1. Black and white TV
Black-and-white TV is a kind of TV that can only display black and white. In the early days of TV development, including the recording of TV programs, the reception and display of TV sets, all can only reflect black and white. Using electronic technology and equipment to transmit moving images and audio signals, that is, TV receivers, is also an important tool for broadcasting and video communication. Television uses electricity to transmit moving visual images instantly. Similar to movies, TV uses the visual residual effect of human eyes to gradually change the still image frame by frame to form a visually moving image.
2. Radio
The radio is the receiver of radio broadcasting. The weak signal of high-frequency modulation input from the receiving antenna is amplified, converted into audio signal after frequency conversion and detection. According to different needs, the radio can be combined with different components and circuit modes. Early radios used electron tubes, but now transistors and integrated circuits are widely used. Regenerative radios with simple circuits use only one transistor, while superheterodyne AM FM radios with complex circuits often use multiple integrated circuits.
3. electric light
Electric light is a device that converts electric energy into light energy to provide lighting, which appeared in the second industrial revolution. Its working principle is that when the current passes through the filament (tungsten filament, melting point above 3000℃), heat is generated, and the spiral filament continuously accumulates heat, so that the filament temperature reaches above 2000℃. When the filament is incandescent, it shines like hot iron. The higher the temperature of the filament, the brighter the light it emits.
4. flashlight
Flashlight, referred to as flashlight, is a hand-held electronic lighting tool. A typical flashlight has a battery-powered light bulb and a focusing lens, and a handle-type housing for holding. Although it is a fairly simple design, it was not invented until the end of 19, because it must combine the invention of battery and light bulb. In the early days, the battery was called "flashlight" in English because of its insufficient storage capacity, which means short-lived lamp.