How do conductors and insulators work?

Lou Bloomfield Leave a comment

How do conductors and insulators work? — SN, Beverly, MA

Because of the quantum physic that dominates the behaviors of tiny objects in our universe, electrons can’t travel in every path you can imagine; they can only travel in one of the paths that are allowed by quantum physics—paths that are called orbitals in atoms and levels in solids. When a material is assembled out of its constituent atoms, those atoms bring with them both their electrons and their quantum orbitals. These orbitals merge and blend as the atoms touch and they shift to form bands of levels in the resulting solid. The electrons in this solid end up traveling in the levels with the lowest energies. Because of the Pauli exclusion principle, only one indistinguishable electron can travel in each level. Since there are effectively two types of electrons, spin-up and spin-down, only two electrons can travel in each level of the solid.

In a conductor, there are many unused levels available within easy reach of the electrons. If the electrons have to begin moving toward the left, in order to carry an electric current, some of the electrons that are in right-heading levels can shift into empty left-heading levels in order to let that current flow. But in an insulator, all of the easily accessible levels are filled and the electrons can’t shift to other levels in order to carry current in a particular direction. While there are empty levels around, an electron would need a large increase in its energy to begin traveling in one of these empty levels. As a result, the electrons in an insulator can’t carry an electric current.

What role do gravity and inertia play in making a roller coaster work?

Lou Bloomfield Leave a comment

What role do gravity and inertia play in making a roller coaster work? — B

Gravity provides the energy source for a roller coaster and inertia is what keeps the roller coaster moving when the track is level or uphill. Once the roller coaster is at the top of the first hill and detaches from the lifting chain, the only energy it has is gravitational potential energy (and a little kinetic energy—the energy of motion). But once it begins to roll down the hill, its gravitational potential energy diminishes and its kinetic energy increases. Since kinetic energy is related to speed, they both increase together.

At the bottom of the first hill, the roller coaster has very little gravitational potential energy left, but it does have lots of kinetic energy. The roller coaster also keeps moving, despite the absence of gravitational potential energy. You can view its continued forward motion as either the result of having lots of kinetic energy or a consequence of having inertia. Inertia is a feature of everything in our universe—a tendency of all objects to keep doing what they’re doing. If an object is stationary, it tends to remain station. If an object was moving forward at a certain speed, it tends to keep moving forward at a certain speed. Inertia tends to keep the roller coaster moving forward along the track at a certain speed, even when nothing is pushing on the roller coaster. While the roller coaster will slow down as it rises up the next hill, its inertia keeps it moving forward.

Being born in the early 60’s, I grew up knowing that you could send a nuclear su…

Lou Bloomfield Leave a comment

Being born in the early 60’s, I grew up knowing that you could send a nuclear sub around the world on a chunk of uranium the size of a golf ball and that the half-life of plutonium was 38,000 years. So why does the world now have so much nuclear waste to get rid of? Why, if something has a half-life of many thousands of years, is it waste after only a few? — SG, Sydney, Australia

First, nuclear waste isn’t 100% radioactive atoms. Much of it is radioactively contaminated material—normal materials that contain enough radioactive atoms to be considered hazardous. Second, nuclear reactors don’t wait for radioactive materials to decay via spontaneous processes, the ones that are responsible for half-lives. Instead, they induce the radioactive decays using chain reactions. In a nuclear fission reactor, the spontaneous decay of one uranium or plutonium nucleus is used to induce decays in other uranium or plutonium nuclei. In this manner, huge fractions of the uranium or plutonium nuclei can be “used up” in only a few years. In fact, in a nuclear fission bomb, many or most of the uranium or plutonium nuclei are consumed in less than a millionth of a second because of these induced fissions. Half-life has almost nothing to do with a fission bomb. It becomes nuclear waste so fast you can’t imagine it.

How is glass made?

Lou Bloomfield Leave a comment

How is glass made?

Common window glass is made by melting a mixture of quartz sand (silicon dioxide), soda (sodium oxide), and lime (calcium oxide). The quartz is the network forming material that forms the basic structure of the glass. The soda makes it much easier to melt and work with—along with making the glass weaker and more temperature sensitive. The lime prevents the soda-rich glass from dissolving in water.

How do analog to digital converters change the analog input signal into a stream…

Lou Bloomfield Leave a comment

How do analog to digital converters change the analog input signal into a stream of numbers? — RME, Santa Monica, CA

A typical analog-to-digital converter (ADC) uses a process called “successive approximation” to find a binary number that accurately represents the voltage on an input wire. It samples the voltage on the input wire at one moment in time and then gradually constructs a binary number representing that voltage. The ADC tries various binary numbers and uses a digital-to-analog converter to form a voltage from each number. It compares the two voltages, the original and its approximation, to determine how close its current guess is to the correct value. With each successive approximation, it adds a bit a precision to its measurement so that after 16 approximations, it has a 16 bit number that accurately represents the voltage on the input wire.

For applications requiring even faster measurements, there are flash ADCs. These devices synthesize the entire range of possible voltages and then compare the input voltage directly with the complete collection of possible voltages. Since 8 binary bits can represent 256 possible numbers, an 8 bit flash ADC synthesizes 255 different voltages and makes 255 voltage comparisons simultaneously. It instantly determines where among the various voltages the input voltage falls and it reports this value in billionths of a second.

Why is the Hubble telescope in space rather than on earth?

Lou Bloomfield Leave a comment

Why is the Hubble telescope in space rather than on earth? — L

The earth’s atmosphere has poor optical properties that seriously diminish the resolving powers of even the finest earth-based telescopes. You can see these optical problems by watching the warm air rise above a radiator or hot pavement on a summer day. The little swirls and eddies of heated air distort the scenery beyond them. Earth-based telescopes have to look at the stars through several miles of swirling, inhomogeneous atmosphere and they struggle to compensate for the imaging problems this air causes. Most world-class telescopes are located on mountaintops, far from lighted urban centers and away from humidity and clouds. But even the sky above these mountaintop observatories causes problems. By putting Hubble in space, they got rid of all atmospheric problems—air turbulence, clouds, and nearby lighting. They also made it possible for Hubble to operate around the clock by eliminating the blue sky that blinds telescopes during the day.

How does a picture camera work?

Lou Bloomfield Leave a comment

How does a picture camera work? — HW, Ypsilanti, MI

A picture camera uses a lens to form a real image of a distant scene on the surface of a sheet of film. The lens bends rays of light so that all the light from a certain spot on the scene that passes through the lens comes together to a single point on the film. You can see this real image formation process with a magnifying glass. Just go into a darkened room with one window on a sunny day and hold the magnifying glass a few inches away from the wall opposite the window. You should see an inverted image of the window and the scene outside it projected on the wall. If you don’t move the lens toward or away from the wall until that image forms. Everything else about a camera is just helping that lens form its image on the film in a controlled fashion. The camera’s shutter limits the amount of time that light has to form this image. The focus controls make sure that light from the object you are interested in forms a sharp image on the film and doesn’t appear blurry.

What is zero point energy?

Lou Bloomfield Leave a comment

What is zero point energy? — AWG, Karachi, Pakistan

All objects in our universe have wave-like characteristics that manifest themselves in certain circumstances. These wave-like characteristics become more significant as objects become smaller. Their wave-like characteristics allow small particles to have ill-defined locations. To understand what I mean by “ill-defined locations”, consider a wave on the surface of a lake. There is no one point at which this wave is located—it is located over a region of the water’s surface. Waves don’t have well defined locations. Similarly, if you observe an electron, which is really a wave, there is no one point at which that electron is located—it is located over a region of space. Because of the detailed relationships between wavelength, frequency, and energy, the smaller the region of space in which the electron-wave can be found, the higher its energy must be. Thus an electron that is localized at all—that is known to be within a certain region of space—must have a certain minimum energy, even if it is stationary. This minimum energy is called zero point energy and it is a consequence of trying to localize the particle within a certain region of space. Since the zero point energy is a base level and can’t be reduced, you can’t use zero point energy to do anything useful. It’s just there.

How does a black light work?

Lou Bloomfield Leave a comment

How does a black light work? — JLM, Kettering, OH

I think that most black lights are gas discharge lamps that resemble normal fluorescent lamps. However, while a normal fluorescent light uses fluorescent phosphors to convert the ultraviolet light produced by its mercury discharge into visible light, a black light allows that ultraviolet light to emerge from the lamp unchanged. The ultraviolet light from a mercury discharge has too short a wavelength to be useful or safe as artistic black light, so other gases are likely to be used. The lamps are probably filtered so that they emit relatively little visible light or short wavelength ultraviolet light.

How do the spectrums of different light sources differ? For example, when you lo…

Lou Bloomfield Leave a comment

How do the spectrums of different light sources differ? For example, when you look at an incandescent bulb through a spectroscope, do you see colors other than what you see when you look at a fluorescent bulb? — EC, Tokyo, Japan

The spectrum of light from an incandescent bulb is what is known as a blackbody thermal spectrum—the light produced by a hot object. A blackbody spectrum is relatively featureless—you can’t even tell what material is producing the light; only what temperature it has. All the wavelengths of light are present in thermal radiation and their intensities vary smoothly with wavelength. For the filament temperature of a normal incandescent bulb, the reds are brighter than the greens and the blues are rather weak.

A fluorescent bulb pieces together white light out of several separate colored lights. The spectrum of light from a fluorescent lamp is not simple or featureless—many wavelengths are essentially missing and the intensities of the remaining wavelengths don’t vary smoothly with wavelength. Viewed through a spectroscope, the light from a fluorescent light has many bright bands of color interspersed with relatively dark bands.