Author: Lou Bloomfield

Why does breathing helium make our voices sound Mickey Mouse-ish? Is there anyth…

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Why does breathing helium make our voices sound Mickey Mouse-ish? Is there anything we can drink that will have the same effect for a longer period? – AP

The pitch of your voice is largely determined by the dimensions of your larynx. That’s why men, with their larger larynxes, generally have lower voices than women. While the sound of your voice originates in the vibrations of your vocal cords, string-shaped objects aren’t very good at emitting sound. Just as a violin employs a box to assist its strings in producing sound, you use your larynx to assist your vocal cords in producing sound. Which pitches your larynx produces well depends on its size and on the speed of sound. Both of these factors are important because the air itself vibrates and either decreasing the size of your larynx or allowing sound to move faster from one side of it to the other will raise the pitch of your voice. Because the speed of sound is much higher in helium (965 m/s) than it is in air (331 m/s), the pitch of your voice rises when you breathe in helium gas. However, as soon as the helium has left your lungs and is replaced by air, your voice returns to normal. Apart from breathing gases with high speeds of sound, there isn’t anything else that will work. You can’t live on pure helium gas, so the only way to sustain this effect would be to breath a helium/oxygen mixture instead of air. Some deep-sea divers do just that and their voices continue to sound “Mickey Mouse-ish” as long as they breathe this mixture.

Do sparks generated by Tesla coils shock humans? If not, why not? – AW

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Do sparks generated by Tesla coils shock humans? If not, why not? – AW

A Tesla coil is radio-frequency transformer that produces small currents of very high-energy electric charges. A radio frequency alternating current passes through the primary coil of this transformer and it induces a current in the secondary coil of the transformer. The frequency of the alternating current must be extremely high because there is no iron in the core of the transformer to store energy during a cycle, so that each cycle must be very brief. Because the alternating current flowing out of the secondary coil of the transformer has a very high frequency, it travels over the surface of a conductor, rather than through its center. Thus when you allow that current to pass through you, it goes along your skin and not through your body. As a result, you barely feel its passage except perhaps as surface heating (however, it can cause what is called an “RF burn” in some cases.) Also, the current from a typical Tesla coil is very small so it would barely be noticeable even if it went through your body.

Is there a touch sensor that can sense when you touch the body of a car? – AW

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Is there a touch sensor that can sense when you touch the body of a car? – AW

The same touch sensors that are used in “touch” lamps or some elevator buttons could be used to sense when you touch a car. A car is essentially insulated from the ground by its rubber wheels, so that when you touch it there is a tendency for electric charge to be transferred between the earth and the car through you. That’s why you may receive a shock when you touch a car on a cold winter day. Many electronic devices are capable of detecting this charge transfer (in fact, many of them would be damaged by such sudden and large charge transfers). So building a car touch sensor would be easy. Whether there is a commercial product that does this is another matter, and I am not sure of the answer.

How does a silencer work?

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How does a silencer work? — AWG, Karachi, Pakistan

When a bullet emerges from the barrel of a gun, the high-pressure gas that is propelling it from behind abruptly enters the atmosphere. This sudden burst of pressurized gas is like that released by an exploding firecracker and produces a loud “pop” sound. A silencer slows down this gas’s entry into the atmosphere. Before leaving the gun, the bullet passes through a series of air-filled chambers. The gas behind the bullet must enter each chamber, one at a time, and with each passage, its pressure and energy decrease. By the time the gas emerges from the last chamber, its pressure is low enough that it makes only a weak “whoosh” sound as it enters the atmosphere. This same technique is used by an automobile muffler. However, a silencer is only effective with low-velocity bullets. If the bullet itself travels faster than the speed of sound (331 m/s), it will create shock waves as soon as it enters the atmosphere and will generate its own explosion noise—miniature “sonic booms.”

There is an experiment involving grapes and microwaves that we found on the inte…

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There is an experiment involving grapes and microwaves that we found on the internet. If a grape is cut in half—with a piece of skin attached between the two halves—and it is then microwaves, sparks are produced. What is happening? — GB, Antioch, CA

This experiment is described in Fun with Grapes – A Case Study. While I haven’t tried it yet myself, I believe I know why it works. Grape juice is somewhat able to conduct electricity and the two halves of the grape are connected by a weak conducting path: the skin bridge. When the microwave oven is turned on, the microwaves not only heat the water in the grapes, they also push a few mobile electric charges back and forth through the skin bridge from one side of the grape to the other. This current releases energy as it passes through the narrow bridge and it heats the bridge extremely hot. The bridge soon catches fire and the electric current driven by the microwaves begins to pass through the flame. When current passes through a gas, it tends to ionize that gas (remove electrons from the gas atoms) so that the gas itself begins to conduct electricity. When current flows through atmospheric pressure air, it forms a brilliant arc. In this case, the arc that you see is powered by the microwaves as they push electric charges back and forth from one side of the grape to the other. An excellent set of movies showing this and other microwave oven experiments appears at http://www.physics.ohio-state.edu/~maarten/microwave/microwave.html.

Why don’t microwaves get stuck in the food we put in the microwave oven?

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Why don’t microwaves get stuck in the food we put in the microwave oven?

Microwaves are like light—both are electromagnetic waves and both move extremely quickly. While it is possible to trap a light wave briefly between two mirrors, that wave will eventually be absorbed or released. The same is true of a microwave. It’s almost impossible to trap a microwave for more than 1 second, even in very exotic enclosures, so you needn’t worry about them becoming trapped in food. The food simply absorbs them and turns their energy into thermal energy.

How does a hydrogen bomb work? How does it differ from the atomic bomb besides t…

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How does a hydrogen bomb work? How does it differ from the atomic bomb besides the simple difference of fusion and fission? — KS, Lake Oswego, OR

A hydrogen bomb uses the heat from a fission bomb (a uranium or plutonium bomb, sometimes called an atomic bomb) to cause hydrogen nuclei to collide and fuse, thereby releasing enormous amounts of energy. While a fission bomb can initiate its nuclear reactions at room temperature, fusion reactions won’t begin until the nuclei involved have been heated to enormous temperatures. That’s because the nuclei are all positively charged and repel one another strongly up until the moment they stick. Only at enormous temperatures (typically hundreds of millions of degrees) will the nuclei collide hard enough to stick and release their nuclear energy. A typical hydrogen bomb (also called a fusion bomb or thermonuclear bomb) uses a fission trigger to initiate fusion in a mixture of deuterium and tritium, the heavy isotopes of hydrogen. These neutron-rich isotopes fuse much more easily than normal hydrogen. Because deuterium and tritium are both gases, and because tritium is unstable and gradually decays into the light isotope of helium, some hydrogen bombs form the tritium during the explosion by exposing lithium nuclei to neutrons from the fission trigger. Thus the “fuel” for many thermonuclear bombs is actually lithium deuteride, which becomes a mixture of tritium and deuterium during the explosion and then becomes various helium nuclei through fusion.

Do you think it will ever be possible to build/create different atoms up to carb…

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Do you think it will ever be possible to build/create different atoms up to carbon or perhaps even gold (the alchemist’s dream)? You would have to use fusion, wouldn’t you? Would this be a good source of energy? — JB, Norman, OK

As you noted, this process of sticking together smaller atomic nuclei or nuclear fragments to form larger atomic nuclei is called fusion. Many smaller nuclei release energy when they grow via fusion, so long as the resulting nuclei are no larger than 56Fe (the nuclei of a normal iron atom). Above that size, energy is consumed in the process of sticking the nuclei together. So building carbon nuclei would release energy and building gold atoms would require energy. But while it’s possible to construct atomic nuclei up to carbon or even gold, it isn’t very practical. It’s very difficult to bring atomic nuclei close to one another because they are all positively charged and repel one another fiercely. Because the nuclear energy these nuclei release during fusion only emerges at the moment they actually touch, something must push them together for that to occur. The nuclei can be pushed together by (1) nuclear fission reactors, (2) particle accelerators, (3) thermonuclear weapons, (4) giant lasers, or (5) thermal fusion reactors. None of these systems is ready to synthesize large quantities of normal atoms in a cost effective manner (although nuclear fission reactors do produce useful quantities of radioactive isotopes) and none is ready to produce practical energy from fusion processes.

How fast does sound travel through the telephone? – T

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How fast does sound travel through the telephone? – T

When your voice travels through the telephone, it doesn’t travel as sound. Instead, the microphone of your telephone unit produces an electric current that represents the sound of your voice. From there on until it arrives at the earpiece of your friend’s telephone unit, your voice travels as an electromagnetic signal—either an electric current, a radio wave, or a light wave. Only when it reaches the earpiece is the electromagnetic signal used to recreate the sound itself. Since electromagnetic signals travel at or near the speed of light, your voice moves extremely quickly from your telephone unit to your friend’s telephone unit. It would be quite easy, for example, for a friend living a few miles away to tell you about a nearby explosion or thunderclap and then have you hear that explosion or thunderclap yourself. Your friend’s words would travel much more rapidly through the phone lines than the sound would travel over the countryside.

However, even the speed of light isn’t fast enough in some cases. Shortly after the break-up of AT&T, new long-distance carriers began to appear. Some of these companies used geosynchronous satellites to handle the long distance calls. Because these satellites sit about 22,300 miles above the earth’s equator, the travel time for radio waves to and from these satellites is a substantial fraction of a second. The delay between when you spoke and when your friend heard your voice was long enough that your friend might have begun talking, too. Those conversations were very awkward because you had to be very deliberate about starting and stopping your speech. You almost had to tell your friend when you were done talking so that they could begin. All modern long-distance calls are handled by surface links so that there is almost no delay, except perhaps when going to the other side of the earth.

Please explain how the different welding systems work, (Arc, TIG, MIG, and Oxy-A…

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Please explain how the different welding systems work, (Arc, TIG, MIG, and Oxy-Acet) and why some types work with certain metals (steel, aluminum, titanium, and cast iron) and others don’t? — DC, Ceder, MN

While I have very little experience welding myself, I can make a number of general observations about welding. All of the welding systems you mention are trying to join several pieces of metal by melting them together. In most cases, one of the pieces of metal is being used to form the joint and is sacrificed completely in the process (typically it’s a welding rod made of a special metal that’s good at forming a joint). How the melting and joining process proceeds depends on the welding system used.

An arc welder passes an electric current through the air from the pieces to be joined to a welding rod. The rod becomes so hot as the result of this arc that it melts and joins with the other pieces of metal, binding them together permanently. This scheme only works with relatively non-flammable metals such as steel. Aluminum or titanium will burst into flames when the arc starts. To joint these flammable metals, the arc has to be protected by a shroud of an inert gas such as argon or helium. TIG and MIG welding are based on this inert gas approach (the “IG” part of the names). In Tungsten-Inert-Gas (TIG) welding, an arc passes from the pieces being joined to a tungsten electrode. Tungsten has such as high melting point that it survives this arc and another piece of metal, the welding rod, is fed into the arc where it melts to form the joint. In Metal-Inert-Gas (MIG) welding, the arc passes from the pieces to a metal welding rod. This system resembles normal arc welding, in that the welding rod melts to form the joint, however now the arc is shrouded by a flow of inert gas so that there is no oxygen around to support combustion. Flammable metals can be welded with TIG or MIG welding and so can non-flammable metals.

As for oxygen-acetylene welding, here a very hot flame is used to heat the pieces involved to very high temperatures. A welding rod that melts at a slightly lower temperature than the pieces themselves is then used to join the pieces. The advantage to using this system is that it doesn’t pass a current through the pieces and doesn’t rely on their electric properties. The current of an arc welder could damage thin materials but an oxygen-acetylene flame should not (assuming they are relatively non-flammable metals). I’m sure that the metallurgical characteristics of the joints vary from system to system, but I can’t make any useful statements about this. For a more detailed discussion of when and where to use each technique, you’ll need a more experienced person than me.