. At what temperature does paper burn? — KR
If the title of the book "Fahrenheit 451" is correct, then the temperature is 451° F (233° C). Actually, I'm sure that the ignition temperature depends on the exact type of paper.
. How hot is a match when it is ignited? Is the initial point of combustion hotter than when it is just burning? — TB, Excelsior, MN
You can usually judge the temperature of a hot object by its color—the brighter and whiter the light, the hotter the object. A candle flame has a temperature of roughly 1700° C while an incandescent light bulb has a temperature of about 2500° C. To my eye, a struck match briefly becomes brighter and whiter than a candle flame, so I would guess that its peak temperature is somewhere in the mid 2000° C range. Once the chemicals in the head have been used up, the flame temperature drops to about 1700° C.
. Does the creation of life and the theory of evolution violate the laws of thermodynamics? — BY, Liverpool, NY
While the laws of thermodynamics forbid an overall increase in the order of the universe and while life is an example of significant order, the laws of thermodynamics don't forbid some parts of the universe from becoming more orderly at the expense of other parts of the universe becoming less orderly. Living organisms are consumers of order and exporters of disorder—they derive their order by creating disorder elsewhere. You eat highly ordered chemicals in your food and you eliminate those chemicals in much more disordered forms latter on. You also emit heat, the most disordered form of energy. Thus thermodynamics has no problem with the ongoing existence of life; it simply requires that living organisms consume order and we are doing just that at a furious pace.
As for the creation of life, that could have been a random event and thermodynamics permits random events. Improbable events do occur—people win the lottery, lightning strikes twice, two snowflakes are occasionally alike—and the creation of life could have been one of those unlikely but not impossible events. Once the simplest organism had assembled itself by chance, it could then begin the process of consuming order and exporting disorder.
. How do fruit machines work? Do they operate on a fixed mathematical model which governs payouts using probability or are they totally random? — TS, Norfolk, UK
I assume that you are referring to the gambling machines that spin several wheels when you pull a lever and that pay you amounts that depend on the patterns of symbols that show on the faces of the wheels when they stop. While the final arrangement of symbols that appear on such a machine when it stops is entirely random, the patterns that pay and the amounts they pay are calculated to ensure a slight financial advantage for the house. The mathematics of probability is well developed for such gambling machines and it's relatively simple to determine what fraction of your money you should expect to lose if you play the game for a very long time. If you do play long enough to sample the full statistics of the game, you are certain to lose money. It's only if you play briefly that you can take advantage of statistical fluctuations to leave with more money than you had when you started.
. How much electric current is there in an automobile spark plug? — DG, Brooklyn, NY
Without measuring it directly, I would guess that the current passing through a spark plug during a spark is about 10 milliamperes. I base that guess both on a calculation—assuming sensible values for the energy, voltage, and duration of the spark—and on my experience with electric sparks. If I have a chance to measure the current directly—I have the equipment but not the time—I'll put a more specific value here.
. How does electricity get to my home?
The electricity you receive comes from a distant power plant. A generator in that power plant produces a substantial electric current of medium high voltage electric charge. This current is alternating, meaning that its direction of flow reverses many times a second—120 reversals per second or 60 full cycles of reversal (over and back) in the United States. This alternating electric current flows through the primary coil of wire in a huge transformer at the power plant, where it produces an intense alternating magnetic field. When a magnetic field changes with time, it produces an electric field and, in the transformer, this electric field pushes electric charges around a second coil of wire in the transformer, the secondary coil. The effect of this transformer is to transfer power from the current in the primary coil of the transformer to the current in the secondary coil of the transformer. Thus the generator's electric power moves along to the current passing through the secondary coil of the transformer. However, the secondary coil has far more turns of wire than the primary coil and this gives each charge passing through that coil far more energy than the charges had in the primary coil. Although the current passing through that secondary coil is relatively small, it acquires an enormous voltage by the time it leaves the secondary coil. The transformer has produced this high voltage power needed for efficient power transmission to a distant city.
This high voltage electric current passes through the countryside on high voltage transmission wires. The value of using a small current of high voltage charges is that wires waste power in proportion to the square of the electric current they are carrying. Since the current in the transmission wires is small, they waste relatively little power.
When this current reaches your town, it passes through a second transformer, which transfers its power to yet another electric current. This current is large and, because it passes through a coil that has few turns of wire, it acquires only a medium high voltage when it flows through the secondary coil of the new transformer. Electricity from this second transformer flows toward your neighborhood through medium high voltage wires. Finally, near your home there is a third and final transformer that extracts power from the medium high voltage current and transfers that power to a very large current that acquires a low voltage when it flows through the secondary coil of the final transformer. It is this very large current of low voltage charges that flows through appliances in your home and those of your neighbors. That final transformer is often visible as a large gray drum on a utility pole or a green box in someone's yard.
. How do windmills work to generate electricity? — KT, Aurora, Ontario
Windmills extract energy from the wind by rotating as the wind twists them. Whenever an object rotates in the same direction as the torque (the twist) being exerted on it, mechanical work is done on that object. In this case, wind exerts a torque on the windmill's blades and they rotating in the direction of that torque, so the wind is doing work on the blades. Work is the mechanical transfer of energy, so the wind is transferring some of its energy to the blades.
The blades don't keep this newly acquired energy. Instead, they do work on a generator. The generator, which consists of a rotating magnet that spins within stationary coils of wire, uses this energy to generate electricity. The amount of power that a windmill generates depends on the wind speed and the windmill's size, but large windmills can generate in excess of a million watts of electric power.
. Is it true that microwaves cause cancer?
I think that it's very unlikely that microwaves cause cancer. Microwaves are not ionizing radiation—they don't directly damage chemical bonds. Instead, they heat materials, particularly those containing water. As a result, they may cause damage to proteins in the same way that cooking damages proteins (and hardens egg protein, for example). But while such protein damage can easily cause cell death, I wouldn't expect it to cause the genetic damage associated with cancer.
. Why are any materials transparent? — MZ, Peligna, Italy
Because light is an electromagnetic wave, it is emitted and absorbed by electric charges. For an electric charge to emit light it must move—in fact, the charge must accelerate. For an electric charge to absorb light it must also move—it must also accelerate. However, there are many materials that do not have mobile electric charges. For example, while all electric insulators have electric charges in them, those electric charges can't move long distances. The electric charges in many electric insulators can't even move enough to absorb light and the light simply passes right through them. They are transparent.
. What is the difference between apparent weight and true weight?
Your true weight is caused by gravity—it is the force exerted on you by gravity; usually the earth's gravity. Your apparent weight is the sum of your true weight and a fictitious force associated with your acceleration. Whenever you accelerate, you experience what feels like a gravitational force in the direction opposite your acceleration. Thus when you accelerate to the left, you feel a gravity-like experience toward your right. It is this effect that seems to throw you to the right whenever the car you are riding in turns toward the left. In fact, this effect is caused by your own inertia—your own tendency to travel in a straight line at a constant speed. Your apparent weight can be quite different from your true weight. Perhaps the most striking example occurs on the loop-the-loop of a roller coaster. While your true weight remain downward throughout the ride, as it always is, your apparent weight actually becomes upward as you pass around the top of the loop-the-loop. You are accelerating downward so rapidly at the top of the loop that the experience you have is one of a gravity-like force that is pulling you skyward. Since the car you are riding in is invert and above you, you feel pressed into your seat even though the ground is in the other direction.