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#Scince behind cathode ray tube television tv

#Scince behind cathode ray tube television tv

Your cable provider could simply modulate the different cable-TV programs onto all of the normal frequencies and transmit that to your house via the cable then, the tuner in your TV would accept the signal and you would not need a cable box. The cable in cable TV contains a large number of channels that are transmitted on the cable.

The VCR has a circuit inside that takes the video and sound signals off the tape and turns them into a signal that, to the TV, looks just like the broadcast signal for channel 3 or 4. The video tape contains a composite video signal and a separate sound signal. Almost all VCRs have a switch on the back that allows you to select channel 3 or 4. VCRs are essentially their own little TV stations. In the next section, you'll learn about the color TV signal. All other colors on a TV screen are combinations of red, green and blue. To create a black dot, all three beams are turned off as they scan past the dot. To create a white dot, red, green and blue beams are fired simultaneously - the three colors mix together to create white. When a color TV needs to create a red dot, it fires the red beam at the red phosphor. This mask is perforated with very small holes that are aligned with the phosphor dots (or stripes) on the screen.

On the inside of the tube, very close to the phosphor coating, there is a thin metal screen called a shadow mask.

If you turn on your TV or computer monitor and look closely at the screen with a magnifying glass, you will be able to see the dots or stripes. Instead, the screen is coated with red, green and blue phosphors arranged in dots or stripes.

The screen is not coated with a single sheet of phosphor as in a black-and-white TV.

They are named the red, green and blue beams.

There are three electron beams that move simultaneously across the screen.

The term horizontal retrace is used to refer to the beam moving back to the left at the end of each line, while the term vertical retrace refers to its movement from bottom to top. When the beam is "painting," it is on, and when it is flying back, it is off so that it does not leave a trail on the screen.

When the beam reaches the right side of the bottom line, it has to move back to the upper left corner of the screen, as represented by the green line in the figure. In this figure, the blue lines represent lines that the electron beam is "painting" on the screen from left to right, while the red dashed lines represent the beam flying back to the left. It then quickly flies back to the left side, moves down slightly and paints another horizontal line, and so on down the screen. The beam paints one line across the screen from left to right. To "paint" the entire screen, electronic circuits inside the TV use the magnetic coils to move the electron beam in a " raster scan" pattern across and down the screen.

In a black-and-white TV, the screen is coated with white phosphor and the electron beam "paints" an image onto the screen by moving the electron beam across the phosphor a line at a time.