Download Chapter 4 * Circuit Components

Chapter 4 – Circuit Components
Chapter Objectives
1. Identify common electric components and their schematic
symbols.
2. Measure and specify wire size for electric conductors.
3. Understand the operating principles of electric components.
4. Interpret and specify the ratings of components.
5. Understand the terminology used to describe circuit components
and faults.
6. Use the resistor color code to determine resistance and tolerance.
You will examine in depth…
 Types of Batteries and Cells
 Miniature Lamps and LEDS
 Resistors
 Switches
 Wires and Cables
 Fuses
Batteries and Cells
 Unless otherwise specified, the terms cell and battery refer to
the electric chemical type.
 A cell is a electrochemical device consisting of two electrodes
made of different materials and an electrolyte.
 The chemical reaction between the electrodes and the
electrolyte produces a voltage.
 A battery consists of two or more cells electrically connected
together and packaged as a single unit.
 The term battery is often used to indicate either a single cell or a
group of cells.
Cells and Batteries
 Cells and batteries are classified as either primary or
secondary.
 Primary cells are not rechargeable.
 The chemical reaction within the cells is not easily reversed.
 When all of the chemicals are used in a reaction, the cell is fully
discharged.
 Secondary cells may be discharged and charged many times.
 The number of times a cell may be discharged and charged
depends on the type and size of the cell and on the operating
conditions.
Batteries and Cells
 Cells and batteries are also classified as dry or wet.
 Historically, a dry cell was one that had a paste or gel
electrolyte and was semi-sealed.
 A dry cell refers to a cell that can be operated in any position
without electrolyte leakage.
 Wet cells must be operated in an upright position.
 Have vents to allow gases generated during charge or discharge
to escape.
 Most common is a lead-acid cell.
How a battery actually works!
 All batteries have two terminals, one marked
positive (+) and one marked negative (-).
 Electrons collected on the negative terminal
of the battery travel through a load and back
to the positive terminal as fast as they can.
 A chemical reaction produces the electrons.
The speed of electron production by this
chemical reaction (the battery's internal
resistance) controls how many electrons can
flow between the terminals.
 Once you connect a wire, the reaction starts.
The ability to harness this sort of reaction
started with the voltaic pile.
The Voltaic Pile
 The first battery was created by
Alessandro Volta in 1800.
 This arrangement was known as a
voltaic pile. The top and bottom
layers of the pile must be different
metals. If you attach a wire to the
top and bottom of the pile, you can
measure a voltage and a current
from the pile.
 The pile can be stacked as high as
you like, and each layer will increase
the voltage by a fixed amount.
The Lead-Acid Battery
 The cell has one plate made of lead and another
plate made of lead dioxide, with a strong sulfuric acid
electrolyte in which the plates are immersed.
 Lead combines with SO4 (sulfate) to create PbSO4
(lead sulfate), plus one electron.
 Lead dioxide, hydrogen ions and SO4 ions, plus
electrons from the lead plate, create PbSO4 and
water on the lead dioxide plate.
 As the battery discharges, both plates build up PbSO4
and water builds up in the acid. The characteristic
voltage is about 2 volts per cell, so by combining six
cells you get a 12-volt battery.
 A lead-acid battery has a nice feature -- the reaction
is completely reversible. If you apply current to the
battery at the right voltage, lead and lead dioxide
form again on the plates so you can reuse the battery
over and over.
Resistors
 One of the most common and most reliable electric-electronic
components is the resistor.
 The resistor is used as a load, or part of the load, in most
electronic circuits.
 Its major purposes are to control current and divide voltage.
 Some types of resistors can operate at temperatures as high as
300°C or (572°F). Resistors can become very HOT!
 Resistances of less than 1Ωto more than 100 MΩ are available.
Resistor Identification
 A color-coded strip system is used to display a resistor’s value.
 Based of the Electronic Industries Association (EIA).
 Meaning is as follows:
 First Band, closest to the end, represents the first digit.
 Second Band, represents the second digit.
 Third Band, represents the number of zeros added to the first two
digits.
 Fourth Band, represents the tolerance of the resistor.
Resistor Identification