Maximum power transfer theoremIn electrical engineering, the maximum power transfer theorem states that, to obtain maximum external power from a power source with internal resistance, the resistance of the load must equal the resistance of the source as viewed from its output terminals. Moritz von Jacobi published the maximum power (transfer) theorem around 1840; it is also referred to as "Jacobi's law". The theorem results in maximum power transfer from the power source to the load, and not maximum efficiency of useful power out of total power consumed.
Cordless telephoneA cordless telephone or portable telephone has a portable telephone handset that connects by radio to a base station connected to the public telephone network. The operational range is limited, usually to the same building or within some short distance from the base station. A cordless telephone differs functionally from a mobile telephone in its limited range and by depending the base station on the subscriber premises.
RadiometerA radiometer or roentgenometer is a device for measuring the radiant flux (power) of electromagnetic radiation. Generally, a radiometer is an infrared radiation detector or an ultraviolet detector. Microwave radiometers operate in the microwave wavelengths. While the term radiometer can refer to any device that measures electromagnetic radiation (e.g. light), the term is often used to refer specifically to a Crookes radiometer ("light-mill"), a device invented in 1873 in which a rotor (having vanes which are dark on one side, and light on the other) in a partial vacuum spins when exposed to light.
Super low frequencySuper low frequency (SLF) is the ITU designation for electromagnetic waves (radio waves) in the frequency range between 30 hertz and 300 hertz. They have corresponding wavelengths of 10,000 to 1,000 kilometers. This frequency range includes the frequencies of AC power grids (50 hertz and 60 hertz). Another conflicting designation which includes this frequency range is Extremely Low Frequency (ELF), which in some contexts refers to all frequencies up to 300 hertz.
Radio waveRadio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz (GHz) and below. At 300 GHz, the corresponding wavelength is 1mm, which is shorter than the diameter of a grain of rice. At 30 Hz the corresponding wavelength is ~, which is longer than the radius of the Earth. Wavelength of a radio wave is inversely proportional to its frequency, because its velocity is constant.
