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Navy Electricity and Electronics Training Series (NEETS)
Module 1—Introduction to Matter, Energy, and Direct Current
Chapter 3:  Pages 3-111 through 3-120

[Go to TOC]




Q59.  Is it considered safe for a person to touch any energized low-voltage conductor with the bare hand?

Q60.  What should you do if you become aware a possible malfunction in a piece electrical equipment?

Q61.  Who should perform CPR?

SUMMARY

With the completion this chapter you have gained a basic understanding dc circuits. The information you have learned will provide you with a firm foundation for continuing your study electricity. The following is a summary the important points in the chapter.

A BASIC ELECTRIC CIRCUIT consists a source electrical energy connected to a load. The load uses the energy and changes it to a useful form.

Basic electric circuit - RF Cafe



A SCHEMATIC DIAGRAM is a “picture“ a circuit, which uses symbols to represent components. The space required to depict an electrical or electronic circuit is greatly reduced by the use a schematic.
 

3-111




Schematic symbols - RF Cafe



VOLTAGE (E) is the electrical force or pressure operating in a circuit.

An AMPERE (A) represents the current flow produced by one volt working across one ohm resistance.

RESISTANCE (R) is the opposition to current. It is measured in ohms (  ). One ohm resistance will limit the current produced by one volt to a level one ampere.
 
The OHM’S FORMULA can be transposed to find one the values in a circuit if the other two values are known. You can transpose the Ohm’s law formula

Ohm's Law Formula - RF Cafe



mathematically, or you can use the Ohm’s law figure to determine the mathematical relationship between R, E, and l.
 

3-112




Ohm's Law - RF Cafe



GRAPHICAL ANALYSIS the relationship between R, E, and I can be studied by plotting these quantities on a graph. Such a graph is useful for observing the characteristics an electrical device.


Graphical circuit analysis - RF Cafe



POWER is the rate doing work per unit time. The time required to perform a given amount work will determine the power expended. As a formula, P = E x I, where P = power in watts, E = voltage in volts, and I = current in amperes.

The FOUR BASIC ELECTRICAL QUANTITIES are P, I, E, R. Any single unknown quantity can be expressed in terms any two the other known quantities. The formula wheel is a simple representation these relationships.
 

3-113




Ohm's Law wheel - RF Cafe




POWER RATING in watts indicates the rate at which a device converts electrical energy into another form energy. The power rating a resistor indicates the maximum power the resistor can withstand without being destroyed.

POWER USED by an electrical device is measured in watt-hours. One watt-hour is equal to one watt used continuously for one hour.



The EFFICIENCY an electrical device is equal to the electrical power converted into useful energy divided by the electrical power supplied to the device.

Efficiency Formula - RF Cafe



HORSEPOWER is a unit measurement ten used to rate electrical motors. It is a unit work. One horsepower is equal to 746 watts.

A SERIES CIRCUIT is defined as a circuit that has only one path for current flow.
 

3-114




Basic series circuit - RF Cafe



RULES for SERIES DC CIRCUITS:

.         The same current flows through each part a series circuit.

.         The total resistance a series circuit is equal to the sum the individual resistances.

.         The total voltage across a series circuit is equal to the sum the individual voltage drops.

.         The voltage drop across a resistor in a series circuit is proportional to the ohmic value the
          resistor.

.         The total power in a series circuit is equal to the sum the individual power used by each
          circuit component.

Kirchhoff's VOLTAGE LAW states: The algebraic sum the voltage drops in any closed path in a circuit and the electromotive forces in that path is equal to zero, or Ea  + Eb + Ec  +...En  = 0.
 

3-115




Kirchhoff's Voltage Law - RF Cafe



VOLTAGE POLARITIES must be used when applying Kirchhoff's voltage law. The point at which current enters a load (resistor) is considered negative with respect to the point at which current leaves the load.

SERIES AIDING VOLTAGES cause current to flow in the same direction; thus the voltages are added.

Series aiding and series opposing voltages - RF Cafe



SERIES OPPOSING VOLTAGES tend to force current to flow in opposite directions; thus the equivalent voltage is the difference between the opposing voltages.

A REFERENCE POINT is a chosen point in a circuit to which all other points are compared.
 

3-116




Voltage reference point - RF Cafe



An OPEN CIRCUIT is one in which a break exists in the complete conducting pathway.

A SHORT CIRCUIT is an accidental path low resistance which passes an abnormally high amount current.

INTERNAL RESISTANCE causes a drop in the terminal voltage a source as current flows through the source. The decrease in terminal voltage is caused by the voltage drop across the internal resistance. All sources electromotive force have some form internal resistance.

Internal resistance - RF Cafe


 

3-117




HIGH EFFICIENCY in a circuit is achieved when the resistance the load is high with respect to the resistance the source.

Electrical circuit efficiency - RF Cafe


 

3-118




POWER TRANSFER in a circuit is highest when the resistance the load equals the resistance the source.

A PARALLEL CIRCUIT is a circuit having more than one current path connected to a common voltage source.

Parallel circuit - RF Cafe



RULES for PARALLEL DC CIRCUITS:

.         The same voltage exists across each branch a parallel circuit and is equal to the source
          voltage.

.         The current through a branch a parallel network is inversely proportional to the amount
          resistance the branch.

.         The total current a parallel circuit is equal to the sum the currents the individual
          branches the circuit.

.         The total resistance a parallel circuit is equal to the reciprocal the sum the reciprocals
          the individual resistances the circuit.

.         The total power consumed in a parallel circuit is equal to the sum the power consumptions
          the individual resistances.

The SOLUTION A COMBINATION CIRCUIT is a matter applying the laws and rules for series and parallel circuits as applicable.
 

3-119




Combination series parallel circuits  - RF Cafe



ALL PARALLEL CIRCUITS ARE COMBINATION CIRCUITS when the internal resistance the source is taken into account.

REDRAWING CIRCUITS for CLARITY is accomplished in the following steps:

1.   Trace the current paths in the circuit.

2.   Label the junctions in the circuit.

3.   Recognize points which are at the same potential.

4.   Visualize rearrangements, “stretching“ or “shrinking,“ connecting wires.

5.   Redraw the circuit into simpler form (through stages if necessary).
 

3-120




Introduction to Matter, Energy, and Direct Current, Introduction to Alternating Current and Transformers, Introduction to Circuit Protection, Control, and Measurement, Introduction to Electrical Conductors, Wiring Techniques, and Schematic Reading, Introduction to Generators and Motors, Introduction to Electronic Emission, Tubes, and Power Supplies, Introduction to Solid-State Devices and Power Supplies, Introduction to Amplifiers, Introduction to Wave-Generation and Wave-Shaping Circuits, Introduction to Wave Propagation, Transmission Lines, and Antennas, Microwave Principles, Modulation Principles, Introduction to Number Systems and Logic Circuits, Introduction to Microelectronics, Principles of Synchros, Servos, and Gyros, Introduction to Test Equipment, Radio-Frequency Communications Principles, Radar Principles, The Technician's Handbook, Master Glossary, Test Methods and Practices, Introduction to Digital Computers, Magnetic Recording, Introduction to Fiber Optics

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