. How does an integrated circuit perform computations? I know that it has transistors embedded into it, but how can a circuit of semiconductors be used for multiplication? — DF, Marina Del Rey, California
The transistors used in digital integrated circuits, including microprocessors, act primarily as electronically controlled switches. These transistor switches permit the electric charge on or electric current in one wire to control the electric charge on or current in another wire. In digital electronics, a wire's charge or current state is used to represent a single binary digit—either a 1 or a 0. By combining transistors in modestly complicated arrangements, the states of several wires together can control the states of several other wires. This increased complexity allows for simple functions such as binary addition to be performed—for example, the charges on two wires can be used to control the charges on two other wires so that the charges on the second pair of wires represent the single binary sum of the two individual numbers represented by charges on the first pair of wires. More complicated adders can be assembled from more transistors and finally multipliers can be assembled from a collection of adders. Overall, it only takes a few arrangements of electrically controlled switches to form the primitive elements from which incredibly complicated digital processors can be built.
. When two identical items are cooked, one with a microwave oven and the other on the stove, which will cool faster? — CR
If the distributions of temperatures inside the items were the same after cooking, they would cool at the same rate. However, a microwave oven tends to cook relatively evenly throughout the food while the stove tends to cook from the outside of the food inward. That means that food cooked in a microwave oven tends to have more thermal energy near its center than food cooked on a stove, even when those foods contain the same total amount of thermal energy. Since foods lose heat through their surfaces, the extra thermal energy in the food cook by microwave will take longer to flow out to the surface of the food and from there to its surroundings. All else being equal, I would expect the food cooked in the microwave oven to cool slightly slower than the food cooked on the stovetop.
. Do the resonant frequencies of the elements change as the magnetic fields they reside in change? Can an element such as iron be made to resonate at the magnetic field strength of the earth? — JP, Blakeslee, PA
The terms "resonant" and "resonate" are general expressions that refer to repetitive motions or actions that occur spontaneously within a system. Elements exhibit many different resonant behaviors in different situations, so I must pick an appropriate resonant behavior in order to answer your question.
The best choice I can think of is nuclear magnetic resonance (NMR)—an effect that involves the flipping of an atomic nucleus's magnetic poles. Most atomic nuclei—the massive positively charged nuggets at the centers of atoms—are magnetic. When you put an atom with a magnetic nucleus in a magnetic field, the atom acquires a certain amount of potential energy that depends on whether that magnetic nucleus is aligned with the magnetic field or not. The extent to which the atom's nucleus is aligned with the field can be changed by exposing it to an electromagnetic wave of the right frequency. This electromagnetic wave provides or absorbs the required energy to allow the nucleus's magnetization to flip. The nucleus exhibits a resonance in response to the correct electromagnetic wave—a phenomenon called "nuclear magnetic resonance." This frequency at which this resonance occurs depends on the nucleus, on the magnetic field, and on the magnetic environment of the nucleus. The resonance occurs for any magnetic nucleus, in any field, but how interesting or useful the resonance is depends on the situation. So the answers to both questions are yes, but that doesn't mean the effects are important.
. How do neon lights work? — MT, Cement City, MI
A neon light uses a very high voltage to propel an electric current through a low-density gas of neon atoms. These neon atoms are trapped inside a glass tube and the current passes between two metal electrodes at opposite ends of that tube. A high voltage power supply—typically a neon sign transformer—pumps a large number of negative charges onto one electrode and a large number of positive charges onto the other electrode. Because like charges repel while opposite charges attract, there are strong forces pushing the charges from one electrode toward those on the other electrode. Eventually, charges at the two ends of the tube begin to leap off the electrodes and into the neon gas so that they can flow toward one another. Current begins to flow through the tube. As the charges move through the gas, they frequently collide with neon atoms and occasionally transfer some of their energies to those neon atoms. During such an energy transfer, an electron in the neon atom shifts from its normal orbital to a higher energy orbital in which the electron doesn't normally travel. The electron soon returns to its normal orbital and releases a particle of light—a photon—in the process. Since the most common orbital shift in an excited neon atom releases a particle of red light, a neon light emits a bright, reddish glow.
. Is it possible that time is not just an abstraction but also a sort of resonant force that can be contained and manipulated within a controlled environment? — SK, Cape Town, South Africa
Time is a dimension, much like the three spatial dimensions. Objects and events are located in time, just as they are located in space. Because time is part of the framework in which objects and events exist, and not an object or an event, time can't be manipulated easily. So the short answer to your question is no, time can't be contained or manipulated. However, time and space are related and how we perceive the two depends on our velocity—the special theory of relativity. Moreover, time and space can be warped by the presence of mass/energy—the general theory of relativity. Still, the dream of playing with space-time like it was taffy that could be stretch, bent, and folded at will is just that, a dream. It takes an enormous concentration of mass/energy to cause even the most barely perceptible deformations of space-time and even the effects of celestial objects on space-time are limited. Finally, about the expression "resonant force": a resonance is a motion or action that spontaneously follows a repetitive cycle while a force is a push or a pull, an influence that causes something to accelerate. Thus, the expression "resonant force" is interesting sounding jargon but it doesn't have any meaning.
. Why do we have time? — KD, McMinnville, Oregon
Time is the fourth dimension, similar to but not equivalent to the three spatial dimensions. With four dimensions in our universe, we need four values to specify the exact location of each event—three values that specify that event's location in space and one value that specifies its location in time. Space and time are intimately related so that we perceive time in terms of space and space in terms of time. For example, you sense the distance of a remote city by how long it would take you to get there. Similarly, you sense the large separation between two moments in time by how far you could travel between those two moments. But as to "why we have time," I can only answer that it's part of the nature of our universe.
. Does a device that has radio waves and uses ozone and negative ions have the ability to clean the air in my home? — KTR, Halifax, Nova Scotia
There are many simple electronic devices that claim to clean the air in your home by making negative ions and ozone (if they involve any radio waves, it's a minor side effect of their internal electronics). The claim is accurate—they do make both ozone and negative ions, and they do clean the air in your home. However, that's not the whole story. First, ozone may have the "fresh" smell that occurs after a thunderstorm (a potent producer of ozone), but ozone is a powerful oxidizing agent and chemical irritant that's considered an environmental pollutant rather than a charming scent. The manufacturers are taking a nuisance effect and touting it as a "valuable feature." Second, the negative charges emitted by these electronic devices attach themselves to dust, ash, pollen, and smoke particles and cause those particles to bind themselves to your walls and furniture. The air really does become cleaner, but every surface in your home becomes dirtier as a result.
If you're seriously interested in cleaning the air in your home, you are probably better off with a full electrostatic air cleaner. Small home versions of this common industrial workhorse are easy to obtain at a local heating and air conditioning store. Properly designed machines use positive ions to avoid producing ozone and provide a negatively charged surface for the positively charged dirt to stick to so that it doesn't deposit itself on your walls.
. I recently place a green tomato in the microwave oven. I forgot to turn on the microwave and in the morning the tomato was ripe. Can you explain this? — KH
No. When a microwave oven is off, the cooking chamber contains nothing special at all—just some trapped air and perhaps a little light that enters through the window. Even when it is operating, a microwave oven never produces any ionizing (high energy) radiation so there are no long-term effects such as radioactivity present in the cooking chamber when the oven is off. The tomato was simply sitting in a sealed metal box overnight. Since some fruits ripen faster in sealed environments, perhaps that accounts for your observation.
. Can light be bent by electric fields, magnetic fields, and gravity fields? If so, can these fields be made to make light travel in a circle? — RS
Light consists of electromagnetic waves, meaning that it is composed of electric and magnetic fields. While light isn't affected by other electric or magnetic fields, it is affected by gravitational fields. Like everything else in our universe, light falls when exposed to gravity. However, because light travels so fast, it's very hard to detect that it falls. The first observation of light falling in a gravitational field was made during a total eclipse in 1919 and served as dramatic confirmation of the predictions of Einstein's general theory of relativity. As for light traveling in a circle, this can occur near the surface of a black hole. When light traveling tangent to the surface of the black hole falls at just the right rate, it will orbit the black hole indefinitely.
. How does cathodic protection work? — MM, Dominican Republic
The rusting of damp steel is an electrochemical reaction in which iron atoms in the steel are converted into positively charged iron ions (Fe2+
) in the water. However, each iron atom that becomes an ion releases two negatively charged electrons and rusting can only continue if there is a suitable destination for these electrons. Normally, the electrons pass through the steel metal and are used together with oxygen molecules to form negatively charged hydroxide ions (OH-
) in the water. Overall, the rate at which the steel rusts is limited by how quickly hydroxide ions can be formed to use up the electrons.
Cathodic protection is a scheme in which a piece of reactive metal, typically magnesium, is connected to the steel to form an electrochemical cell. Magnesium ions (Mg2+) form more easily than iron ions and enough electrons are given up by the magnesium atoms as they become positive ions to completely dominate the hydroxide ion formation process. With nowhere for their electrons to go, the iron atoms can't become iron ions and rusting can't proceed. As long as the magnesium metal, often called the "sacrificial anode", remains intact and connected to the steel, the steel won't rust significantly.
As an alternative to this approach, some companies use a power supply to pump negative charges onto the steel to prevent it from rusting. Pipeline companies often do this and that action has led to some interesting complications: metal objects that are brought into contact with such a pipeline can be protected against rusting as well. For example, when people chained their bicycles to protected pipelines, the bicycles became part of the protected materials. This may have been good for the bicycles, but it confused the pipeline companies who found that they needed to pump extra charge onto the pipelines to handle the increased load. It was particularly bad when the bicycles accidentally grounded the pipelines and allowed the negative charges to escape.