HOW DO BULBS WORK

Thomas Edison invented many things, but the light bulb wasn’t one of them. Edison didn’t labor through a supposedly 1000 attempts to invent the bulb, but actually refined a cruder, pre-existing model. The first bulb or artificial source of light is actually known to be invented by Ebenezer Kinnersley in 1761. It was only a thread of wire that, when heated to a certain temperature, became incandescent.

JOULE HEATING
This was truly revolutionary. Over the course of the following century, what inventors were searching for was a construction that was cost-effective and was able to emit intense light for hours, but at a minimum expenditure of energy. Their expectations were no doubt quixotic. The ideal bulb would be cheap to construct, it would glow bright white for more than a thousand hours, while dissipating the minimum amount of undesired heat.

As time passed, the lone wire was soon sheltered by a glass dome. The first construction consisted of a platinum wire in one, for the metal exhibits a very high melting point. Metals like platinum glow when subjected to electricity due to the thermal energy they produce when their electrons, driven by the electric field, randomly collide with the surrounding ions. This resistive heating is analogous to frictional heating and is technically called Joule heating.

THE "YELLOW" BULB

However, while the heated filament didn’t melt, it wasn’t bright, nor did it last long enough to be commercially sold. Furthermore, as the filament was heated, the platinum would evaporate and stick to the insides of the glass dome, blackening it entirely. The evaporation would eventually cause the platinum to exhaust.

One possible substitute was carbon. When a carbon filament is subjected to electricity in a vacuum enclosed in glass, it burns much brighter. What’s more, the vacuum ensures that the carbon atoms don’t react with any gas, thus stretching the filament’s life. This delays evaporation and therefore prevents the blackening of the bulb.
Edison used the same construction, but with minor improvements. His heat-treated carbon bamboo filaments would cause the bulb to glow for more than 1000 hours! Edison is credited with the invention of the bulb because his model was viable for commercial use. His patented technology was manufactured and distributed to entire cities. In 1904, however, carbon and platinum filaments were replaced by tungsten filaments.

Tungsten has an astonishing melting point of around 3400K, which allows us to heat it to at least 3000K, a temperature at which the luminosity produced is staggering. Since then, tungsten has been exclusively used to construct incandescent bulbs. Unlike Edison’s carbon-filament bulb, tungsten bulbs aren’t sequestered in a gas-free vacuum, but rather in vacuum-sealed hard glass filled with an inert gas, such as argon. The evaporated tungsten collides with the molecules of the inert gas and is reflected back onto the filament.
However, the rate of evaporation is greater than the rate of reflection if the tungsten is heated to higher temperatures. This would be required if you wished to make the bulb brighter. To avoid premature blackening and achieve longevity, we must compromise brightness and heat the tungsten to lower temperatures. This is why the incandescent bulbs in your house glow yellow, rather than a blinding white.

HALOGEN BULBS

The bulbs that do glow blinding white are halogen bulbs. A halogen bulb also consists of a tungsten filament, but the bulb is filled, as its name suggests, with a halogen gas. Just like the inert gas in a yellow bulb, the halogen gas elongates the bulb’s life by reacting with the evaporated tungsten molecules and re-depositing them onto the filament.

However, because the rate of this reaction and redeposition is greater than the rate of evaporation, even at very high temperatures, tungsten filaments in halogen bulbs can be heated to blazing temperatures with a reduced risk of blackening. The light produced is therefore not yellow, but a stark white. Considering the dangerous temperatures, the material sheltering the apparatus is not merely hard glass, but a robust fused quartz.

The major drawback of a yellow bulb is its inefficiency: almost 95% of the energy is dissipated as heat. On the other hand, a halogen bulb is superiorly efficient and runs much longer than yellow bulbs. It is therefore no wonder that halogen bulbs cost more than incandescent bulbs. While halogen bulbs do make an appearance or two in households, they are most commonly found in stadiums, mounted in grids on soaring posts. At their maximum intensity, the grid’s artificial white light mimics the sun’s white light, generating a more “natural” setting.

However, to produce their characteristic white light, halogen bulbs are required to operate at dangerously high temperatures. If you were to touch one of them, there is a good chance of being scarred for life. The temperature also makes these bulbs potential fire hazards. Other than the ideal qualities listed above, let’s not forget the bulb should be safe to use and meets the increasingly urgent requirement of being environmentally friendly.

COMPACT FLUORESCENT LIGHT (CFL) BULB

On the other hand, Compact Fluorescent Light (CFL) bulbs pose a marginally smaller risk of fire and are more efficient and long-lasting than both incandescent and halogen bulbs. While halogen bulbs can last up to 5,000 hours, CFLs are known to last as long as 8,000 hours.

CFL bulbs contain mercury gas, which is converted to plasma when a high current passes through it. The reaction produces ultraviolet light, which our eyes are incapable of detecting. However, when this light interacts with the fluorescent coating inside the bulb on its way out, it is converted to bright white, visible light. Mercury, we know, can be lethal, but the volume of mercury in a CFL bulb is 100 times less than in a thermometer. Of course, CFLs cost more than halogen bulbs, which means they cost much more than incandescent bulbs.

Subsequently, as the technology burgeoned, efficiency enhanced many-fold. In the last 50 years, electronic technologies have been revolutionized by the advent of semiconductors. Today, our best bet is a Light-Emitting Diode (LED), one of the first offsprings of this revolution.

LIGHT EMITTING DIODES (LED)

Two blocks of semiconductors, one comprising more electrons than the other, can be coalesced to form what is called a p-n (positive-negative) junction. When a voltage is applied to this junction, the electrons from the excessively negative block are pushed towards the positive block. When these electrons occupy the vacancies inside the neighboring block, they are relegated to a lower level of energy. This lost energy is released as light.

LEDs are 75% more efficient than CFLs and can last for more than 15,000 hours! What’s more, because the mechanism lacks any joule heating, they guarantee equal or greater luminosity with absolutely no risks of fire hazards! But then, what’s the catch?

Well, LEDs are the most expensive of the lot. However, what consumers fail to realize is that the cost is justified. In fact, one tends to get more than one bargained for. In the long run, LEDs are surely the most lucrative choice, not only because they are more energy-efficient and long-lasting, but also because they’re the easiest to dispose of. Amongst the four technologies, LEDs are the most environmentally friendly.
Lastly, an LED, unlike the previous three bulbs, is much more than an artificial source of light. The ridiculous scalability of semiconductors and their meager energy demands have combined to form a device that can be easily integrated with other circuits to develop far more comprehensive projects. Semiconductors are truly the gifts that keep on giving, so who knows what we’ll get next!.

WHY DO WE USE DIELECTRIC CAPACITORS?

Dielectrics are basically insulators, materials that are poor conductors of electric current. Unlike the free electrons in a conductor, its electrons are tethered to its atoms. Consequently, no current can flow through it.

Such a material has no place in conductive devices, unless it is used to insulate itself, of course. However, if you think that dielectrics are despised by engineers, you are terribly mistaken. In fact, dielectrics are as ubiquitous as transistors. Between every capacitor is sandwiched a dielectric, the same capacitors without which your touchscreen would merely be a sheet of glass. But how does an insulator enhance the efficacy of a capacitor?

THE CAPACITOR

A capacitor is a device that consists of two parallel metallic plates placed extremely close to one another. The primary objective of a capacitor is to store charge. The charge can later be released to drive other circuits. This property renders it very useful in devices such as inverters. However, before releasing charge, it must first acquire it.

A capacitor is fed charge by connecting its plates to the terminals of a battery. Now, because metals are a sea of free electrons, when the electrons emanating from the negative terminal reach the metal, they violently repel the electrons on its surface. The repulsive force neutralizes the force exerted on the electrons by the battery, deterring them from accumulating on the plate.

The extra electrons could be accommodated if they were somehow attracted by a force greater than the force of repulsion. This is achieved by placing another metal plate parallel to it. The parallel plate is connected to the positive end of the battery. At that point, the positive terminal attracts the electrons from the plate to which it is connected, rendering it positively charged.

This positively charged plate will now provide the force of attraction we desired, meaning that it will attract the extra electrons transmitted by the negative terminal. In this way, the capacitor will store charge. This charge on the plate can be used to drive another circuit in the absence of a battery by simply connecting the wires to the negative and positive plates as they typically are to the two terminals of a battery.

WHY DIELECTRIC ENHANCE CAPACITANCE

Even though atoms in a dielectric cannot be ionized to generate a current, they can certainly be polarized. When one brings a negatively charged object towards a dielectric, the electrons in its atoms are repelled by it. This accrues a net positive charge on the side of the dielectric facing the object and, consequently, a net negative charge on the opposite side.

Now, because an army of positive charges faces the negative plate, the electrons on the plate are now bound to the plate even more tightly. Also, because the second plate faces the electrons, the electrons on the plate are now repelled with greater efficacy. This will cause the first plate to accrue an even greater number of electrons, thus increasing the overall capacitance!
Capacitance is given by the ratio of the plates’ cross-sectional area and the distance between them. Capacitance will increase if we increase the cross-section of the plate for the obvious reason that a larger plate can accommodate more charges. Capacitance decreases with an increase in the distance between the plates for the simple reason that an increased distance weakens the attractive forces that lure and bind the electrons to the second plate.

However, we have just found that capacitance is also a direct function of the ability of the medium between the plates to resist ionization. The measure of this ability is given by its permittivity. Capacitance is therefore equal to the ratio of the plates’ cross-section and the distance between them, multiplied by the permittivity of the medium between them.

In conclusion, a good dielectric is not merely an insulator, but a material that refuses to ionize at any cost. They also ensure that the plates are always separated, thereby averting the possibility of a short. An even better dielectric is also robust and capable of working at higher temperatures.

WHY DO WE USE DIELECTRIC CAPACITORS?

Dielectrics are basically insulators, materials that are poor conductors of electric current. Unlike the free electrons in a conductor, its electrons are tethered to its atoms. Consequently, no current can flow through it.

Such a material has no place in conductive devices, unless it is used to insulate itself, of course. However, if you think that dielectrics are despised by engineers, you are terribly mistaken. In fact, dielectrics are as ubiquitous as transistors. Between every capacitor is sandwiched a dielectric, the same capacitors without which your touchscreen would merely be a sheet of glass. But how does an insulator enhance the efficacy of a capacitor?

THE CAPACITOR

A capacitor is a device that consists of two parallel metallic plates placed extremely close to one another. The primary objective of a capacitor is to store charge. The charge can later be released to drive other circuits. This property renders it very useful in devices such as inverters. However, before releasing charge, it must first acquire it.

A capacitor is fed charge by connecting its plates to the terminals of a battery. Now, because metals are a sea of free electrons, when the electrons emanating from the negative terminal reach the metal, they violently repel the electrons on its surface. The repulsive force neutralizes the force exerted on the electrons by the battery, deterring them from accumulating on the plate.

The extra electrons could be accommodated if they were somehow attracted by a force greater than the force of repulsion. This is achieved by placing another metal plate parallel to it. The parallel plate is connected to the positive end of the battery. At that point, the positive terminal attracts the electrons from the plate to which it is connected, rendering it positively charged.

This positively charged plate will now provide the force of attraction we desired, meaning that it will attract the extra electrons transmitted by the negative terminal. In this way, the capacitor will store charge. This charge on the plate can be used to drive another circuit in the absence of a battery by simply connecting the wires to the negative and positive plates as they typically are to the two terminals of a battery.

WHY DIELECTRIC ENHANCE CAPACITANCE

Even though atoms in a dielectric cannot be ionized to generate a current, they can certainly be polarized. When one brings a negatively charged object towards a dielectric, the electrons in its atoms are repelled by it. This accrues a net positive charge on the side of the dielectric facing the object and, consequently, a net negative charge on the opposite side.

Now, because an army of positive charges faces the negative plate, the electrons on the plate are now bound to the plate even more tightly. Also, because the second plate faces the electrons, the electrons on the plate are now repelled with greater efficacy. This will cause the first plate to accrue an even greater number of electrons, thus increasing the overall capacitance!
Capacitance is given by the ratio of the plates’ cross-sectional area and the distance between them. Capacitance will increase if we increase the cross-section of the plate for the obvious reason that a larger plate can accommodate more charges. Capacitance decreases with an increase in the distance between the plates for the simple reason that an increased distance weakens the attractive forces that lure and bind the electrons to the second plate.

However, we have just found that capacitance is also a direct function of the ability of the medium between the plates to resist ionization. The measure of this ability is given by its permittivity. Capacitance is therefore equal to the ratio of the plates’ cross-section and the distance between them, multiplied by the permittivity of the medium between them.

In conclusion, a good dielectric is not merely an insulator, but a material that refuses to ionize at any cost. They also ensure that the plates are always separated, thereby averting the possibility of a short. An even better dielectric is also robust and capable of working at higher temperatures.

HOW DOES LIGHTERS WORK

Lighters are to smokers what sunlight is to trees, but lighters aren’t merely used to light cigarettes. They’re also quite common at any party that involves a cake dug with candles. However, have you ever wondered how lighters produce a flame so perfectly ovate, as if it materializes from a candle, out of thin air?

THE MODERN LIGHTER

The modern lighter couldn’t have been born if Austrian chemist Carl Auer Von Welsbach hadn’t invented ferrocerium, an alloy of iron and cerium, a rare metal, that emanates sparks when oxidized rapidly. One way to achieve this is to strike it against an object. The sparks, which reach temperatures of up to 3,000 ᵒC, can be used to ignite lighter fuels and cutting torches.

The modern lighter doesn’t store hydrogen, but butane. It initially stored naphtha, until we realized that butane produces a more controlled flame and exudes the least amount of unpleasant odor. Butane in a lighter is pressurized and stored, which causes it to exist as a liquid. When depressurized, the liquid will immediately vaporize to form gaseous butane. The gaseous butane, being flammable, will catch fire even when incited by the slightest of sparks.

The metallic wheel on the lighter, when pushed down by one’s thumb, will rub against the ferrocerium to produce a scorching spark. Simultaneously, a valve opens, from which the butane is released, which is vaporized (depressurized) as soon as it exits the container. The spark is produced just above the valve, which then simply ignites the plume of gas. The result is an ovate, tranquil flame.

The ‘Clippers’ or ‘Zippos’ that implement this mechanism are a delight for an aesthete, but are also more expensive. Cheaper lighters use a piezoelectric material that converts mechanical energy to electric energy. Unlike ferrocerium, a piezoelectric material isn’t pyrotechnic, but its electric resistance changes when it is deformed by mechanical forces.

When you “click” such a lighter, the piezoelectric material deforms and bears a current. Above the valve through which the butane exits, two separated wires produce between them what is called a voltaic arc, an electric discharge or plasma, like the thorns of current surrounding Thor. This discharge, like a spark, will ignite the depressurized gas and produce a candle-like flame.

The invention of an igniter is regarded to be as crucial to the progress of our civilization as the invention of the wheel, perhaps, even moreimportant. Without fire, cooking food would have been impossible, without which we would have been unable to kill its harmful germs and leverage its nutrients. It’s no wonder that Stephen Fry believes the lighter to be our greatest gadget. It allowed us to summon a member of the pantheon, at our whim, or as Fry said, with merely “the flick of our fingers.”

HOW DOES TEMPERATURE REGULATION IN AN ELECTRIC IRON WORKS?

The working of an electric iron is very simple – it takes current from the mains and heats up a coil inside it. This heat is then transferred to the base plate which is pressed against clothes to remove creases.

Back when I was learning how to iron my clothes, I was rather annoyed by the whole process. For no reason whatsoever, it kept switching on and off of its own accord. As much as I was irritated by this, I was also intrigued by the strange phenomenon. Thankfully, I soon came to know that it was the ‘automatic power cut’ feature that prompted this action in the iron.

You’ve almost certainly observed this automatic power on/off function in electric irons, but do you know how it works? How does the iron know when to cut off the power? More importantly, how does an iron go about actually doing that?

WHAT DOES THE THERMOSTAT DO IN AN ELECTRIC IRON?

The most important component that helps to regulate temperature in an electric iron is the ‘thermostat’. Everyone has heard of thermostats in reference to air conditioners, water coolers, maintaining temperature balance in the home, and a number of other appliances that deal in temperature control.

The basic function of a thermostat can be deduced from the name alone; the word is formed from two Greek words: ‘thermo’ (heat) and ‘statis’ (status quo or constant). As the name implies, a thermostat’s basic function is to keep the heat constant in a given setting.

WORKING OF AN ELECTRIC IRON

The electric iron that we use to press the creases out of our garments also contains a thermostat, which makes sure that the iron doesn’t get too hot if it’s kept switched on or left unattended for an extended period of time. Let’s take a look at exactly how the mechanism works.

An electric iron relies on a basic combination of heat and pressure to remove creases from clothes. When an electric current is passed through a coil (or any other heating element present in the iron), it gets very hot. This heat is then transferred to the base plate (the smooth, flat surface that you place against clothes while ironing) through conduction, which elegantly and precisely irons your clothes.

However, if the iron is continuously drawing electricity from the power supply, the heating element continues getting hotter. This causes a lot of energy wastage (as an iron consumes a lot of electricity even in a few minutes), ruins your clothes, and in the worst cases, causes nasty (and potentially dangerous!) accidents.

Therefore, it’s essential that the iron doesn’t heat up to hazardous temperatures. This is where the thermostat enters the picture.

BIMETTALIC  STRIP

The thermostat in an iron uses a bimetallic strip, and as the name implies, a bimetallic strip is made up of two different types of metal – with dissimilar coefficients of expansion – that are bonded together. This means that in the presence of heat, they expand differently. This bimetallic strip is connected to a contact spring through small pins.

At moderate temperatures, the contact point remains in physical contact with the bimetallic strip. However, when the temperature of the iron exceeds a certain limit, the strip begins to bend towards the metal with a lower coefficient of expansion. As a result, the strip ceases to be physically connected to the contact point, the circuit opens and current ceases to flow.

(a) Under normal temperature, (b) When the iron becomes too hot

Given that the circuit remains open for some time, the temperature of the iron drops, the strip acquires its original shape, and the current flows again. This cycle is repeated until you switch off its power supply from the main electricity source. This is the reason why your iron seems to power on and off of its own accord.

Now that we’ve cleared that up, if you thought that your iron was dysfunctional and were thinking of taking it to a electrician, you should feel proud of yourself – you just saved some money!

WHY DO POWER LINES PRODUCE A BUZZING SOUND?

While walking down a particularly empty street, especially at night, with high power lines overhead, have you ever heard a distinct buzzing sound emanating from the wires? Similar sounds can be heard close to transformers (although the mechanisms behind the sounds produced by power lines and transformers are different).

There is nothing special or remarkable about these buzzing sounds – they’re just a constant, flat ‘buzzing’ noise, but they’re hard to ignore!

Do you know why high power lines and transformers produce those flat, monotonous sounds?

Let me start by telling you that that buzzing sound actually has a name, and a pretty neat one at that!

MAINS HUM OR ELECTRIC HUM

Mains hum, electric hum or power line hum… these are the terms generally used to refer to the sounds that are produced by transformers or power lines due to the passage of alternating current at the frequency of the mains electricity. Typically, the fundamental frequency of the buzzing sound that you hear is 50 or 60 Hertz, depending on the local power line frequency. It also depends on the country you’re in, as different parts of the world use different parts of the world use different frequencies of current.

BUZZING/HUMMING OF A TRANSFORMER

Transformers hum for two main reasons: stray magnetic fields and magnetostriction. Magnetic fields cause the internal accessories of the transformer to vibrate at a frequency of either 50 or 60 Hz.

The other source of the electric hum produced by a transformer is magnetostriction. Magnetostriction occurs when a ferromagnetic material interacts with an alternating magnetic field, and consequently undergoes minute expansion and contraction.

Alternating magnetic field makes a ferromagnetic material expand and contract minutely.

When the iron core within the transformer coils expands or contracts (i.e., changes shape minutely) due to the magnetic effect of alternating current flowing through it, it produces a small amount of vibration. This is what makes the transformer produce that constant buzzing sound.

Transformers produce a slightly different kind of buzzing sound depending on whether they operate on 50 or 60 Hz frequency. (Photo Credit : Flicker)

These buzzing sounds of a transformer can be minimized by making certain design tweaks, but they cannot be completely eliminated. It should be noted that the intensity of those humming sounds is proportional to the applied voltage: the higher the applied voltage, the greater the ‘hum intensity’. This is why you may not always hear that humming sound from some transformers.

This section was all about transformers, but the explanation for the hum from overhead power lines is also quite interesting.

BUZZING/HUMMING OF HIGH POWER LINES

The sound that you hear from overhead power lines is due to a phenomenon called corona discharge. Corona discharge is an electrical discharge that occurs when a fluid (like air) surrounding an electrically-charged conductor becomes ionized.

In simple terms, it’s the noise that air (surrounding the power lines) makes as electricity jumps through it. Note that this is different from the mechanism that causes the electric hum in transformers.

Corona discharge usually occurs by itself in high-voltage systems, unless steps have been taken to limit the range of the electric field. In addition to producing a slow, buzzing sound, it also produces a bluish glow in the air surrounding power lines.

In fact, this phenomenon is not very different from a lightning bolt; you could say that it’s a miniature version of a lighting strike, only the latter produces a blinding flash of light (rather than a soft bluish glow) and a thundering boom (rather than a soft buzz).

HEAT SINK

As power transistor handle large currents, they always heat up during operation. Since transistor is a temperature dependent device, the heat generated must be dissipated to the surrounding in order to keep the temperature within permissible limits. Generally, the transistor is fixed on a metal sheet (usually aluminum) so that additional heat is transferred to the Aluminum sheet. The metal sheet that serves to dissipate the additional heat from the power transistor is known as heat sink.