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The control grid is an electrode used in amplifying thermionic valves (vacuum tubes) such as the triode, tetrode and pentode, used to control the flow of electrons from the cathode to the anode (plate) electrode. The control grid usually consists of a cylindrical screen or helix of fine wire surrounding the cathode, and is surrounded in turn by ...
Thermosyphon circulation in a simple solar water heater (not a working model; there is no water supply to replenish the tank when the tap is used). A thermosiphon (or thermosyphon) is a device that employs a method of passive heat exchange based on natural convection, which circulates a fluid without the necessity of a mechanical pump.
English: Active indirect water heater. 1: Municipal water feed 2: Fluid from water storage tank to external (passive) heat source; passive heat source can be the ground (soil or groundwater), sun or air; eg via heat pump, or thermodynamic solar panel 3: Fluid from heat pump, or thermodynamic solar panel to water storage tank 4: Pump, actuator, controller and other parts 5: Water heater 6 ...
The terms anode and cathode are not defined by the voltage polarity of electrodes, but are usually defined by the direction of current through the electrode. An anode usually is the electrode of a device through which conventional current (positive charge) flows into the device from an external circuit, while a cathode usually is the electrode through which conventional current flows out of ...
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Electrons can flow in only one direction through the device: from the cathode to the anode (hence the name "valve", like a device permitting one-way flow of water). Adding one or more control grids within the tube, creating the triode, tetrode, etc., allows the current between the cathode and anode to be controlled by the voltage on the grids ...
In fact, by about 1930 there was agreement that, due to the wave-like nature of electrons, some proportion r av of the outgoing electrons would be reflected as they reached the emitter surface, so the emission current density would be reduced, and λ R would have the value 1 − r av. Thus, one sometimes sees the thermionic emission equation ...
A thermostat exerts control by switching heating or cooling devices on or off, or by regulating the flow of a heat transfer fluid as needed, to maintain the correct temperature. A thermostat can often be the main control unit for a heating or cooling system, in applications ranging from ambient air control to automotive coolant control.