Table of Contents
Teaching Tip: How the Light Bulb & the Telephone Work
What if the only way you could communicate with someone living in another city was by mailing them a letter, one that might take weeks to get delivered? (Even with our modern technology, it still takes at least two weeks for mail to get to some countries.) The telephone is certainly one of the greatest inventions in the history of communication!
The inventor of the telephone, Alexander Graham Bell, was born in Scotland in 1847, the same year as Thomas Edison. He went to university in Edinburgh and London, then immigrated to Canada in 1870 and to the U.S. a year later. There he used visible speech (a type of phonetic notation that shows the position of the throat, mouth, and tongue to make different sounds) to teach deaf-mute people how speak.
When he was a young man, Bell became interested in transmitting speech, the way a telegraph transmitted messages. In 1874 he developed the idea for the telephone and successfully created and patented one two years later. (Just two hours after he applied for his patent, Elisha Gray filed his intention to apply for a patent for a very similar device.) His first transmitted sentence was to his assistant: 'Watson, come here; I want to see you.' Bell demonstrated his telephone at the Philadelphia Centennial Expo and in 1877 organized the Bell Telephone Company.
So how does this amazing invention work? How can you talk to someone miles away and hear them as though they were in the same room with you? It's actually a fairly simple process. At its most basic, a telephone consists of a switch, a receiver, and a microphone. The switch connects your phone to the telephone network; the receiver changes electrical signals into sound waves so you can hear the other person, and the microphone changes the sound waves you make into electrical impulses to send to the other end of the line.
The microphone contains carbon granules and a thin metal diaphragm. When you speak, the sound waves (vibrations in the air) hit the diaphragm and cause it to move, compressing the carbon granules behind it. A louder sound will compress the granules more than a soft sound. When the carbon is compressed, an electrical current can flow through it more easily. A battery (either in your handset or at the telephone company) sends an electric current through your phone; when you speak, the compression of the carbon varies the intensity of the current.
Experiment with electricity and sound transmission with this kit for kids!
This process is reversed at the other end of the line by the receiver. The electrical current flows through an electromagnet in the receiver, producing a magnetic field. This magnetic field attracts the thin metal diaphragm in the receiver, causing it to move in and out. As it does so, it pushes and pulls the air, creating sound waves. These waves reach your ear with the same intensity as they were spoken, allowing you to hear what the other person said.
The process hinges on the ability to have a variable electrical current. Unlike the telephone, a telegraph operates on a constant electric current - the messages are transmitted not by changing the current, but by repeatedly turning it on and off in a distinct pattern. Because the human voice doesn't start and stop sound waves in the same way as tapping Morse code does, the current must be able to adjust for variation in volume and frequency. The carbon microphone allows for this variation, giving us the ability to transmit speech electrically.
Bell probably couldn't have imagined the kind of communication we have today. Not only do we have long-distance telephone networks all over the world, we also have cellular phones that use radio frequencies to allow us to talk wirelessly wherever we are. Communication was changed forever by the telephone and continues to develop rapidly today.
Perhaps one of the most important inventions of all time is the electric light bulb. We could get by with candles or lanterns in our homes, but imagine trying to shop at the mall, work in a large office complex, or travel at night by car or plane without electric lighting!
Thomas Alva Edison, one of the developers of the modern light bulb, is also one of the most famous as well as prolific inventors in history. He patented over 1000 inventions in his lifetime. Edison was born in Ohio in 1847. As a child, he received less than a year of formal schooling, but was educated at home. His parents allowed him to set up a laboratory in their basement and his mother gave him books about chemistry and electronics. Edison credits his mother as being 'the making' of him.
When he was 12, Edison got a job selling newspapers on a train that made day trips between his hometown of Port Huron, Michigan and Detroit. He took his laboratory along in the baggage car so that he would be able to experiment during layovers. This worked until one day some of his chemicals spilled and started a fire! Also while working on the train, Edison saved the child of one of the station masters, and as a reward was taught how to use a telegraph machine. He became a telegraph operator and began making improvements to the telegraph's functionality. He later invented a way for multiple telegraph messages to be transmitted simultaneously (rather than one at a time).
As a young man, Edison moved to New York City and eventually established a laboratory. In 1877 he invented the phonograph, which used a record made of tinfoil to play back sound. In 1879 he created a successful incandescent light bulb. This was his hardest project - from 1877 to 1880, Edison and his assistants tried around 3000 experiments to perfect their light bulb design. By the end of 1880, Edison had produced a bulb that lasted 1500 hours. (This has a moral: don't worry if some of your own science experiments aren't a success the first time you try them!)
Experiment with electricity with our student-friendly kit!
Edison was not the first person to make a working light bulb: In the 1860s another English scientist, Sir Joseph Wilson Swan, began experimenting. He made a light bulb that used carbonized paper for a filament. But Swan lacked a strong enough vacuum inside the bulb; a design problem that he corrected at almost the same time Edison did. After a legal battle between the two inventors, Edison and Swan teamed up and created the company Ediswan to market their invention.
How exactly do light bulbs work? For being such an important part of our lives, they have a fairly simple design. The base contains two metal contacts, which connect to an electrical circuit. These contacts are attached to two wires, which are in turn attached to the filament in the middle of the bulb (the filament is usually supported by a glass mount). A power supply sends an electric current from one contact to the other, traveling up through the wires and the filament. As the current passes through the filament, it "excites'' the atoms that make up the filament material, causing them to give off energy in the form of heat and light. Edison tried thousands of different materials for his filaments, but most of them produced light for only a short time. He finally tried a carbonized cotton thread, which burned for many hours. Eventually, light bulbs were made using the metal tungsten for the filament. Tungsten works well because it has an unusually high melting point. This is important because metal must be heated to extreme temperatures to give off enough light.
The danger of running electrical current through the filament is that the resulting high temperatures may cause the filament to combust, or catch on fire. This will only happen if oxygen is present, so Edison sucked all the air out of his glass bulbs to create a vacuum. This method worked fine to prevent combustion, but it allowed filament atoms to evaporate, shortening the life of the bulb. In modern bulbs, the glass is filled with an inert gas, such as argon. This prevents combustion, and also helps prevent tungsten atoms from evaporating.
For over a century we have read and worked by the light of Edison's incandescent bulb. Other light sources, such as fluorescent bulbs and LED, have gained popularity in recent years because of their efficiency. The incandescent bulb releases most of its energy in the form of heat, not light, thus wasting electricity. Fluorescent and LED, however, are much cooler, and release most of their energy as visible light. These light sources have replaced the incandescent bulb for many functions.
Although almost all of Edison's discoveries were technological rather than strictly scientific, his invention credits include an alkaline storage battery, microphone, mimeograph (a copy machine), and a kinetoscope for viewing moving pictures. He also created the first 'talkie,' a movie that had sound, using his kinetoscope and phonograph. He continued to improve not only the incandescent light bulb, but some of his other inventions like the phonograph as well.
Make a light bulb
Thomas Edison tried thousands of experiments when he was inventing the incandescent light bulb. You can experiment too, and find out how a light bulb really works, by making your own! You will need a glass canning jar with a lid, three feet of insulated copper wire, a 6-volt battery, and thin iron wire (unraveled picture hanging wire works great).
Cut the copper wire into two equal sections. Strip at least one inch of insulation off the ends of each length of wire. Next, punch two holes in the jar lid (you can use a nail for this). Thread a wire through each hole in the lid. Make a hook at the end of each wire (the end that will be inside the jar when you put the lid on). Twist two or three strands of iron wire together, then twist the ends around the hooks in the copper wire. The iron wire will act as your filament.
Place the lid (with the filament) in the jar and carefully connect the free ends of the copper wire to the 6-volt battery. Once both ends are connected, the current should start flowing, causing the filament to heat up and give off a bright orange glow. Your homemade light bulb is working! (Note: once your filament is burned out, don't touch it right away - it will be very hot.)
For full instructions on making and experimenting with propellers, read the rest of this science project!
On December 17, 1903, Orville Wright flew the first powered, heavier-than-air airplane, propelling himself and his older brother Wilbur into world history. It took the brothers years of preparation to get to that cold and windy day in Kitty Hawk, North Carolina.
Wilbur (born in 1867) and Orville (born in 1871) grew up in Dayton, Ohio, the son of a United Brethren minister. Both of their parents had college educations, and they fostered intellectual curiosity and experimentation in their children. Bishop Wright sparked his young sons' interest in flight early on by bringing them a special toy - a flying top. This toy was essentially a rubber-band powered helicopter. The boys flew it until it fell apart, and then Wilbur built his own. As they grew older, the boys spent much of their time designing, building, and selling kites.
As young adults, Wilbur and Orville capitalized on the booming popularity of bicycles by starting their own bicycle sale and repair shop. Eventually they started building their own bicycles, which was excellent training for their next enterprise: building a flying machine.
Wilbur and Orville read everything about flight that they could get their hands on in Dayton. To get more information, Wilbur wrote the Smithsonian asking for up-to-date materials on the study of flight. With the Smithsonian's help they studied Sir George Cayley's work with the four forces of flight (lift, gravity, thrust, and drag), others' experiments with gliders, and the attempts at flight made by the Smithsonian's secretary, Samuel Langley. All the work these men had done, even when they failed, proved indispensable to the Wrights' efforts. After carefully studying, Wilbur and Orville began their own scientific analysis of what was needed for flight, and began designing their own gliders. They didn't just want to put an airplane in the sky; they wanted controlled flight, and for this they needed to master the three axes of motion: pitch, roll, and yaw.
Pitch is the up and down motion of the airplane's nose (climbing or diving). Roll is the airplane rolling from side to side, causing its wings to tilt up or down. This is especially necessary for turns. When an airplane turns left, it doesn't just remain level; the left wing will dip down and the right wing will be raised up. The last of the three axes is yaw, which is the airplane's right and left movement.
Orville and Wilbur realized that birds control pitch, roll, and yaw by adjusting the shape of their wings. The brothers tried to mimic this by developing what they called 'wing warping,' a system of wires and pulleys that manipulated the glider wings to allow banking turns to the left and right. At first the wing warping was controlled with the pilot's feet, but eventually they designed a hip cradle, which was easier to use. The pilot shifted his hips right, the wires pulled the left wingtips up, and the glider banked to the right. Wing warping took care of roll; their front elevator controlled pitch, and eventually the brothers controlled yaw by connecting wires from a rudder to the hip cradle.
In the autumn of 1900, the Wrights packed up a glider and set up camp at a deserted and windy beach outside of Kitty Hawk, NC. For three weeks they flew their glider as a kite, before trying to pilot it. Though they didn't achieve as much lift as they expected based on the lift tables established by aviation researchers, they were very happy with the results of their first Kitty Hawk visit. Their best flight lasted 15 seconds and covered 300 feet.
1901 saw the brothers back at Kitty Hawk, this time with an upgraded glider. The flight tests did not go as they had hoped. The new glider proved much more difficult to control, and they simply could not get the amount of lift they were trying for. They went home to Dayton discouraged and ready to give up. Men will certainly fly, they thought, but not in our lifetime. In the end, they decided to persevere. The lift tables widely accepted by the other pioneers in flight must be wrong. The Wrights decided to test the tables; they built their own wind tunnel in the back of their bicycle shop, and observed its effects on 200 different types of miniature wings.
With the information they gathered from their wind tunnel experiments, the brothers built yet another glider for testing in 1902. This was the first flying machine that had controls for all three axes of motion. It flew smoothly, was controlled easily, and glided more than 600 feet several times. They had a maneuverable aircraft; now they needed power.
True to form, the Wrights decided to build their own engine for their plane (named 'The Flyer'). The finished product put out 12 horsepower and weighed 180 lb (the entire plane weighed 605 lbs). Then came the real challenge: designing propellers. One of their greatest contributions to aviation turned out to be their pioneer research on propellers. Their final product had 70% efficiency, which is nearly as good as modern propel ers! Back at Kitty Hawk in the fall of 1903, they began assembling The Flyer. Bad weather and damage to the plane delayed flying for several months, but finally in mid-December they were ready. Because wheels would make the plane too heavy, the Wrights constructed a wooden track for the plane to move on when taking off. On December 17th, Orville climbed onto The Flyer and started the engine. It moved down the track and lifted into the air. That first flight last only 12 seconds and covered 120 feet, but it was still the first-ever controlled, heavier-than-air flight. The brothers flew the plane four times that day, and the fourth time Wilbur flew for 59 seconds, covering 852 feet.
After this breakthrough the Wrights continued to improve their plane. Now that they weren't dependent on the winds for power, they left the beaches of Kitty Hawk and moved their work to an Ohio field. By 1905, Wilbur was flying laps around the field: 24.5 miles in 39 minutes. In spite of this success, the brothers couldn't find a buyer for their invention. They decided to stop flying until they could get a sales contract. Three years later, in 1908, they received offers from the French and from the U.S. Army. Wilbur packed up a plane and went to France, where he became something of a celebrity by flying figure eights and taking up passengers (this later model had two seats). Orville demonstrated his plane for the U.S. Government and impressed them with his altitude of 300 feet, hour-long flights and average speed of 42.58 miles. They paid him $30,000 for the plane.
The age of aviation had 'taken off,' so to speak. Just 44 years after that first powered flight, airplanes began flying faster than the speed of sound; in another 14 years men were flying in space; another eight years after that they were walking on the moon. The Wright brothers' passion and perseverance laid the foundation for this astonishing and speedy technological advance.
Major coil: In a normal 60-watt bulb, the tungsten filament is made of a piece of metal six-and-a-half feet long, but only one-hundredth of an inch thick. This is "double coiled" (coiled once, and then that coil is wound up into another coil) so tightly that the filament ends up being less than an inch long!
Edison's genius: You may have heard the famous saying, 'Genius is one percent inspiration and ninety-nine percent perspiration.' Thomas Edison is the inventor who said it. His genius required years of tedious work and thousands of experiments to create the incandescent light bulb. Next time you turn on a lamp, think of Edison's inspiration and hard work!
Hello, Operator? Today when you dial your phone a computer connects you automatically with the person you are calling. In the early days of the telephone, however, your call went through a manual switchboard. An operator sat in front of a board with jacks for each house connected to the network. When someone picked up their telephone, the light above their jack on the switchboard would turn on. The operator would ask them who they were calling and then connect them with the appropriate person.
This page has illustrations and animations explaining how your telephone works.
Go to this site to view the Library of Congress collection of the Alexander Graham Bell Family Papers.
Click here to see a picture of the Wright brothers' very first flight.
Want to try your hand at some fancy paper airplanes? Check out this site!
Even more about Edison! This site has lots of info about Edison - his inventions, his patents, his home...it even has some of his home movies, made on his kinetoscope!
NOTE: Home Science Tools does not necessarily agree with or endorse all opinions and information expressed on the sites linked in this newsletter. Please use at your discretion.