"There does not exist a category of science to which one can give the name applied science. There are sciences and the application of sciences, bound together as the fruit of the tree which bears it." -Louis Pasteur (1822-1895)
Today, we generally think of technology in terms of the growth of machines during the Industrial Revolution—locomotives, hydroelectric power plants, manufacturing processes—or, more recently, the computer-driven advances of the past half century—personal computers, cell phones, medical imaging. In a broader sense, though, technology refers to anything humans do in order to modify nature to meet their needs. The transformation of a large stick into a club, learning to control which plants grew in a particular place, and the invention of the wheel were all momentous advances in technology.
Another way to look at technology is as the combination of science and engineering. Science is the process of learning about the natural world, and engineering is a process of solving problems. Technology is the application of scientific knowledge to design solutions.
How does a microwave oven heat food?
Until the late twentieth century, an oven always heated food by surrounding it with hot air. A gas flame, glowing electrical heating element, or even a wood fire heated a chamber in which the food was placed. Heat was transferred from the hot air into the food. When the microwave oven was introduced, it cooked in a completely different way. How does a microwave oven work?
Microwave ovens use electromagnetic radiation, related to light or radio waves, at just the right frequency to interact with water molecules. The magnetron inside the oven emits radiation at microwave frequencies in the same way that a radio tower emits radio waves. The cabinet is designed to reflect the waves back and forth inside the heating compartment until their energy is absorbed by the food.
That’s why it is not a good idea to operate the microwave oven with nothing inside it. The microwave radiation is trapped and its energy increases, eventually damaging the magnetron itself.
Microwaves pass through glass and plastic without being absorbed or heating the material. There is a metal plate inside the glass door that reflects the radiation back toward the food in the oven. Small holes in the plate allow light to pass through so that you can watch the food as it cooks. The wavelengths of the microwaves are much longer than the diameter of the holes, however, so they cannot pass through it to the window.
As the waves pass through the food in the microwave, they create cycles of electric and magnetic fields that change direction 2.45 billion times per second. The regular changes in this field cause water molecules, which are polar, to rotate. As the molecules rotate faster and faster, they bump into the molecules around them and transfer energy that causes those molecules to move faster—and become hotter.
Microwaves do not interact with most molecules, so you cannot cook very dry foods in a microwave oven unless you add water. For example, dry rice or pasta is not cooked unless some water is added. Popcorn, however, is great microwave food because of the water stored inside each kernel.
You may have heard that microwave ovens cook food from the inside toward the outside. This is not true. Energy is absorbed by water molecules in the outside inch or so and heat is transferred inward as molecules bump into one another. When you defrost food in a microwave oven, the power comes on for a few seconds and then turns off for several seconds. This allows some of the energy to transfer inwards before more heat is added.
How do light-emitting diodes work?
If you compare a flashlight that uses several light-emitting diodes to a flashlight with an incandescent bulb, you will find the LED flashlight is much brighter. Also, the bulb of the incandescent light becomes very hot over time while the LED stays cool. The battery lasts much longer as well. Why is an LED more efficient than a light bulb?
A diode is an electronic component that allows current to pass in only one direction. Diodes are often used to convert alternating current to direct current, to convert electrical energy into electromagnetic energy, or as on-off switches in electronic circuits.
LEDs are diodes that emit light when a sufficient voltage is applied across them. The main part of the LED is a semiconductor chip (usually made of a combination of gallium, arsenic, and aluminum) that has two parts that are separated by a junction. One side of the junction holds a negative charge and the other side holds a positive charge. The junction is a barrier that prevents electrons from moving from the negative to the positive regions.
When the diode is connected to a power source, a voltage is applied across the junction, and electrons jump from the negative side to the positive side. When the negative charge (electron) and the positive charge (atom that has lost an electron) combine, the electron moves to a low-energy state and releases energy as a photon of light. As a result, electrical potential energy from the battery or other power source is converted into electromagnetic energy. The color of the light emitted is a function of the exact materials used to make the semiconductor.
Because LEDs operate without generating heat and do not have a filament to burn out, they last much longer than regular light bulbs. Until recently, LEDs were fairly expensive to build compared to other light sources. However, as less expensive semiconductors have been developed, LEDs are used for more applications.
They have been common as indicators to show when an appliance is turned on or off for some time. Other uses include tail lights for cars and trucks, flashlights, and even the flashing lights in some children’s shoes. They are also used in many traffic lights, where reliability is critical and maintenance is expensive. Although they are generally more expensive to buy, LED traffic lights function for many years without a need to replace the bulbs, and they consume significantly less power. For these reasons, many municipalities have begun to replace their old traffic lights with LEDs. Once all traffic lights have been replaced, the savings in electricity will be about $200 million per year in the United States alone.
In fact, LEDs have already become so common that we often don’t even notice them. Try turning off the lights in a room with a computer, router, printer, television, and several other electronic devices, and you are likely to notice that you are surrounded by LED lights.
How can a remote control turn a television on and off across a room?
Once upon a time, in the distant past, if you wanted to watch a different television program, you had to walk to the set and turn a dial. Today, however, you control your television, stereo, DVD player, and even the ceiling fan with the touch of a button on the remote. How do remote control devices work?
A television remote control (or any of the other remotes sitting on your coffee table) emits a signal from a diode that is similar to an LED. The wavelength emitted by a diode depends on the change in energy when an electron combines with a positively charged ion. Remote control devices use diodes made of silicon, in which the energy change is less than that of a light-emitting diode. Silicon diodes emit radiation in infrared wavelengths.
Because the radiation is in the infrared range, you don’t see it. But a receiver in the television set does. If you place something, or someone, between the controller and the receiver, it does not work because the signal is blocked.
There is always infrared light around, so the set also needs some way to recognize the signal from the remote. The signal is a series of flashes. A digital signal can be sent by switching back and forth between two frequencies. Part of the signal is set to identify the correct device (allowing a single remote to control several pieces of equipment) and part of the signal defines the desired action.
A restaurant pager operates on a principle similar to that of the TV remote. However, the pager must be usable even if a person is not in an unobstructed line from the transmitter. To solve this problem, the pager uses radio waves, which have a much longer wavelength than infrared radiation. Radio waves are able to pass through walls and reach the pager, even in the bar.
How does a smoke alarm detect smoke?
The first sign of a fire is often smoke, small particles of partially burned material floating in the air. Smoke detectors provide early warning of danger, saving many lives every year. During the night, as people sleep, a loud alarm is much more likely to wake them up than the smell of smoke. How does the detector find smoke in the air, often before it is noticeable by any other means?
There are two types of smoke detectors commonly used in homes: photoelectric and ionization. Some smoke alarms combine the two because their sensitivities to different types of smoke vary.
A photoelectric detector uses a beam of infrared light from an LED inside a tube. A lens focuses the light into a beam which passes through the tube. A light sensor is placed at a 90° angle to the beam. Normally the light passes from one end of the tube to the other, and the sensor does not detect any of the light coming from the source. However, when particles of smoke enter the detector, they scatter the light from the beam. When some of the scattered light strikes the sensor, it sets off the alarm.
Ionization smoke detectors use about ‘/5,000 of a gram of a radioactive isotope, americium-241, which emits alpha radiation (a particle identical to a helium nucleus). Every second, this amount of americium-241 emits about 37 billion particles. This sounds like a lot, but it is not enough to create a health hazard.
Although ionization detectors contain radioactive materials, they do not present a health hazard. The amount of radiation is very small, even though the absolute number of particles emitted seems very large. Alpha radiation is blocked by material as thin as a sheet of paper, so it cannot penetrate the plastic housing of the detector. In fact, alpha radiation is blocked by an inch or two of air. Generally, materials that emit only alpha radiation are not hazardous unless they are inhaled.
On opposite sides of the ionization chamber of the detector, there are electrically charged metal plates, positive on one side and negative on the other. A battery connected to the two plates maintains these charges. When the alpha particles strike oxygen or nitrogen molecules in the air, the collisions knock electrons away from atoms of the molecules. This makes two charged particles, a positively charged molecule and a negatively charged electron. These charged particles are attracted to the oppositely charged plates so they move toward them, causing an electric current to flow.
When smoke enters the chamber, it absorbs the alpha particles and disrupts the ionization of air. When a sensor detects a drop in the current, it sets off the alarm.
Both types of smoke detectors are very effective, but there are some differences in sensitivity. Optical detectors are particularly sensitive to very smoky fires, such as mattress fires and slowly smoldering fires. These fires produce thick smoke with large particles and have a greater tendency to scatter light. Ionization detectors respond more quickly to fast-burning flames, which produce smaller particles in greater numbers. Ionization detectors have an additional built-in security feature. If the battery begins to fail, the charge between the plates drops. This reduces the current and causes the alarm to sound a warning signal.
Fast Facts
A smoke detector only detects particles that form during combustion, so it provides no warning of carbon monoxide, a poisonous gas caused by incomplete combustion. Homes that are heated by burning natural gas, oil, wood, or other fuels should either have a separate carbon monoxide detector or a smoke detector that also integrates a carbon monoxide detector.
How does my GPS receiver know where I am?
Ancient navigators used the position of the stars to determine their locations. Later, sailors far from land calculated their location by using a compass and the sun. Today we can drive from one place to another, navigating with a GPS receiver that continually updates our current location and the route to our destination. How does this system determine locations?
In principle, global positioning systems (GPS) are fairly simple devices. Global positioning uses satellites orbiting Earth as reference points. The satellites constantly send out radio signals that are detected by receivers on the ground (or in ships or airplanes). These signals include information about the satellite’s location and the exact time.
The receiver uses a clock to measure the amount of time needed for the radio signal, traveling at 186,000 miles per second, to reach it. Based on that time, it can calculate the distance to the satellite, which means it is somewhere on a sphere of points that are all the same distance from the satellite. A signal from a second satellite narrows the possible locations to a circle. Then a third signal leaves only two possible locations for the receiver. The surface of Earth is the fourth sphere, narrowing the choices to one possible point. The system includes at least 24 operating satellites at all times so that there are always three or more satellites with a line of sight to the receiver.
A nanosecond is one billionth of a second. In the international system of units, the prefix nano-represents one billionth.
In practice, the process is a bit more complicated. An accurate calculation requires an accurate measurement of time with precision of a few hundred nanoseconds or better. This type of precision is only obtainable with an atomic clock, costing many tens of thousands of dollars. Since that is beyond the range of most purchasers of GPS receivers, it requires some mathematical tricks.
Each satellite does carry an atomic clock (and at least one backup), so the times are synchronized on the satellites. The receiver first calculates the real time from these signals, and then calculates the distance.
How accurate is a GPS measurement? Most receivers can pinpoint your location to within about 30 feet. If you can pick up more satellites, your positioning improves, perhaps to within 10 to 15 feet of your actual location. Finally, in some places, ground-based transmitters provide an additional location. Using one of these signals, in addition to the satellites, allows the receiver to calculate a position within a few feet, close enough to tell which corner of an intersection you are standing on.
Why are atomic clocks so accurate?
In the early eighteenth century, British clockmaker John Harrison won a fortune from the British Parliament for developing a clock that was accurate to within ‘/3 of a second per day, far better than any other clock of the time. Accurate timekeeping was an essential part of determining latitude, making Harrison’s timepiece invaluable to the British navy. Accurate timekeeping is just as important today—for telecommunications, global positioning, space exploration, and even securities trading. However, fractions of a second have now become massive errors. Atomic clocks provide accuracy to billionths of a second. How are these clocks so accurate?
All clocks depend on a vibration or oscillation—a repeating motion that occurs at a predictable frequency. From ancient times many different motions have been used to record time. The rotation of Earth on its axis and its revolution around the sun were the earliest periodic motions used for keeping time. Later clocks were based on the flow of sand through a constriction, the periodic swing of a pendulum, and the rhythmic swing of a spring-powered balance wheel. Modern quartz watches use the constant vibrations of a quartz crystal exposed to an electric current to measure the passage of time.
Every cycle used to run a clock has some variability. A pendulum clock may lose a few minutes and have to be reset each day. Even an inexpensive quartz watch can gain or lose a second per day. Atomic clocks, however, measure time within about 2 nanoseconds per day, or one second in about 1.4 million years.
Atomic clocks base their timekeeping on vibrations within atoms, which are the most consistent cycles known. Most atomic clocks use cesium atoms in an excited state, that is, in which an electron is at an energy level higher than its ground state. When the electron loses energy, it emits electromagnetic energy in the microwave frequency. Because the frequency of this oscillation is exactly the same for every cesium atom, a clock can be tuned using the frequency of radiation that matches the oscillation of the electron around the nucleus of the cesium atom. In the International System of Units, one second, by definition, is the amount of time needed for a cesium-133 atom to complete 9,192,631,770 oscillations.
Atomic clocks do not rely on nuclear decay. This is a common misconception based on terms such as "atomic energy" and "atomic bomb," in which the concept does refer to atomic decay. Like any other clock, atomic clocks use a frequency of vibration to keep track of time, in this case the vibration of charged particles i n the atom.
How do power plants produce electrical energy?
The modern world runs on electricity, the flow of electrons through a material. Large copper wires carry electrons from power plants to distant factories, homes, and businesses to provide energy that powers light bulbs, giant printing presses, and everything in between. How do power plants produce an electric current?
Power plants add energy to electrons by taking advantage of the relationship between electricity and magnetism. When an electrical conductor, such as a coil of copper wire, moves inside a magnetic field, electrons move, generating an electric current. This basic principle applies to plants that burn fossil fuels, such as coal or natural gas, to nuclear power plants, to hydroelectric power plants, and to wind turbines.
Inside the generating plant of a fossil (or renewable) fuel burning plant or a nuclear plant, potential energy, stored in chemical compounds or in the atom’s nucleus, is converted to mechanical energy—moving gases or liquids. The moving fluid turns the blades of a turbine, concentrating this mechanical energy into a spinning shaft. The shaft is attached to giant coils of copper wire that spin inside a powerful magnetic field. As electrons are forced to flow in the coils, current is transmitted and distributed throughout the power grid.
Although an electric current travels very rapidly from a power plant throughout the grid, the electrons themselves do not move rapidly. As an electron gains energy, it "bumps" another electron in the wire and passes some of its kinetic energy to that electron which in turn passes it farther down the line.
"We have also arranged things so that almost no one understands science and technology. This is a prescription for disaster. We might get away with it for a while, but sooner or later this combustible mixture of ignorance and power is going to blow up in our faces." -Carl Sagan (1934-1996)
How do home computer printers work?
The demand for inexpensive printing technology grew along with the development of inexpensive computers that could be used in businesses and homes. Although many records and processes can be handled on the computer monitor, there is still a need for paper records. They can be mailed, read without a computer, posted on a bulletin board, and some people just prefer to hold a document. How do home printers work?
There are two main types of home printers, which use completely different technologies: inkjet printers and laser printers. Generally inkjet printers are less expensive to buy and more expensive to operate than laser printers. Inkjets are used more for home color printing and are more suitable for nonpaper media, such as transfers for putting images on T-shirts. Laser printers are faster and generally have a better image quality.
In an inkjet printer, ink is squirted from a nozzle as it passes over the paper. A roller moves the paper from top to bottom while the print head that holds the ink nozzles moves back and forth, shooting ink. Each print head has several hundred nozzles that are about the diameter of a human hair. They deliver tiny dots of ink to the paper. One milliliter of ink is enough to make about 100 million dots. If you look at a page printed on an inkjet printer through a magnifying class or microscope, you can see the pattern of dots.
Inkjet printers use built-in computers to control the timing and the order in which ink is fired from the nozzles on the printing head. There are two methods for firing dots from a nozzle. Some printer manufacturers use tiny heating elements to heat the ink and create a bubble. When the bubble bursts, ink hits the paper and more ink is drawn into the nozzle. There are a couple of limitations to this technology: the ink must be heat resistant and the print head must cool between bubbles, slowing the process. The second method of ink delivery uses a piezoelectric crystal, a crystal that flexes in an electric current. Each time a current is applied to a crystal behind the nozzle, the flexing crystal creates pressure that shoots a droplet of ink. This peizo process is faster and does not require heat-stable ink, but the print heads tend to be more expensive than thermal print heads.
Laser printers use a rotating metal drum that is covered by a negative static electrical charge. When light strikes the drum, atoms absorb energy and the electrons are able to move. As the drum rotates, it is charged by an electrically charged wire. A computer in the printer then creates an image by shining a laser on parts of the drum, allowing the electrons to move away.
The drum is then exposed to toner, a fine powder containing plastic particles and carbon or coloring agents. The powder is given a negative charge, so it sticks to the parts of the drum that have been exposed to the laser but is repelled by the sections that still have a negative charge. The toner is then transferred to a sheet of paper. Heat and pressure melt the toner and press it into the paper.
How can irradiation preserve perishable foods?
You may sometimes see food, particularly produce and meats, with a label stating that it has been irradiated. Exposing foods to radiation extends their shelf lives and kills insects that may inhabit produce. How does the irradiation of food act as a preservative?
Irradiation exposes the food to electromagnetic radiation, in the form of gamma rays or x-rays. This radiation is similar to visible light but it has a much shorter wavelength and carries much more energy. Gamma rays are naturally produced by the nuclei of cobalt-60 atoms. The cobalt sample is stored in water, which absorbs the radiation. To treat food products, the food is placed in a chamber with thick concrete walls to absorb stray gamma rays and the radioactive cobalt is removed from the water.
Uncommon sense
The term "radiation" has become so associated with the toxic effects of exposure that many people are concerned about exposure to irradiated foods. However, the food does not come in contact with the source of radiation, so the consumer is never exposed to any radiation from treated foods. The process is similar to the scanning of checked luggage at an airport using x-rays.
X-rays for food irradiation are produced by machines that are similar to those used for medical x-rays, but more powerful. A high-energy electron beam strikes a gold plate, producing the x-rays.
Irradiation extends the shelf life of foods by killing microorganisms on and in the product. As gamma rays pass through living cells, their energy is absorbed by molecules in the cells. Because DNA molecules are so large, they are particularly susceptible to damage by gamma rays and x-rays. When this occurs, the cells are no longer able to reproduce and the organism dies.
During irradiation, food is exposed to radiation that is several million times as strong as that of an x-ray.
Irradiation is commonly used to treat meat, especially ground meats, in order to kill bacteria and parasites. Irradiation has very little effect on viruses, however. It is also used to destroy bacteria, fungi, and insects on fruits and vegetables, which slows spoiling. Potatoes treated by irradiation do not sprout during storage because the living tissue in the growth buds of tubers is also killed by the gamma rays.
How does biometric identification work?
As security concerns become more and more important to many governments and businesses, biometric identification methods have been proposed as a way to confirm identity. Many countries now require biometric identifiers on passports or, in some cases, driver’s licenses. What are biometric identifiers and how do they work?
The word biometric literally means "life measure." Biometric identifiers are measurable physical characteristics of a person that can be checked automatically. In the simplest form, information about height, weight, and eye color on a driver’s license is a biometric indicator. In general, however, these are not adequate for identification because they are characteristics that can change over time, or they can be altered or masked. Generally, for security applications, the term biometric indicator is used for characteristics that do not change and cannot be easily disguised and that are unique to a person.
While automated security checks were once found only in spy movies, advances in computer and camera technologies have made them increasingly common in real life. The most common features used for identification are fingerprints and handprints, facial features, and eye scans. Each method has different advantages and disadvantages.
Facial recognition is one of the most flexible techniques because it can be used without the subject even being aware of it. This is also a source of concern about the ethics and legality of the technique. Facial recognition systems analyze photographs taken with an ordinary digital camera. A number of specific measures are taken, including distances between specific points on the face, distance between the eyes, and width of the nose. These measures are combined to a unique code. The photograph does not need to be taken from a particular angle, so cameras can acquire photographs of large numbers of people in a crowd or an airport line and compare them to a database. Ethical concerns include the collection of data on large parts of the population without their knowledge and the ability to secretly track movements.
Fingerprints were one of the first biometric measures in common use, having been used by police agencies for more than a century. Fingerprints are unique identifiers— even identical twins have different patterns. Fingerprint identification involves comparing the patterns of ridges on the fingertips with a database. Scanning and comparison are so simple and reliable that they have even been installed in business computer systems and personal digital assistants. For some applications, handprints that scan the entire hand are more useful.
The pattern of blood vessels in the retina is also unique and appears to be unchanging through life. Unlike fingerprints, retinal scans cannot be obscured by dirt or scarring, so they have become a standard method of identification for many military installations. The main drawback of retinal scans as a routine identifier is the fact that the subject must undergo a 15-second scan, keeping the eye in position.
Iris scans look at the patterns of rings, furrows, and light and dark spots in the iris, which surrounds the pupil of the eye. Like a retina scan, the iris scan provides a unique identifier that is not subject to wear or being obscured. Currently, iris scans are slightly easier to obtain than retina scans and they can be acquired through corrective lenses. Commercial systems already exist that use a computer matching program to compare iris scans to a database for positive identification. Some countries have used them as part of their immigration programs for several years without a false match. You can even buy an iris recognition system that you can attach to your computer to lock out unauthorized users for about $150.
