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Chapter 4 – Circuit Components

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1 Chapter 4 – Circuit Components
Chapter Objectives Identify common electric components and their schematic symbols. Measure and specify wire size for electric conductors. Understand the operating principles of electric components. Interpret and specify the ratings of components. Understand the terminology used to describe circuit components and faults. Use the resistor color code to determine resistance and tolerance.

2 You will examine in depth…
Types of Batteries and Cells Miniature Lamps and LEDS Resistors Switches Wires and Cables Fuses

3 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.

4 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.

5 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.

6 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.

7 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.

8 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.

9 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.

10 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.

11 Resistor Identification

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