. Electrons are negatively-charged and
therefore flow from negative to positive. This means that electron flow is opposite in
direction to conventional current.
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Current flow in electronic systems often involves charge carriers of both types. For example,
in transistors, current can be carried by electrons and also by holes, which behave as
positive charge carriers.
When the behaviour of a circuit is analysed, what matters is the amount of charge which is
being transferred. The effect of the current can be accurately predicted without knowing
about whether the charge carriers are positively or negatively charged.
A cell provides a steady voltage, so that current flow is always in the same direction. This is
called direct current, or d.c. In contrast, the domestic mains provide a constantly changing
voltage which reverses in polarity 50 times every second. This gives rise to alternating
current, or a.c., in which the charge carriers move backwards and forwards in the circuit.
The Structure of an Electric Torch Light
An electric torch light is an essential tool to man, and it can be found in almost every
household and workplace in this planet. This article tries to give a basic overview of the
structure of an all important electric torch light.
A basic Electric Torch Light generally consists of several components:
Bulb - The main component that gives the light. The two most common types of bulb are
Incandescent and Light-Emitting Diode (LED) bulbs. For most torch lights, the bulb is of
incandescent type, where a tungsten filament is enclosed within a glass envelope filled with
inert gases like halogen or xenon. Light-Emitting Diode (LED) bulbs are made of
semiconductor substrates coated with phosphors, and are used because of their lower
power consumption and very long lifespan.
Reflector - A conical shaped piece of plastic or aluminium which is placed over the bulb in
the torch light. The reflector is normally coated with a highly reflective coating, and the
purpose of it is to direct the surrounding light emitted by the bulb forward. Depending on
the texture of the coating, the light beam quality may differ from a high intensity beam to a
wide area type of light.
Lens - The optics placed in front of the bulb. The lens, which can be made from clear plastics
or glass, is used mainly to protect the reflector and the bulb, and yet allow light to pass
through. Glass are less susceptible to scratches, thus are preferred over the plastic
counterpart.
Switch Mechanism - The control component of the torch light. A switch allows the user to
turn on the torch light only when necessary, thus conserving electric energy. Some torch
lights uses complex electronic circuitry within the switch, and allow special functions such as
dimming and strobing to be achieved.
Battery - Power source for the Electric Torch Light. The batteries required for the torch light
depends on the bulb being used, and they come in various sizes, from AAA to D sized.
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Alkaline batteries are still widely used, but Lithium ones are picking up due to their highest
capacity and smaller size.
Body - Normally made of aluminium or durable plastics, the torch light body is used to hold
all the other components in place. Several shape of the body is available in the market, and
the most common ones are those in a "tube" form, which allows user to hold and operate
the torch with just one hand.
With advancing technologies, the electric Torch Light is slowly evolving from a simple
handheld equipment into a complex piece of art. To know more, look out for my future
articles on torch lights!
How a Basic Fluorescent Lamp Works
General Design
The general design of a simple fluorescent lamp consists of a sealed glass tube. The tube contains a
small bit of mercury and a gas (usually argon) kept under very low pressure. The tube also contains a
phosphor powder, coated along the inside of the glass. The tube has two electrodes, one at each
end, which are wired to an electrical circuit. The electrical circuit, which includes a starter and
ballast, is hooked up to an alternating current (AC) supply.
General Operation:
When the lamp is first turned on, the current travels through the path of least resistance,
which is through the bypass circuit, and across the starter switch. This current then passes
through the circuit heating up the filament in each electrode, which are located at both
ends of the tube (these electrodes are simple filaments, like those found in incandescent
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light bulbs). This boils off electrons from the metal surface, sending them into the gas tube,
ionizing the gas. The mercury vapor becomes "excited" and it generates radiant energy,
mainly in the ultraviolet range. This energy causes the phosphor coating on the inside of the
tube to fluoresce, converting the ultraviolet into visible light.
The Starter:
The starter is basically a time delay switch. Its job is to let the current flow through to the
electrodes at each end of the tube, causing the filaments to heat up and create a cloud of
electrons inside the tube. The starter then opens after a second or two. The voltage across
the tube allows a stream of electrons to flow across the tube and ionize the mercury vapour.
Without the starter, a steady stream of electrons is never created between the two
filaments, and the lamp flickers.
The Ballast:
The ballast works mainly as a regulator. They consume, transform, and control electrical
power for various types of electric-discharge lamps, providing the necessary circuit
conditions for starting and operating them.
In a fluorescent lamp, the voltage must be regulated because the current in the gas
discharge causes resistance to decrease in the tube. The AC voltage will cause the current to
climb on its own. If this current isn’t controlled, it can cause the blow out of various
components.
Newer Designs:
Today, the most popular fluorescent lamp design is the “rapid start” lamp. This design works the
same as the basic design described above, but it doesn't have a starter switch. Instead, the lamp's
ballast constantly channels current through both electrodes. This current flow is configured so that
there is a charge difference between the two electrodes, establishing a voltage across the tube.
Another method used in instant-start fluorescent lamps, is to apply a very high initial voltage to the
electrodes. This high voltage creates a corona discharge, which causes an excess of electrons on the
electrode surface that forces some electrons into the gas. These free electrons ionize the gas, and
almost instantly the voltage difference between the electrodes establishes an electrical arc.
In Conclusion:
There are many different types of fluorescent lamps but they all work in the same basic way: An
electric current stimulates mercury atoms, which causes them to release ultraviolet photons. These
photons in turn stimulate a phosphor, which emits visible light photons
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