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Navy Electricity and Electronics Training Series (NEETS)
Module 1—Introduction to Matter, Energy, and Direct Current
Chapter 1:  Pages 1-51 through 1-60

[Go to TOC]




 

Compass and bar magnet - RF Cafe





Earth's magnetic field - RF Cafe

 




The NORTH POLE, or north seeking pole, a magnet freely suspended on a string always points toward the north geographical pole.

The LIKE POLES magnets repel each other, while the unlike poles attract each other.
 

1-51




WEBER’S THEORY of MAGNETISM assumes that all magnetic material is made up magnetic molecules which, if lined up in north to south pole order, will be a magnet. If not lined up, the magnetic fields about the molecules will neutralize each other and no magnetic effect will be noted.


Magnetizing a bar - RF Cafe



The DOMAIN THEORY of MAGNETISM states that if the electrons the atoms in a material spin more in one direction than in the other, the material will become magnetized.


Magnetic field electron - RF Cafe



A MAGNETIC FIELD is said to exist in the space surrounding a magnet.
 

1-52




Magnetic lines of force - RF Cafe



MAGNETIC LINES of FORCE are imaginary lines used to describe the patterns the magnetic field about a magnet. These lines are assumed to flow externally from the north pole and into the south pole.


Magnetic lines of force - RF Cafe



MAGNETIC FLUX is the total number magnetic lines force leaving or entering the pole a magnet.
 

1-53




Magnetic flux lines - RF Cafe



FLUX DENSITY is the number flux lines per unit area.

FIELD INTENSITY or the intensity a magnetic field is directly related to the magnetic force exerted by the field.

The INTENSITY ATTRACTION/REPULSION between magnetic poles may be described by a law almost identical to Coulomb’s Law Charged Bodies, that is, the force between two poles is directly proportional to the product the pole strengths and inversely proportional to the square the distance between the poles.

MAGNETIC SHIELDING can be accomplished by placing a cast iron shield around the object to be protected, thus directing the lines force around the object.
 

1-54




Magnetic Shielding using iron - RF Cafe



MAGNETS are CLASSIFIED by SHAPE and include the bar magnet, the horseshoe magnet, and the ring magnet. The ring magnet is used in computer memory circuits; the horseshoe magnet in some meter circuits.

ENERGY may be defined as the ability to do work.



The COULOMB (C) is the basic unit used to indicate an electrical charge. One coulomb is equal to a charge 6.28 x 1018  electrons. When one coulomb charge exists between two bodies, the electromotive force (or voltage) is one volt.

VOLTAGE is measured as the difference potential two charges interest.

VOLTAGE MEASUREMENTS may be expressed in the following units: volts (V), kilovolts (kV), millivolts (mV), or microvolts (μV).

For example:

1 kV  = 1,000 V

1 mV = 0.001 V

1  V  = 0.000001 V


METHODS of PRODUCING a VOLTAGE include:


1.  Friction

2.  Pressure (piezoelectricity)
 

1-55




Piezoelectricity




3.  Heat (thermoelectricity)


Thermoelectricity - RF Cafe

 


 

1-56




4.  Light (photoelectricity)


Photoelectricity - RF Cafe



5.  Chemical action (battery)
 

1-57




Chemical reaction electricity - RF Cafe



6.  Magnetism (electromagnetic induction generator)

ELECTROMAGNETIC INDUCTION GENERATOR To produce voltage by use magnetism, three conditions must be met: There must be a CONDUCTOR in which the voltage will be produced; there must be a MAGNETIC FIELD in the conductor’s vicinity; and there must be relative motion between the field and conductor. When these conditions are met, electrons WITHIN THE CONDUCTOR are propelled in one direction or another, creating an electromotive force, or voltage.


Electromagnetic induction generator - RF Cafe

 


 

1-58




ELECTRON CURRENT is based on the assumption that electron current flow is from negative to positive through a circuit.

An ELECTRIC CURRENT is a directed movement electrons in a conductor or circuit.
 
The AMPERE is the basic unit used to indicate an electric current. A current one ampere is said to flow when one coulomb charge (6.28 x 1018  electrons) passes a given point in one second time. Current measurements may be expressed in the following units: ampere (A), milliampere (mA), and microampere (μA). Current in a circuit increases in direct proportion to the voltage (emf) applied across the circuit.

RESISTANCE is the opposition to current. The ohm is the basic unit resistance and is represented by the Greek letter omega (Ω). A conductor is said to have one ohm resistance when an emf one volt causes one ampere current to flow in the conductor. Resistance may be expressed in the following units: ohm (Ω), kilohm (kΩ), and megohms (MΩ). For example, 1,000,000 Ω  = 1,000 kΩ  = 1 MΩ.

The RESISTANCE of a MATERIAL is determined by the type, the physical dimensions, and the temperature the material that is,

1.  A good conductor contains an abundance free electrons.

2.  As the cross-sectional area a given conductor is increased, the resistance will decrease.

3.  As the length a conductor is increased, the resistance will increase.

4.  In a material having a positive temperature coefficient, the resistance will increase as the temperature is increased.

The CONDUCTANCE of a MATERIAL is the reciprocal resistance.

The UNIT of CONDUCTANCE is the mho and the symbol is V. G or S.

The RESISTOR is manufactured to provide a specific value resistance.
 

1-59




The CARBON RESISTOR is made carbon, with fillers and binders blended in to control the ohmic value.

Resistor types - RF Cafe



The RESISTANCE of a WIREWOUND RESISTOR is determined by the metal content the wire and the wire’s length. Wirewound resistors may be tapped so two or more different voltage values may be taken f the same resistor.


Resistor symbols - RF Cafe



 

1-60





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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