sentence-transformers/squad huggingface dataset:
Passage: 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?

Question: What was the primary problem with early carbon filaments?

Question: What were the positive effects of the flashing process?

Question: What properties of graphite improved the filament?

Question: What are the effects of giving the filament a positive temperature coefficient?
Passage: 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?

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

Question: What were the major advantages of the tantalum light filament?

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

Question: When did GE cease production of the tantalum light filament?
Passage: 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?

Question: Who developed the ductile form of tungsten?

Question: When was the ductile form of tungsten invented?

Question: When was the tungsten filament introduced?

Question: What other materials were combined with tungsten?
Passage: 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?

Question: What is the advantage of a coiled-coil filament over a straight filament?

Question: What positive effects does a slower-evaporating filament enable?

Question: What is the typical diameter of the filament on a 60-watt bulb?
Passage: 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?

Question: Who discovered that inert gas could slow evaporation?

Question: Which gases are typically used in a light bulb?

Question: Which type of alloys can decrease "stairstep" irregularities in light bulb filaments?
Passage: 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?

Question: What affects the thermal conductivity of a gas?

Question: How does the molecular weight of a gas relate to thermal conductivity?

Question: Why is xenon gas not more widely used?

Question: What is the advantage of using inert gas in a light bulb?
Passage: 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?

Question: What is the typical goal for the life of a tungsten filament bulb?

Question: Which types of lamps may have particularly short lives?

Question: What is the typical tradeoff in light bulb design?
Passage: 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?

Question: What is the IEC guideline for an unacceptable level of light loss?

Question: What are the primary causes of light loss?

Question: Where in the bulb is evaporated tungsten deposited when inert gas is used?

Question: Where in the bulb is evaporated tungsten deposited when a vacuum is used?
Passage: 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?

Question: Why does water increase lamp darkening?

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

Question: How much water is necessary to result in this darkening affect?
Passage: 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?

Question: How does the halogen bulb decrease darkening over time?

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

Question: How does the size of a halogen bulb compare to an incandescent?

Question: What is the most common situation when a halogen bulb is used?
Passage: A variation of the incandescent lamp did not use a hot wire filament, but instead used an arc struck on a spherical bead electrode to produce heat. The electrode then became incandescent, with the arc contributing little to the light produced. Such lamps were used for projection or illumination for scientific instruments such as microscopes. These arc lamps ran on relatively low voltages and incorporated tungsten filaments to start ionization within the envelope. They provided the intense concentrated light of an arc lamp but were easier to operate. Developed around 1915, these lamps were displaced by mercury and xenon arc lamps.

Question: What did an alternate version of the incandescent lamp substitute for a wire filament?

Question: What was a common application for this type of bulb?

Question: When was this style of lamp developed?

Question: What displaced this style of lamp?
Passage: Incandescent lamps are nearly pure resistive loads with a power factor of 1. This means the actual power consumed (in watts) and the apparent power (in volt-amperes) are equal. Incandescent light bulbs are usually marketed according to the electrical power consumed. This is measured in watts and depends mainly on the resistance of the filament, which in turn depends mainly on the filament's length, thickness, and material. For two bulbs of the same voltage, type, color, and clarity, the higher-powered bulb gives more light.

Question: What does a power factor of 1 mean?

Question: What principally determines the wattage of an incandescent bulb?

Question: What determines the resistance of the filament?

Question: How close do incandescent lamps come to pure resistive loads?

Question: All other things being equal, how does wattage affect light emitted?
Passage: The actual resistance of the filament is temperature dependent. The cold resistance of tungsten-filament lamps is about 1/15 the hot-filament resistance when the lamp is operating. For example, a 100-watt, 120-volt lamp has a resistance of 144 ohms when lit, but the cold resistance is much lower (about 9.5 ohms). Since incandescent lamps are resistive loads, simple phase-control TRIAC dimmers can be used to control brightness. Electrical contacts may carry a "T" rating symbol indicating that they are designed to control circuits with the high inrush current characteristic of tungsten lamps. For a 100-watt, 120-volt general-service lamp, the current stabilizes in about 0.10 seconds, and the lamp reaches 90% of its full brightness after about 0.13 seconds.

Question: What determines the resistance of a filament?

Question: What does a "T" rating symbol on an electrical contact mean?

Question: How long does it take a typical 100-watt bulb to achieve 90% of its brightness?

Question: How does the cold resistance of tungsten filament lamps compare to the hot resistance?

Question: What is the resistance of a typical lit 100-watt incandescent bulb?
Passage: Incandescent light bulbs come in a range of shapes and sizes. The names of the shapes may be slightly different in some regions. Many of these shapes have a designation consisting of one or more letters followed by one or more numbers, e.g. A55 or PAR38. The letters represent the shape of the bulb. The numbers represent the maximum diameter, either in 1⁄8 of an inch, or in millimeters, depending on the shape and the region. For example, 63 mm reflectors are designated R63, but in the US, they are known as R20 (2.5 in). However, in both regions, a PAR38 reflector is known as PAR38.

Question: What do the letters identify in a bulb shape designation?

Question: What do the numbers identify in a bulb shape designation?

Question: Can the name of a certain bulb shape vary?

Question: What units are the bulb sizes measured in?
Passage: Very small lamps may have the filament support wires extended through the base of the lamp, and can be directly soldered to a printed circuit board for connections. Some reflector-type lamps include screw terminals for connection of wires. Most lamps have metal bases that fit in a socket to support the lamp and conduct current to the filament wires. In the late 19th century, manufacturers introduced a multitude of incompatible lamp bases. General Electric introduced standard base sizes for tungsten incandescent lamps under the Mazda trademark in 1909. This standard was soon adopted across the US, and the Mazda name was used by many manufacturers under license through 1945. Today most incandescent lamps for general lighting service use an Edison screw in candelabra, intermediate, or standard or mogul sizes, or double contact bayonet base. Technical standards for lamp bases include ANSI standard C81.67 and IEC standard 60061-1 for common commercial lamp sizes, to ensure interchangeablitity between different manufacturer's products. Bayonet base lamps are frequently used in automotive lamps to resist loosening due to vibration. A bipin base is often used for halogen or reflector lamps.

Question: Which company introduced standard base sizes for incandescent lamps?

Question: In what year were standard base sizes introduced for incandescent lamps?

Question: What are some common technical standards for lamp bases?

Question: What is the typical base type for automotive lamps?

Question: What is the typical base type for halogen lamps?
Passage: This means that a 5% reduction in operating voltage will more than double the life of the bulb, at the expense of reducing its light output by about 16%. This may be a very acceptable trade off for a light bulb that is in a difficult-to-access location (for example, traffic lights or fixtures hung from high ceilings). Long-life bulbs take advantage of this trade-off. Since the value of the electric power they consume is much more than the value of the lamp, general service lamps emphasize efficiency over long operating life. The objective is to minimize the cost of light, not the cost of lamps. Early bulbs had a life of up to 2500 hours, but in 1924 a cartel agreed to limit life to 1000 hours. When this was exposed in 1953, General Electric and other leading American manufacturers were banned from limiting the life.

Question: What level of voltage reduction is required to double the life of an incandescent bulb?

Question: When did light bulb manufacturers establish a cartel to limit bulb life?

Question: When did authorities break up the light bulb cartel?

Question: What was the artificially low limit on bulb life placed by the cartel?

Question: What is an example of a good application for a long-life bulb?
Passage: The relationships above are valid for only a few percent change of voltage around rated conditions, but they do indicate that a lamp operated at much lower than rated voltage could last for hundreds of times longer than at rated conditions, albeit with greatly reduced light output. The "Centennial Light" is a light bulb that is accepted by the Guinness Book of World Records as having been burning almost continuously at a fire station in Livermore, California, since 1901. However, the bulb emits the equivalent light of a four watt bulb. A similar story can be told of a 40-watt bulb in Texas that has been illuminated since 21 September 1908. It once resided in an opera house where notable celebrities stopped to take in its glow, and was moved to an area museum in 1977.

Question: When did the "Centennial Light" begin burning?

Question: How much light does the bulb emit?

Question: When did the long-lasting bulb in Texas begin continuing illumination?

Question: Where did the Texas bulb begin its life?
Passage: In flood lamps used for photographic lighting, the tradeoff is made in the other direction. Compared to general-service bulbs, for the same power, these bulbs produce far more light, and (more importantly) light at a higher color temperature, at the expense of greatly reduced life (which may be as short as two hours for a type P1 lamp). The upper temperature limit for the filament is the melting point of the metal. Tungsten is the metal with the highest melting point, 3,695 K (6,191 °F). A 50-hour-life projection bulb, for instance, is designed to operate only 50 °C (122 °F) below that melting point. Such a lamp may achieve up to 22 lumens per watt, compared with 17.5 for a 750-hour general service lamp.

Question: At what temperature does a typical 50-hour-life projection bulb operate?

Question: Which metal has the highest melting point?

Question: What is the typical life of a P1 lamp?

Question: How does the color temperature differ for photographic lighting?
Passage: Lamps designed for different voltages have different luminous efficacy. For example, a 100-watt, 120-volt lamp will produce about 17.1 lumens per watt. A lamp with the same rated lifetime but designed for 230 V would produce only around 12.8 lumens per watt, and a similar lamp designed for 30 volts (train lighting) would produce as much as 19.8 lumens per watt. Lower voltage lamps have a thicker filament, for the same power rating. They can run hotter for the same lifetime before the filament evaporates.

Question: How many lumens per watt does a typical 100-watt, 120-volt lamp produce?

Question: How many lumens per watt does a typical train light produce?

Question: How does filament size relate to voltage level?

Question: What is the effect of a thicker filament on bulb temperature?
Passage: In addressing the question of who invented the incandescent lamp, historians Robert Friedel and Paul Israel list 22 inventors of incandescent lamps prior to Joseph Swan and Thomas Edison. They conclude that Edison's version was able to outstrip the others because of a combination of three factors: an effective incandescent material, a higher vacuum than others were able to achieve (by use of the Sprengel pump) and a high resistance that made power distribution from a centralized source economically viable.

Question: What made power distribution economically viable in Edison's lamp?

Question: How many inventors came up with electric lamps before Thomas Edison?

Question: How did Edison achieve a higher vacuum than other inventors?

Question: Which historians wrote about the advantages of Edison's lamp over other early versions?
Passage: Physically, clothing serves many purposes: it can serve as protection from the elements, and can enhance safety during hazardous activities such as hiking and cooking. It protects the wearer from rough surfaces, rash-causing plants, insect bites, splinters, thorns and prickles by providing a barrier between the skin and the environment. Clothes can insulate against cold or hot conditions. Further, they can provide a hygienic barrier, keeping infectious and toxic materials away from the body. Clothing also provides protection from harmful UV radiation.

Question: What can clothing provide during hazardous activities?

Question: What type of surfaces can clothing protect from?

Question: What does clothing keep toxic materials away from?

Question: What can insulate against cold or hot conditions?

Question: What type of radiation can clothing provide some protection from?
Passage: There is no easy way to determine when clothing was first developed, but some information has been inferred by studying lice. The body louse specifically lives in clothing, and diverge from head lice about 107,000 years ago, suggesting that clothing existed at that time. Another theory is that modern humans are the only survivors of several species of primates who may have worn clothes and that clothing may have been used as long ago as 650 thousand years ago. Other louse-based estimates put the introduction of clothing at around 42,000–72,000 BP.

Question: What isn't it easy to determine about clothing?

Question: What organism has provided some information about the timeline of clothing?

Question: What habitat is the body louse specific to?

Question: What may modern humans be the only survivor of several species of?

Question: How many thousands of years ago may have clothing been worn?
Passage: The most obvious function of clothing is to improve the comfort of the wearer, by protecting the wearer from the elements. In hot climates, clothing provides protection from sunburn or wind damage, while in cold climates its thermal insulation properties are generally more important. Shelter usually reduces the functional need for clothing. For example, coats, hats, gloves, and other superficial layers are normally removed when entering a warm home, particularly if one is residing or sleeping there. Similarly, clothing has seasonal and regional aspects, so that thinner materials and fewer layers of clothing are generally worn in warmer seasons and regions than in colder ones.

Question: What obvious improvement does clothing bestow upon the wearer?

Question: In what type of climate does clothing protect against sunburn and wind damage?

Question: What property of clothing is important in cold climates?

Question: What has seasonal and regional aspects?

Question: What type of material tends to be worn in warmer seasons?