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.
Showing posts with label Resistors. Show all posts
Showing posts with label Resistors. Show all posts
Thursday, February 8, 2007
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)
Monday, January 8, 2007
Terminology for Televisions
Pixel resolution is the amount of individual points known as pixels on a given screen. A typical resolution of 720x480 means that the television display has 720 pixels across and 480 pixels on the vertical axis. The higher the resolution on a specified display the sharper the image. Contrast ratio is a measurement of the range between the brightest and darkest points on the screen. The higher the contrast ratio, the better looking picture there is in terms of richness, deepness, and shadow detail.
The brightness of a picture measures how vibrant and impacting the colors are. Measured in cd / m2 equivalent to the amount of candles required to power the image.
On the other hand, the so-called brightness and contrast adjustment controls on televisions and monitors are traditionally used to control different aspects of the picture display. The brightness control shifts the black point, or shadow level, primarily affecting the contrast ratio or gamma of the image, while the contrast control primarily controls the image intensity or brightness.
The brightness of a picture measures how vibrant and impacting the colors are. Measured in cd / m2 equivalent to the amount of candles required to power the image.
On the other hand, the so-called brightness and contrast adjustment controls on televisions and monitors are traditionally used to control different aspects of the picture display. The brightness control shifts the black point, or shadow level, primarily affecting the contrast ratio or gamma of the image, while the contrast control primarily controls the image intensity or brightness.
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