Multimedia Speakers

Computer speakers, or multimedia speakers, are external speakers and are usually equipped with a male 1/8 inch stereo jack plug (usually color-coded lime green per the PC 99 standard) for computer sound cards.

However, some have an RCA connector, and some people connect the output of their computer sound cards to a conventional stereo system.

There are also USB speakers which are powered from the 5 volts at a few milliamsp provided by the USB port, per the standard. Computer speakers are usually a simplified stereo system without a radio or other media sources built in.

Computer speakers range widely in quality and in price. Typically, the computer speakers packaged with computer systems are both small and simple. There are also advanced forms of computer speakers that have graphic equalization features (bass, treble, etc.) and sometimes built-in amplifiers.

It is common to connect active/powered computer speakers to a power strip. The power outlet should, as always, preferably be grounded for safety.

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.

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.