Uses of Resistors

What would the maximum and minimum allowable ohm values be for an 5.0 MΩ ±20% resistor?

Maximum = 6.0 MΩ Minimum = 4.0 MΩ

Multiturn variable resistors

Multiturn variable resistors operate by moving the wiper arm with a screw of some number of turns. They generally range from 3 turns to 10 turns

Can rheostats be connected to work like a potentiometer?

No

The amount of opposition a resistor gives to the flow of current is measured in _____.

Ohms

Unit of measurement

Ohms, Ω.

Composition carbon resistor

One of the most common types of fixed resistors

the power rating for a composition resistor is determined by

Physical size

Temperture

Positive Temperature - DIRECTLY proportional Negative Temperature - INVERSELY proportional

Symbol for Resistor

R

The opposition to current flow is called _____.

Resistance

An electronic component whose purpose is to limit current flow is called the _____.

Resistor

Rheostat

Rheostatis actually a variable resistor that has to turn

the markings on a fixed wire wound resistor will include

power rating and ohmic value

What would the maximum and minimum allowable ohm values be for an 25 KΩ ±5% resistor?

Maximum = 26.250 KΩ Minimum = 23.750 KΩ

fixed resistors are resistors that have their ohmic value constant true or false?

true

Metal Film

*Applications* 1. For circuits that require accuracy. *Advantages* 1. Accurate 2. not frequency sensitive *Disadvantages* 1. more expensive than carbon composition resistors but cheaper than wire-wound resistor

Carbon Film or Cracked Carbon Resistor

*Applications* 1. General purpose *Advantages* 1. Cheap 2. Stable *Disadvantages* 1. generate noise

Carbon Composition

*Applications* 1. General purpose *Advantages* 1. Cheap 2. not frequency sensitive 3. easily available *Disadvantages* 1) value changes with time and temperature 2) generate noise

Wire-wound

*Applications* For circuits that require: high current, high power and high accuracy. *Advantages* 1. accurate 2. stable with time and temperature *Disadvantages* 1) expensive 2) frequency sensitive 3) low ohmic values 4) bulky

Symbol for a potentiometer.

...

Types of Fixed-value Resistors

1. Carbon Composition 2. Carbon Film 3. Metal Film 4. Wire-wound

Factors affecting of the resistance of a resistor at constant temperature

1. length (l) of conductor 2. cross-sectional area ( A ) of the conductor 3. material used.

What is the value and tolerance of a resistor with the following color code: Red Yellow Blue Gold

24 MΩ ±5%

What is the value and tolerance of a resistor with the following color code: Blue Black Orange Silver

60 KΩ ±10%

potentiometer

A potentiometer is a variable resistor used as a voltage divider

Fixed

A set value that does not change.

Varible

Adjustable value that can change as the component is in use.

Tapped

Allows different values, a maximum and below. Kills power first before adjustment.

The Coloured bands of a resistor are arranged and "read" closest to the.

Left end and read 'left to right'

Carbon resistor

Carbon film resistors are less expensive to manufacture than metal film resistors and can have a higher tolerance rating than composition carbon resistors

Carbon resistors

Carbon resistors are very popular for most applications because they are inexpensive and readily available

Carbon resistors

Carbon resistors will change their value with age or if they are overheated. Carbon resistors generally increase instead of decrease in value

The ohm value of small wattage fixed value resistors is typically shown by the use of a ________.

Color code

Resistor

Components that provide measured amounts of opposition to the current.

Rheostats vary circuit _____.

Current

Factors that affect resistors;

Material, Length, cross section, and temperature.

the two categories of resistors are

Fixed and variable

wire round resistors are manufactures for use in circuits as

Fixed and variable ohmic value

Two broad category of resistors are;

Fixed value Variable value

Types of Resistors

Fixed, Tapped, and Variable.

A resistor's wattage rating is related to;

How much power it can dissipate in the form of heat.

Current Divider Formula

I1 = R2 divided by R1+R2 times I total I2 = R1 divided by R1+R2 times I total

Material

Some material offers more resistance than others.

Length

The longer the conductor the more resistance it has. Resistance varies DIRECTLY with the length of the wire.

Cross sectional area

The smaller the diameter is the more resistance it has. INVERSELY proportional to resistance. Coffee straw in milkshake analogy.

Metal film resistors

These resistors are superior to carbon resistors in several respects. Metal film resistors do not change their value with Age, and their tolerance is generally better than carbon resistors • The disadvantage is the metal film resistor is that it costs more

Variable Resistors

They are used as volume, bass and treble controls of audio amplifiers, the brightness. Example: potentiometer, rheostat and preset.

Potemitor

Used to control voltage. Ex) Car radio

Potentiometers and rheostats are two types of ____.

Variable resistor

Variable resistors

Variable resistors can change their value within the limit of their full value

Rehosta

Varies current flow. Ex) A dim switch

Potentiometers vary ____.

Voltage .... they act as variable voltage dividers.

The physical size of a resistor is directly related to its _____.

Wattage rating

Wire-wound

Wire-wound resistors can operate at higher temperatures than any other type of resistor

Can potentiometers be connected to work like rheostats?

Yes

the ohmic value of most composition resistors is given by

a color code

under proper operating conditions a resistor, of any type, should never get hot enough to be 'hot to the touch' true or false?

false

where are wire wound resistors often used?

high power rating applications

a commonly used resistor code system is

letters

what type of coating is placed on a film resistor?

silicone or laquer

the tolerance of a resistor relates to

the variance of indicated ohmic value

What is the tolerance of a resistor without a forth gold or silver band?

±20%

Wired-wound resistors is determined by three factors

• The type of material used to make the resistive wire • The diameter of the wire • The length of the wire

And adjustable wire-wound resistor that has a hollow center

• advantages ( this increases a airflow dissipates heat at a faster rate to help keep the resistor from overheating) • disadvantage ( they are expensive and generally requires a large amount of space for mounting)

Fixed resistors

• composition carbon • Metal film • carbon film • Metal glaze • wire-wound