Color Band Resistors

Define the following:

RESISTOR

A resistor is a component of a circuit that resists the flow of electrical current. It has two terminals across which electricity must pass, and it is designed to drop the voltage of the current as it flows from one terminal to the other. Resistors are primarily used to create and maintain known safe currents within electrical components.

Resistors are coated with paint or enamel, or covered in molded plastic to protect them. Because they are often too small to be written on, a standardized color-coding system is used to identify them. The first three colors represent ohm value, and a fourth indicates the tolerance, or how close by percentage the resistor is to its ohm value. This is important for two reasons: the nature of its construction is imprecise, and if used above its maximum current, the value can change or the unit itself can burn up.

• RESISTANCE

In physics, resistance is defined as the ability of a substance to prevent or resist the flow of electrical current. A substance resists electrical current because of a collision between electrons and atoms, which slows the electrons down and converts some of their energy to heat energy. In some cases, the energy is also converted into light.

German physicist Georg Ohm (1789-1854) is credited with discovering the effect of a material's make up, length and thickness on its resistance. In fact, the standard unit of measuring resistance, the ohm, is named after him. Ohm's law became publicly known in 1827 and states that a circuit’s resistance is 1 ohm if a 1-volt voltage make 1 amp of current. According to Ohm's law, a circuit's resistance is equal to its voltage divided by the amount of current.

• RESISTIVITY

The measure of the potential electrical resistance of a conductive material. It is determined experimentally using the equation [pic] = RA/l, where R is the measured resistance of some length of the material, A is its cross-sectional area (which must be uniform), and l is its length. It is measured in ohm-meters.

Resistivity of a material remains constant whether it is taken about 1 cm.....or 1km... (on a constant temperature and other physical conditions remains the same)

The Resistivity of a material depends on temperature( and other physical conditions such as air pressure) and the nature of the material (avaibility of free electrons....number of free electrons are same in an element atoms).

• TEMPERATURE COEFFICIENT

The temperature coefficient is the relative change of a physical property when the temperature is changed by 1 Kelvin.

In the following formula, let R be the physical property to be measured and T be the temperature at which the property is measured. T0 is the reference temperature, and ΔT is the difference between T and T0. Finally, α is the (linear) temperature coefficient. Given these definitions, the physical property is:

[pic] Here α has the dimensions of an inverse temperature (1/K or K−1).

This equation is linear with respect to temperature. For quantities that vary polynomially or logarithmically with temperature, it may be possible to calculate a temperature coefficient that is a useful approximation for a certain range of temperatures. For quantities that vary exponentially with temperature, such as the rate of a chemical reaction, any temperature coefficient would be valid only over a very small temperature range.

Different temperature coefficients are specified for various applications, including nuclear, electrical and magnetic.

1. What are the uses of resistors?

• Resistors are essential in electronic circuits, as they control the amount of current that runs through them. Without resistors voltage would be too great for individual components to handle and would result in overloading or destruction.

The principle by which resistors work can also be applied to heating elements in irons, toasters, heaters, electric stoves and hair dryers, which dissipate voltage as heat. Variable resistors may function as sensors, switches or voltage dividers. Specialist end uses, such as new generation automotive LED light clusters, demand a specialist resistor solution. Aluminum clad wire wound resistors provide high power dissipation in a limited space, and are designed for direct heat sink mounting, using thermal compound to achieve maximum performance. The resistors work as a ballast to augment the resistance in the LED, mimicking that of a conventional

2. What is the difference between 4 color, 5 color, and 6 color band resistors?

• 4 Color Band Resistors- These resistors have two bands for the resistance value and 1 band for the multiplier and 1 tolerance band. This is the most common variation.

• 5 Color Band Resistors- These are with high precision and have an extra band to indicate a 3rd significant digit. The 1st three bands indicate the significant digits, the 4th band is the multiply factor and the 5th represents the tolerance. There are exceptions to this. For example, sometimes the extra band indicates failure rate or temperature coefficient.

• 6 Color Band Resistors- These are resistors that are usually for high precision that have an additional band to specify the temperature coefficient (ppm/k). The 1st three bands are for the resistance value, the 4th for the multiplier, the 5th for the tolerance and the 6th for the temperature coefficient.

Sources: http://www.wisegeek.com/what-is-a-resistor.htm http://www.wisegeek.com/in-physics-what-is-resistance.htm http://in.answers.yahoo.com/question/index?qid=20100627073410AAvDj3T http://www.thefreedictionary.com/resistivity http://en.wikipedia.org/wiki/Temperature_coefficient http://www.rapidonline.com/infozone/resistors/applications.htm