On a clear day, with just the help of your eyes you can see at most things that are fifteen miles away. Not counting the sun, the moon and the stars. How can you see with your eyes things that happen thousands of miles away, and very clearly also? Through television.
When you watch TV, you are actually seeing millions of points of light. Many miles away, a television camera is taking the picture in a studio. A transmitter broadcasts television signals, that is, copies of the images formed on the television camera. These signals are transmitted from one antenna to another until they reach the antenna of your device. They move inside it and are transformed into particles of electricity called electrons. Electrons beam out through a cannon inside the picture tube.
When starting your television, the beam of electrons leaves the cannon towards the dark TV screen. When electrons collide with the dark screen, form a luminous point.
If few electrons hit the screen, the image is black. If more electrons collide, the image is gray. When many electrons collide with the screen, the image is white.
To form a complete picture, the electron beam starts at the top end and runs in a line across the screen: line by line and one below the other. When the beam reaches the lower edge of the screen, jump back to the top to form another image. The electron beam forms many images, and these are so fast that your eyes are still seeing the last image when the new one has already arrived on the screen.