cathode-ray tube, or filmed TV program {kinescope}.
In an old process {orthicon}|, light hits a surface to emit electrons, electrons focus on a target, and target emits electrons that carry image signal from camera to television set.
Machines {radar}| can use a magnetron to emit radio waves and then receive wave reflections, to determine speed and position by Doppler effect.
Antennas {radio frequency identification tags}| (RFID) attached to circuits can activate by magnetism or radio waves. RFID are in tollbooth signalers and security systems, to identify. In low-frequency systems activated by magnetism, circuit resistance becomes high or low by turning transistor on and off, generating a magnetic field in tag {load modulation}. In high-frequency systems activated by radio waves, turning transistor on and off causes tag dipole antenna to reflect or absorb radio waves {backscatter modulation}.
Receivers {radio, machine}| can convert electromagnetic radio waves with frequency range near 10^-6 Hz to electric current. Radio waves carry sound information in frequency modulation (FM) or amplitude modulation (AM). An adjustable LC circuit {tuner} selects radio-station frequency. A circuit {filter, electronic} removes radio-station carrier frequency and leaves sound vibrations that ride on carrier wave {demodulation}. A tube or transistor amplifier increases amplitude. Speakers change electric current into sound, by vibrating an inductance coil attached to a paper cone.
Devices {television}| can display pictures and sound.
parts
A glass vacuum cathode-ray tube has an electron emitter {electron gun} at pointed end and a flat front surface coated by chemicals {phosphor} that glow after being struck by electrons.
scanning
Electromagnets outside tube direct electron paths horizontally and vertically. A single electron beam moves row by row across screen and covers whole screen once every 1/30th second.
brightness
A positive electrode controls electron stream from electron gun. Beam can be more or less to make picture lighter or darker {brightness control}. Another positive electrode {contrast control} controls difference between light and dark areas.
controls
Side electromagnets can shift picture horizontally {horizontal control} or vertically {vertical control}.
synchronization
TV signals contain synchronizing signals, so TV cameras and home TVs sweep scene at same rate. TV sound is broadcast separately from picture on FM radio.
frequency
TV has higher frequencies than radio: very high frequency (VHF) or ultra high frequency (UHF).
Elograph (George Samuel Hurst) had electrically sensing coordinates on a computer screen {touch screen}| [1971]. Screens later had a transparent surface [1974]. Today, screens use five-wire resistive [1977], surface acoustic wave, or capacitive technology.
To make images {vidicon}|, an electron beam can scan an image to find point intensities.
7-Machine-Kinds-Electronic-Light
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Date Modified: 2022.0225