What's involved in making TV programs?

Insights

Behind-the-scenes at Newton's Apple, a team of performers, producers, directors, engineers, and editors work feverishly to produce a 30-minute, award-winning program. But how do the scenes that are shot in the studio and on location get converted from live action to videotaped entertainment?

To understand how television works, you need to know about light, sound, and electromagnetic waves. Simply put, a television camera turns the light and sound of live action into pulses of electricity that are transmitted from the television station in waves, and are then received by your television. Your TV reverses the process by turning electromagnetic waves back into light and sound, allowing you to see the images.

Using Newton's Apple as an example of this process, light bounces off of David and enters the television camera. The camera changes the light into electronic video signals. Simultaneously, the microphone picks up the sound of David's voice and changes it to electronic audio signals. To produce the electronic color signals, the camera separates David's image into the three primary colors of light: red, blue, and green.

When the program is broadcast, the electronic signals are sent to the station's transmitter. Here, the signals are converted to electromagnetic waves. This transmitter first produces a powerful carrier wave onto which both the video and audio signals are placed. The carrier wave is at a specific frequency, which you tune in on your TV dial. These waves are emitted by the station's antenna and are received by the antenna at your home.

When you turn to your PBS channel, you select the frequency on which the Newton's Apple transmitter is broadcasting. The television receiver sorts out that frequency from among the others, allowing only the signals specific to that channel to come through. The receiver also separates the audio from the video signal, sending the audio to the speaker and the video to the picture tube. The video signal is then separated into signals for each primary color. Each color signal has its own electron gun that sweeps across the inside of the picture tube and excites the more than 300,000 phosphor dots coated on the television tube. The picture emerges as the guns quickly scan the entire screen to create an image of David in lifelike color.

Connections

1. Eighty-nine million homes in the U.S. have televisions for entertainment. List all the possible uses of TV.
2. How long has television been around? Who invented it? How are television and radio technology similar?

Vocabulary

antenna conducting metal used to receive or send electromagnetic signals
channel a group or band of frequencies that carries a television transmission
electromagnetic waves that have electrical and magnetic properties (i.e., visible light, X-rays)
frequency the number of cycles or complete waves transmitted in one second
phosphor a substance that emits light when struck by electrons
transmitter a device that broadcasts electrical impulses in the form of waves

Resources

Corbett, S. (1965) What makes TV work? Boston: Little Brown.

Macaulay, D. (1988) The way things work. Boston: Houghton Mifflin.

Potter, T. (1990) How television works. Great Britain: Times Four Publishing LTD.

VanCleave, J. (1991) Physics for every kid. New York: John Wiley and Sons.

The visual dictionary of everyday things. (1991) New York: Dorling Kindersley.

Additional source of information:
Edmund Scientific
101 E. Gloucester Pike
Barrington, NJ 08007
(609) 573-6250
(science kit: Adventures in science: Color and light)

Community resources:
Television stations
Broadcast engineers
Vocational colleges

Main Activity

Turn on a color television set and the screen lights up with tiny red, blue, and green dots. Because the dots are close together and change quickly, our brain mixes these colors together to produce an incredible assortment of colors. Mix colored lights together and see what happens.

Materials

• red, blue, and green 100-watt floodlamp lightbulbs OR red, blue, and green cellophane gels (available at art supply stores) to place over white or clear bulbs
• 3 clamp-on photo floodlamp or spotlight receptacles OR 3 standard flashlights
• standard projection screen OR a large sheet of white paper or fabric taped to a wall

1. Set up the different-colored spotlights so that they are all aimed at a central spot on your screen. (Try clamping them on the backs of three chairs or a table top, positioned about six feet back from the screen.)
2. Make the room as dark as possible and turn on the spotlights, adjusting them so that the combination of their light produces a whitish color on the screen.
3. Turn off the red spotlight. What color is evident now? Repeat by turning off the blue and green spots while leaving the others on. How many different colors can you get from only three colored lights?
4. Stand about halfway between the screen and the spots and wave your hands back and forth. What happens to the colors on the screen?

Note: The same procedure can be done with students holding flashlights and aiming the beams at a central point on the screen. However, it may be harder to create the colored shadows using this method.

Questions

1. Why do the colors on the projection screen change when you move your body in front of them? How might this relate to electron guns in a television set turning on and off?

2. Television isn't the only medium that uses color-blending to create full-color images. How does this same principle relate to the printing of color pictures in newspapers, or the processing of satellite images of the earth?

Invite a television-repair person to visit your class and bring along a broken television set. Talk about and label the various parts of the television set and learn more about how your own television works.

Television flashes a series of images so fast that your eye sees them as one moving image. Make a flickerbook to help understand this idea. Take a small pad of paper stapled together at one end. Draw a series of simple images, such as a seed growing. Working from the last page to the first, draw the images with incremental differences. When done, flip through your book from the last page to the first.

Videotape your own version of Newton's Apple. Divide the class into "production teams" and have each team select a science question to explore. Individuals can be assigned the specific responsibilities that go into making a television show: researcher, producer, director, performer, and videotape technician. Combine all the segments into one program and invite another class in for the official viewing.

Take a magnifying glass and look closely at a show playing on your television set. Do you see the phosphor dots? Where else might you find the concept of tiny dots forming images? Which of your examples uses the colors of light and which uses the colors of pigment?

Newton's Apple is a production of KTCA Twin Cities Public Television.
Made possible by a grant from 3M.
Educational materials developed with the National Science Teachers Association.