rajpurkar/squad huggingface dataset:
Title: Incandescent_light_bulb

Since incandescent light bulbs use more energy than alternatives such as CFLs and LED lamps, many governments have introduced measures to ban their use, by setting minimum efficacy standards higher than can be achieved by incandescent lamps. Measures to ban light bulbs have been implemented in the European Union, the United States, Russia, Brazil, Argentina, Canada and Australia, among others. In the Europe the EC has calculated that the ban contributes 5 to 10 billion euros to the economy and saves 40 TWh of electricity every year, translating in CO2 emission reductions of 15 million tonnes.

Question: Do incandescent light bulbs use more or less energy as compared to CFLs and LED lamps?
Answer: more

Question: How much does the incandescent light ban in Europe contribute to the economy each year?
Answer: 5 to 10 billion euros

Question: How much energy does the incandescent light ban in Europe save each year?
Answer: 40 TWh of electricity

Question: How much CO2 emissions does the incandescent light ban in Europe save each year?
Answer: 15 million tonnes

Question: How are laws written that bring about a ban of incandescent light bulbs?
Answer: by setting minimum efficacy standards higher than can be achieved by incandescent lamps
Title: Incandescent_light_bulb

Objections to banning the use of incandescent light bulbs include the higher initial cost of alternatives and lower quality of light of fluorescent lamps. Some people have concerns about the health effects of fluorescent lamps. However, even though they contain mercury, the environmental performance of CFLs is much better than that of light bulbs, mostly because they consume much less energy and therefore strongly reduce the environmental impact of power production. LED lamps are even more efficient, and are free of mercury. They are regarded as the best solution in terms of cost effectiveness and robustness.

Question: Is the environmental performance of CFLs better or worse than that of incandescents?
Answer: better

Question: Which type of light bulbs is considered most cost effective and robust?
Answer: LED lamps

Question: What are some objections to banning incandescent bulbs?
Answer: higher initial cost of alternatives and lower quality of light of fluorescent lamps

Question: What substance in CFL bulbs raises health concerns?
Answer: mercury

Question: Do CFLs consume more, less, or the same amount of energy as incandescent bulbs?
Answer: much less
Title: Incandescent_light_bulb

Prompted by legislation in various countries mandating increased bulb efficiency, new "hybrid" incandescent bulbs have been introduced by Philips. The "Halogena Energy Saver" incandescents can produce about 23 lm/W; about 30 percent more efficient than traditional incandescents, by using a reflective capsule to reflect formerly wasted infrared radiation back to the filament from which it can be re-emitted as visible light. This concept was pioneered by Duro-Test in 1980 with a commercial product that produced 29.8 lm/W. More advanced reflectors based on interference filters or photonic crystals can theoretically result in higher efficiency, up to a limit of about 270 lm/W (40% of the maximum efficacy possible). Laboratory proof-of-concept experiments have produced as much as 45 lm/W, approaching the efficacy of compact fluorescent bulbs.

Question: Which company introduced hybrid incandescent bulbs?
Answer: Philips

Question: How much more efficient are Halogena Energy Saver bulbs compared to incandescents?
Answer: 30 percent

Question: What company first marketed light bulbs using the reflective capsule technique to increase energy efficiency?
Answer: Duro-Test

Question: What is the theoretical maximum efficiency of reflective capsule bulbs?
Answer: 270 lm/W

Question: What is the maximum efficiency of reflective capsule bulbs as tested in labs?
Answer: 45 lm/W
Title: Incandescent_light_bulb

Incandescent light bulbs consist of an air-tight glass enclosure (the envelope, or bulb) with a filament of tungsten wire inside the bulb, through which an electric current is passed. Contact wires and a base with two (or more) conductors provide electrical connections to the filament. Incandescent light bulbs usually contain a stem or glass mount anchored to the bulb's base that allows the electrical contacts to run through the envelope without air or gas leaks. Small wires embedded in the stem in turn support the filament and its lead wires.

Question: What is the name of the air-tight glass enclosure in an incandescent bulb?
Answer: the envelope

Question: What is the filament made of?
Answer: tungsten wire

Question: How many conductors are present in the bulb's base?
Answer: two (or more)

Question: What prevents air or gas leaks from a light bulb?
Answer: a stem or glass mount anchored to the bulb's base

Question: What function do small wires in a light bulb's stem perform?
Answer: Small wires embedded in the stem in turn support the filament and its lead wires
Title: Incandescent_light_bulb

Most light bulbs have either clear or coated glass. The coated glass bulbs have a white powdery substance on the inside called kaolin. Kaolin, or kaolinite, is a white, chalky clay in a very fine powder form, that is blown in and electrostatically deposited on the interior of the bulb. It diffuses the light emitted from the filament, producing a more gentle and evenly distributed light. Manufacturers may add pigments to the kaolin to adjust the characteristics of the final light emitted from the bulb. Kaolin diffused bulbs are used extensively in interior lighting because of their comparatively gentle light. Other kinds of colored bulbs are also made, including the various colors used for "party bulbs", Christmas tree lights and other decorative lighting. These are created by coloring the glass with a dopant; which is often a metal like cobalt (blue) or chromium (green). Neodymium-containing glass is sometimes used to provide a more natural-appearing light.

Question: What is the powdery substance in coated glass light bulbs?
Answer: kaolin

Question: How is kaolin placed inside a light bulb?
Answer: blown in and electrostatically deposited

Question: What is the effect of a kaolin coating on the light cast?
Answer: a more gentle and evenly distributed light

Question: How are Christmas colored light bulbs created?
Answer: by coloring the glass with a dopant

Question: How does kaolin create a more gentle light?
Answer: It diffuses the light emitted from the filament
Title: Incandescent_light_bulb

Many arrangements of electrical contacts are used. Large lamps may have a screw base (one or more contacts at the tip, one at the shell) or a bayonet base (one or more contacts on the base, shell used as a contact or used only as a mechanical support). Some tubular lamps have an electrical contact at either end. Miniature lamps may have a wedge base and wire contacts, and some automotive and special purpose lamps have screw terminals for connection to wires. Contacts in the lamp socket allow the electric current to pass through the base to the filament. Power ratings for incandescent light bulbs range from about 0.1 watt to about 10,000 watts.

Question: What is the name for a base with one or more contacts at the tip and one at the shell?
Answer: screw base

Question: What is the name for a lamp base with one or more contacts on the base and a shell used as a contact or used only as a mechanical support?
Answer: bayonet base

Question: What is the purpose of contacts in the lamp socket?
Answer: allow the electric current to pass through the base to the filament

Question: What is the range of power ratings for incandescent bulbs?
Answer: 0.1 watt to about 10,000 watts

Question: Which types of lamps use screw terminals for connection to wires?
Answer: automotive and special purpose lamps
Title: Incandescent_light_bulb

The role of the gas is to prevent evaporation of the filament, without introducing significant heat losses. For these properties, chemical inertness and high atomic or molecular weight is desirable. The presence of gas molecules knocks the liberated tungsten atoms back to the filament, reducing its evaporation and allowing it to be operated at higher temperature without reducing its life (or, for operating at the same temperature, prolongs the filament life). It however introduces heat losses (and therefore efficiency loss) from the filament, by heat conduction and heat convection.

Question: What is a potential problem with the use of gas in a light bulb?
Answer: introduces heat losses (and therefore efficiency loss)

Question: What are the ideal chemical properties for the gas in a light bulb?
Answer: chemical inertness and high atomic or molecular weight

Question: What is the purpose of the gas in a light bulb?
Answer: to prevent evaporation of the filament, without introducing significant heat losses

Question: How do gases prevent evaporation of the filament?
Answer: The presence of gas molecules knocks the liberated tungsten atoms back to the filament
Title: Incandescent_light_bulb

In manufacturing the glass bulb, a type of "ribbon machine" is used. A continuous ribbon of glass is passed along a conveyor belt, heated in a furnace, and then blown by precisely aligned air nozzles through holes in the conveyor belt into molds. Thus the glass bulbs are created. After the bulbs are blown, and cooled, they are cut off the ribbon machine; a typical machine of this sort produces 50,000 bulbs per hour. The filament and its supports are assembled on a glass stem, which is fused to the bulb. The air is pumped out of the bulb, and the evacuation tube in the stem press is sealed by a flame. The bulb is then inserted into the lamp base, and the whole assembly tested.

Question: What type of machine manufactures glass light bulbs.
Answer: ribbon machine

Question: How many bulbs does the average ribbon machine produce per hour?
Answer: 50,000

Question: How is the filament attached to the bulb?
Answer: assembled on a glass stem, which is fused to the bulb

Question: How is the evacuation tube sealed?
Answer: by a flame

Question: What blows the glass bulbs into their characteristic shape?
Answer: precisely aligned air nozzles
Title: Incandescent_light_bulb

The first successful light bulb filaments were made of carbon (from carbonized paper or bamboo). Early carbon filaments had a negative temperature coefficient of resistance — as they got hotter, their electrical resistance decreased. This made the lamp sensitive to fluctuations in the power supply, since a small increase of voltage would cause the filament to heat up, reducing its resistance and causing it to draw even more power and heat even further. In the "flashing" process, carbon filaments were heated by current passing through them while in an evacuated vessel containing hydrocarbon vapor (usually gasoline). The carbon deposited on the filament by this treatment improved the uniformity and strength of filaments as well as their efficiency. A metallized or "graphitized" filament was first heated in a high-temperature oven before flashing and lamp assembly. This transformed the carbon into graphite which further strengthened and smoothed the filament. This also changed the filament to have a positive temperature coefficient, like a metallic conductor, and helped stabilize the lamp's power consumption, temperature and light output against minor variations in supply voltage.

Question: What material were the first light bulb filaments made from?
Answer: carbon

Question: What was the primary problem with early carbon filaments?
Answer: as they got hotter, their electrical resistance decreased

Question: What were the positive effects of the flashing process?
Answer: improved the uniformity and strength of filaments as well as their efficiency

Question: What properties of graphite improved the filament?
Answer: further strengthened and smoothed the filament

Question: What are the effects of giving the filament a positive temperature coefficient?
Answer: helped stabilize the lamp's power consumption, temperature and light output against minor variations in supply voltage
Title: Incandescent_light_bulb

In 1902, the Siemens company developed a tantalum lamp filament. These lamps were more efficient than even graphitized carbon filaments and could operate at higher temperatures. Since tantalum metal has a lower resistivity than carbon, the tantalum lamp filament was quite long and required multiple internal supports. The metal filament had the property of gradually shortening in use; the filaments were installed with large loops that tightened in use. This made lamps in use for several hundred hours quite fragile. Metal filaments had the property of breaking and re-welding, though this would usually decrease resistance and shorten the life of the filament. General Electric bought the rights to use tantalum filaments and produced them in the US until 1913.

Question: What company invented the tantalum light filament?
Answer: Siemens

Question: In what year was the tantalum light filament invented?
Answer: 1902

Question: What were the major advantages of the tantalum light filament?
Answer: These lamps were more efficient than even graphitized carbon filaments and could operate at higher temperatures.

Question: Who purchased the rights to the tantalum light filament from Siemens?
Answer: General Electric

Question: When did GE cease production of the tantalum light filament?
Answer: 1913
Title: Incandescent_light_bulb

In 1906, the tungsten filament was introduced. Tungsten metal was initially not available in a form that allowed it to be drawn into fine wires. Filaments made from sintered tungsten powder were quite fragile. By 1910, a process was developed by William D. Coolidge at General Electric for production of a ductile form of tungsten. The process required pressing tungsten powder into bars, then several steps of sintering, swaging, and then wire drawing. It was found that very pure tungsten formed filaments that sagged in use, and that a very small "doping" treatment with potassium, silicon, and aluminium oxides at the level of a few hundred parts per million greatly improved the life and durability of the tungsten filaments.

Question: What was the problem with manufacturing the tungsten filament?
Answer: Tungsten metal was initially not available in a form that allowed it to be drawn into fine wires.

Question: Who developed the ductile form of tungsten?
Answer: William D. Coolidge

Question: When was the ductile form of tungsten invented?
Answer: 1910

Question: When was the tungsten filament introduced?
Answer: 1906

Question: What other materials were combined with tungsten?
Answer: potassium, silicon, and aluminium oxides
Title: Incandescent_light_bulb

To improve the efficiency of the lamp, the filament usually consists of multiple coils of coiled fine wire, also known as a 'coiled coil'. For a 60-watt 120-volt lamp, the uncoiled length of the tungsten filament is usually 22.8 inches (580 mm), and the filament diameter is 0.0018 inches (0.046 mm). The advantage of the coiled coil is that evaporation of the tungsten filament is at the rate of a tungsten cylinder having a diameter equal to that of the coiled coil. The coiled-coil filament evaporates more slowly than a straight filament of the same surface area and light-emitting power. As a result, the filament can then run hotter, which results in a more efficient light source, while reducing the evaporation so that the filament will last longer than a straight filament at the same temperature.

Question: How long is a typical uncoiled tungsten filament for a 60-watt bulb?
Answer: 22.8 inches

Question: What is the advantage of a coiled-coil filament over a straight filament?
Answer: The coiled-coil filament evaporates more slowly

Question: What positive effects does a slower-evaporating filament enable?
Answer: more efficient light source

Question: What is the typical diameter of the filament on a 60-watt bulb?
Answer: 0.0018 inches
Title: Incandescent_light_bulb

One of the problems of the standard electric light bulb is filament notching due to evaporation of the filament. Small variations in resistivity along the filament cause "hot spots" to form at points of higher resistivity; a variation of diameter of only 1% will cause a 25% reduction in service life. These hot spots evaporate faster than the rest of the filament, which increases the resistance at that point—this creates a positive feedback that ends in the familiar tiny gap in an otherwise healthy-looking filament. Irving Langmuir found that an inert gas, instead of vacuum, would retard evaporation. General service incandescent light bulbs over about 25 watts in rating are now filled with a mixture of mostly argon and some nitrogen, or sometimes krypton. Lamps operated on direct current develop random stairstep irregularities on the filament surface which may cut lifespan in half compared to AC operation; different alloys of tungsten and rhenium can be used to counteract the effect.

Question: What is the negative effect of "hot spots" forming on the filament?
Answer: a variation of diameter of only 1% will cause a 25% reduction in service life

Question: Who discovered that inert gas could slow evaporation?
Answer: Irving Langmuir

Question: Which gases are typically used in a light bulb?
Answer: argon and some nitrogen, or sometimes krypton

Question: Which type of alloys can decrease "stairstep" irregularities in light bulb filaments?
Answer: alloys of tungsten and rhenium
Title: Incandescent_light_bulb

While inert gas reduces filament evaporation, it also conducts heat from the filament, thereby cooling the filament and reducing efficiency. At constant pressure and temperature, the thermal conductivity of a gas depends upon the molecular weight of the gas and the cross sectional area of the gas molecules. Higher molecular weight gasses have lower thermal conductivity, because both the molecular weight is higher and also the cross sectional area is higher. Xenon gas improves efficiency because of its high molecular weight, but is also more expensive, so its use is limited to smaller lamps.

Question: Why does inert gas reduce efficiency?
Answer: conducts heat from the filament, thereby cooling the filament

Question: What affects the thermal conductivity of a gas?
Answer: molecular weight of the gas and the cross sectional area of the gas molecules

Question: How does the molecular weight of a gas relate to thermal conductivity?
Answer: Higher molecular weight gasses have lower thermal conductivity

Question: Why is xenon gas not more widely used?
Answer: more expensive, so its use is limited to smaller lamps

Question: What is the advantage of using inert gas in a light bulb?
Answer: reduces filament evaporation
Title: Incandescent_light_bulb

During ordinary operation, the tungsten of the filament evaporates; hotter, more-efficient filaments evaporate faster. Because of this, the lifetime of a filament lamp is a trade-off between efficiency and longevity. The trade-off is typically set to provide a lifetime of several hundred to 2,000 hours for lamps used for general illumination. Theatrical, photographic, and projection lamps may have a useful life of only a few hours, trading life expectancy for high output in a compact form. Long-life general service lamps have lower efficiency but are used where the cost of changing the lamp is high compared to the value of energy used.

Question: What determines how fast a tungsten filament evaporates?
Answer: hotter, more-efficient filaments evaporate faster

Question: What is the typical goal for the life of a tungsten filament bulb?
Answer: several hundred to 2,000 hours

Question: Which types of lamps may have particularly short lives?
Answer: Theatrical, photographic, and projection lamps

Question: What is the typical tradeoff in light bulb design?
Answer: efficiency and longevity
Title: Incandescent_light_bulb

In a conventional lamp, the evaporated tungsten eventually condenses on the inner surface of the glass envelope, darkening it. For bulbs that contain a vacuum, the darkening is uniform across the entire surface of the envelope. When a filling of inert gas is used, the evaporated tungsten is carried in the thermal convection currents of the gas, depositing preferentially on the uppermost part of the envelope and blackening just that portion of the envelope. An incandescent lamp that gives 93% or less of its initial light output at 75% of its rated life is regarded as unsatisfactory, when tested according to IEC Publication 60064. Light loss is due to filament evaporation and bulb blackening. Study of the problem of bulb blackening led to the discovery of the Edison effect, thermionic emission and invention of the vacuum tube.

Question: What darkens a conventional bulb over its lifetime?
Answer: the evaporated tungsten eventually condenses on the inner surface of the glass envelope

Question: What is the IEC guideline for an unacceptable level of light loss?
Answer: An incandescent lamp that gives 93% or less of its initial light output at 75% of its rated life is regarded as unsatisfactory

Question: What are the primary causes of light loss?
Answer: Light loss is due to filament evaporation and bulb blackening

Question: Where in the bulb is evaporated tungsten deposited when inert gas is used?
Answer: on the uppermost part of the envelope

Question: Where in the bulb is evaporated tungsten deposited when a vacuum is used?
Answer: across the entire surface of the envelope
Title: Incandescent_light_bulb

A very small amount of water vapor inside a light bulb can significantly affect lamp darkening. Water vapor dissociates into hydrogen and oxygen at the hot filament. The oxygen attacks the tungsten metal, and the resulting tungsten oxide particles travel to cooler parts of the lamp. Hydrogen from water vapor reduces the oxide, reforming water vapor and continuing this water cycle. The equivalent of a drop of water distributed over 500,000 lamps will significantly increase darkening. Small amounts of substances such as zirconium are placed within the lamp as a getter to react with any oxygen that may bake out of the lamp components during operation.

Question: How does water vapor inside a light bulb affect lamp darkening?
Answer: significantly increase darkening

Question: Why does water increase lamp darkening?
Answer: The oxygen attacks the tungsten metal, and the resulting tungsten oxide particles travel to cooler parts of the lamp.

Question: What is an example of a substance that is added to light bulbs to reduce this effect?
Answer: zirconium

Question: How much water is necessary to result in this darkening affect?
Answer: The equivalent of a drop of water distributed over 500,000 lamps
Title: Incandescent_light_bulb

The halogen lamp reduces uneven evaporation of the filament and eliminates darkening of the envelope by filling the lamp with a halogen gas at low pressure, rather than an inert gas. The halogen cycle increases the lifetime of the bulb and prevents its darkening by redepositing tungsten from the inside of the bulb back onto the filament. The halogen lamp can operate its filament at a higher temperature than a standard gas filled lamp of similar power without loss of operating life. Such bulbs are much smaller than normal incandescent bulbs, and are widely used where intense illumination is needed in a limited space. Fiber-optic lamps for optical microscopy is one typical application.

Question: Does the halogen bulp increase, reduce, or have no effect on filament evaporation?
Answer: reduces

Question: How does the halogen bulb decrease darkening over time?
Answer: by redepositing tungsten from the inside of the bulb back onto the filament

Question: Does a halogen bulb operate at a higher or lower temperature than an incandescent?
Answer: higher

Question: How does the size of a halogen bulb compare to an incandescent?
Answer: bulbs are much smaller than normal incandescent bulbs

Question: What is the most common situation when a halogen bulb is used?
Answer: where intense illumination is needed in a limited space