electric heater is an electrical appliance that converts electrical energy into heat. The heating element inside every electric heater is simply an electrical resistor, and works on the principle of Joule heating: an electric current flowing through a resistor converts electrical energy into heat energy.Domestic electrical underfloor heating:These systems are called radiant heating systems, regardless of whether they include a heat exchanger (also called a radiator) or are electrically powered.
When a home radiant heat system is turned on, current flows through a conductive heating material. For high-voltage radiant heat systems, line voltage (110 V or 230 V) current flows through the heating cable. For low-voltage systems, the line voltage is converted to low voltage (8 to 30 V) in the control unit (which contains a step-down transformer) and this low voltage is then applied to the heating element.
The heated material then heats the flooring until it reaches the right temperature set by the floor thermostat. The flooring then heats the adjacent air, which circulates, heating other objects in the room (tables, chairs, people) by convection. As it rises, the heated air will heat the room and all its contents up to the ceiling. This form of heating gives the most consistent room temperature from floor to ceiling compared to any other heating system.
Thursday, February 8, 2007
Fixed Resistors
Some resistors are cylindrical, with the actual resistive material in the center (composition resistors, now obsolete) or on the surface of the cylinder (film) resistors, and a conducting metal lead projecting along the axis of the cylinder at each end(axial lead). There are carbon film and metal film resistors. The photo above right shows a row of common resistors. Power resistors come in larger packages designed to dissipate heat efficiently. At high power levels, resistors tend to be wire wound types.
Resistors used in computers and other devices are typically much smaller, often in surface-mount packages without wire leads. Resistors can also be built into integrated circuits as part of the fabrication process, using the semiconductor material as a resistor. But resistors made in this way are difficult to fabricate and may take up a lot of valuable chip area, so IC designers alternatively use a transistor-transistor or resistor-transistor configuration to simulate the resistor they require.
All wire except superconducting wire has some resistance, depending on its cross-sectional area and the conductivity of the material it is made of. Resistance wire has an accurately known resistance per unit length, and is used to make wire-wound resistors.
Resistors used in computers and other devices are typically much smaller, often in surface-mount packages without wire leads. Resistors can also be built into integrated circuits as part of the fabrication process, using the semiconductor material as a resistor. But resistors made in this way are difficult to fabricate and may take up a lot of valuable chip area, so IC designers alternatively use a transistor-transistor or resistor-transistor configuration to simulate the resistor they require.
All wire except superconducting wire has some resistance, depending on its cross-sectional area and the conductivity of the material it is made of. Resistance wire has an accurately known resistance per unit length, and is used to make wire-wound resistors.
Units of Resistor
The SI unit of electrical resistance is the ohm (Ω). A component has a resistance of 1 Ω if a voltage of 1 volt across the component results in a current of 1 ampere, or amp, which is equivalent to a flow of one coulomb of electrical charge (approximately 6.241506 × 1018 electrons) per second. The multiples kiloohm (1 kΩ = 1000 Ω) and megaohm (1 MΩ = 106 Ω) are also commonly used.
In an ideal resistor, the resistance remains constant regardless of the applied voltage or current through the device or the rate of change of the current. Whereas real resistors cannot attain this goal, they are designed to present little variation in electrical resistance when subjected to these changes, or to changing temperature and other environmental factors.
In an ideal resistor, the resistance remains constant regardless of the applied voltage or current through the device or the rate of change of the current. Whereas real resistors cannot attain this goal, they are designed to present little variation in electrical resistance when subjected to these changes, or to changing temperature and other environmental factors.
Resistor
A resistor is a two-terminal electrical or electronic component that resists an electric current by producing a voltage drop between its terminals in accordance with Ohm's law. : The electrical resistance is equal to the voltage drop across the resistor divided by the current through the resistor. Resistors are used as part of electrical networks and electronic circuits.
A resistor is used to create a known voltage-to-current ratio in an electric circuit. If the current in a circuit is known, then a resistor can be used to create a known potential difference proportional to that current. Conversely, if the potential difference between two points in a circuit is known, a resistor can be used to create a known current proportional to that difference. Current-limiting.
By placing a resistor in series with another component, such as a light-emitting diode, the current through that component is reduced to a known safe value. A series resistor can be used for speed regulation of DC motors, such as used on locomotives and trainsets. An attenuator is a network of two or more resistors (a voltage divider) used to reduce the voltage of a signal.
A line terminator is a resistor at the end of a transmission line or daisy chain bus (such as in SCSI), designed to match impedance and hence minimize reflections of the signal. All resistors dissipate heat. This is the principle behind electric heaters. (See also electric heating and resistive heating)
A resistor is used to create a known voltage-to-current ratio in an electric circuit. If the current in a circuit is known, then a resistor can be used to create a known potential difference proportional to that current. Conversely, if the potential difference between two points in a circuit is known, a resistor can be used to create a known current proportional to that difference. Current-limiting.
By placing a resistor in series with another component, such as a light-emitting diode, the current through that component is reduced to a known safe value. A series resistor can be used for speed regulation of DC motors, such as used on locomotives and trainsets. An attenuator is a network of two or more resistors (a voltage divider) used to reduce the voltage of a signal.
A line terminator is a resistor at the end of a transmission line or daisy chain bus (such as in SCSI), designed to match impedance and hence minimize reflections of the signal. All resistors dissipate heat. This is the principle behind electric heaters. (See also electric heating and resistive heating)
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