ECONMT 115 - CH5 - Resistors

Short circuit (1)

A branch in a circuit with zero or very low resistance, as a result a large amount of amperes could flow.

Variable resistors (3)

1. Are known by several common names. The most popular name is pot, which is shortened from the word potentiometer. 2. A potentiometer is a variable resistor that has three terminals. 3. Potentiometers can be used as rheostats by using only two of their three terminals.

Wire-wound resistors (5)

1. Can be found in various case styles and sizes. These resistors are generally used when a high power rating is needed. 2. Wire-wound resistors can operate at higher temperatures than any other type of resistor. 3. This type of resistor should be mounted vertically and not horizontally. 4. This increase of airflow dissipates heat at a faster rate to help keep the resistor from overheating. 5. They are expensive and generally require a large amount of spacefor mounting. They can also exhibit an amount of inductance in circuits that operate at high frequencies. This added inductance can cause problems for the rest of the circuit.

Metal film resistors are (4)

1. Constructed by applying a film of metal to a ceramic rod in a vacuum (Figure 5-5). 2. The resistance is determined by the type of metal used to form the film and the thickness of the film. 3. Typical thicknesses for the film are from 0.00001 to 0.00000001 inch. 4. Leads are then attached to the film coating and the entire assembly is covered with a coating.

Wire-Wound Resistors (3)

Fixed resistors that are made by winding a piece of resistive wire around a ceramic core (Figure 5-6). The resistance of a wire-wound resistor is determined by three factors: 1. The type of material used to make the resistive wire 2. The diameter of the wire 3. The length of the wire

Voltage divider (1)

The second principal function of resistors is to produce this.

Variable resistor (2)

1. A resistor whose values can be changed or varied over a range. 2. Variable resistors can be obtained in different case styles and power ratings.

Standard Resistance Values of Fixed Resistors (2)

1. Fixed resistors are generally produced in standard values. 2. The higher the tolerance value, the fewer resistance values available.

Rheostat (2)

1. Is actually a variable resistor that has two terminals. 2. They are used to adjust the current in a circuit to a certain value.

Carbon Resister vs Metal Film Resistor (4)

1. Metal film resistors do not change their value with age, and their tolerance is generally better than that of carbon resistors. 2. Tolerance indicates the plus and minus limits of a resistor's ohmic value. 3. Carbon resistors commonly have a tolerance range of 20%, 10%, or 5%. Metal film resistors generally range in tolerance from 2% to 0.1%. 4. The disadvantage of the metal film resistor is that it costs more.

Fixed resistors have only one (2)

1. Ohmic value, which cannot be changed or adjusted. 2. There are several different types of fixed resistors.

Composition carbon resistor (4)

1. One of the most common types of fixed resistors is this one. 2. These are made from a compound of carbon graphite and a resin bonding material. 3. The proportions of this and resin material determine the value of resistance. 4. This compound is enclosed in a case of non-conductive material with connecting leads.

Resistors are (Mathematically)

1. One of the primary types of electric loads, and electrical theory can be applied through the use of resistors in such formulas as Ohm's law. 2. This concept is required when calculating field requirements and controlling heat in a circuit.

Power Ratings (2)

1. Resistors also have a power rating in watts that should not be exceeded or the resistor will be damaged. 2. The amount of heat that must be dissipated by (given off to the surrounding air) the resistor can be determined by the use of one of the Power formulas.

Resistors are one of the most common components found in electric circuits. Unit, Symbol, Packaging (3)

1. The unit of measure for resistance (R) is the ohm, which was named for a German scientist named Georg S. Ohm. 2. The symbol used to represent resistance is the Greek letter omega (V). 3. Resistors come in various sizes, types, and ratings to accommodate the needs of almost any circuit applications.

Color code (2)

1. The value of a resistor can often be determined by this. 2. The bands of color that are used to determine the resistance value, tolerance, and in some cases reliability.

Carbon resistors are very popular for most applications because (3)

1. They are inexpensive and readily available. 2. They are made in standard values that range from about 1 ohm to about 22 megohms (MV), and they can be obtained in power ratings of 1⁄8, ¼, ½, 1, and 2 watts. 3. The power rating of the resistor is indicated by its size. 4. Carbon resistors will change their value with age or if they are overheated. 5. Carbon resistors generally increase instead of decrease in value.

Carbon Film Resistors

1. This resistor is made by coating a ceramic rod with a film of carbon instead of metal. 2. Carbon film resistors are less expensive to manufacture than metal film resistors and can have a higher tolerance rating than composition carbon resistors.

Metal Glaze Resistors

1. This resistor is made by combining metal with glass. The compound is then applied to a ceramic base as a thick film. 2. The resistance is determined by the amount of metal used in the compound. 3. Tolerance ratings of 2% and 1% are common.

Series Circuit (Resistivity) (2)

1. Voltage is Additive. 2. By connecting resistors of the proper value, almost any voltage desired can be obtained.