Have you ever wondered how a TV works?

It is on everybody's home, and many will waste countless hours watching. You grew up with it, but do you know what's inside a TV? Why is it even possible to make such a gadget? Who invented it? Although you won't be able to build one from scratch after you read this, you can certainly understand better how TV was invented and what's inside. To understand precisely how it works, though, you would need to know Electrical Engineering, Physics and Mathematics quite well. Nevertheless, we can find out who invented each component of the TV, learning the Physics principles in which TV relies on. Many physicists, engineers and inventors made seemingly unrelated discoveries before a TV could be conceived. What's inside a TV? Well, we have an antenna, a glass tube with a screen on it, a speaker and electric circuits. We also need a broadcaster with a TV camera and another antenna. You probably understand that some kind of electric message is carried through air. This message we call a signal. The broadcaster's antenna sends or transmits the signal that contains the image and sound on a TV channel. The TV's antenna then picks up or receives this message. The circuits inside then transform this signal in such a way that it can be displayed on the screen. Easy, right? Wrong, it took centuries for people to realize it was possible. First, let's understand what a TV signal is. This signal is a color of light that our eyes are not able to see. Indeed, our eyes cannot detect all colors of light.

Isaac Newton (1704) and Christiaan Huygens (1690) began to understand what light was. Newton thought light of different colors had different energies, while to Huygens light was some kind of wave, like the ones you make in a calm pond when you throw in a rock. Later, in the 19th century, hundreds of physicists worked to understand electricity better. After many experiments someone finally put together all this knowledge into a set of rules that could be used to control electricity and magnets! James Clerk Maxwell discovered in 1873 that different colors of light could be produced by means of electricity.

This knowledge was used to transmit messages, and the radio was soon created. Heinrich Hertz used electricity in antennas to produce electric signals (radio waves or `invisible light') in 1888. Using this discovery, Guglielmo Marconi started to send wireless messages in 1895 trough a telegraph, and Reginald Fessenden first transmitted voices in 1900. Voices were already transmitted through wires by Alexander Bell, the inventor of the telephone in 1875.

How about a TV screen? A TV screen is not very different from a light bulb. It has glass around it, and the air is sucked out of the glass tube. It also has a little wire that glows, but it produces electricity instead of light. J.J. Thomson discovered the nature of the electricity inside these tubes in 1897. A beam of electricity travels very quickly from the a wire in the back of the tube onto the screen. This beam of electricity is bent electrically such that it draws an image on the screen every 60th of a second. The screen is covered with a layer of phosphor that glows when electricity is hitting it. How can a TV signal be made to bend the electricity beam inside a tube to draw an image? The electric circuits that can do this job were studied in the 19th and 20th centuries by scientists like Georg Ohm and Gustav Kirchoff. Important components of a circuit are made of carbon, copper, aluminum, mica, glass and plastic. A circuit can manipulate the flow of electricity in a wire like if it were water flowing around some system of pipes, valves and pumps. Changes in the flow of electricity serve as a code that can carry information describing sound or images. How does a camera work? It converts an image into an electric signal that can be transmitted by an antenna. Maxwell's theory described the fact that electricity produced light, but also light produced electricity. A little piece of metal inside a bulb will emit electricity when hit by light, as discovered by Albert Einstein in 1905.

The TV was invented and assembled by Philo T. Farnsworth in 1927, who ingeniously put everything together. Thus, TV was possible because we could control natural electric forces. These electric forces and light itself were understood by physicists more than fifty years before Farnsworth! We can therefore distinguish two different areas of knowledge: Science and Technology. Technology is the know-how required to build new machines using our knowledge of Science, like Farnsworth did using all the knowledge about electricity and light gathered before him. Sciences like Physics not only let us understand Nature but can also be useful in our everyday lives, provided we wait long enough for an application to be devised.

Electricity: Fluid that carries a very special force. This electric force is different than gravity because it can attract or repel objects (like magnets). Batteries produce electricity.

Electric circuits: Set of cables and devices made to control the flow of electricity at will.

Isaac Newton (1642-1727): English physicist that described the relationship between forces and motion and explained gravity. He is one of the founding fathers of physics.

Christiaan Huygens (1629-1695): Dutch physicist that discovered that light propagates like a wave. He also discovered one of Saturn's moons.

James Clerk Maxwell (1831-1879): English physicist that unified the understanding of electricity and magnets under one theory. He discovered that electricity could produce light and vice-versa by putting together results of experiments in one mathematical formula.

Heinrich Hertz (1857-1894): English scientist that first successfully transmitted and received radio waves. He is said to think his invention was of `no use whatsoever', and only proved Maxwell's theories right.

Guglielmo Marconi (1874-1937): Italian that invented and commercialized the wireless telegraph and first sent a radio signal across the Atlantic.

Joseph Thomson (1856-1940): English physicist that discovered that the rays produced in a wire (called a cathode) inside a glass tube are actually the same fluid inside electric circuits. These rays were called cathode rays, so that the glass tube was called a cathode ray tube, a terminology that is still used 100 years later. To produce these rays, a battery is connected to the wire and the screen.

Georg Ohm (1789-1854): German mathematician that described the relationship between energy in a battery and the amount of electricity flowing on a circuit.

Gustav Kirchoff (1824-1887): German physicist that described the manner in which electricity flows in complex circuits. He also explained features in the colors of light coming from the sun.

Albert Einstein (1879-1955): German scientist that explained how light incident on a piece of metal will generate electricity if the piece of metal is in vacuum (i.e. vacuum means there is no air inside a tube). This is called the photoelectric effect. Einstein is also famous for his theory of gravity and space-time.

Alexander Bell (1847-1922): American inventor of the telephone.

Reginald Fessenden (1866-1932): Canadian inventor that first transmitted voice through radio waves.

Philo T. Farnsworth (1908-1971): American inventor that built the first modern TV and TV camera. Other scientists also worked on the same problem with more limited success, like Nipkow, John Baird, Zworykin, and Jenkins.

Technology: Knowledge required to use Science to build machines or tools.

To know more:
History of TV, Albert Abramson (1987).
Please stand by: a pre-history of TV, Michael Ritchie (1994).
Zworykin, pioneer of TV, Albert Abramson (1995).
Web sites:
The exciting story of the inventor of TV.
Information about the inventor of telegraph.
Biographies of famous mathematicians.