MODULE V
Electrical engineering - Basics Page 6

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1.2.2 Characteristics of the components of atoms

Characteristics of the components of atoms
Component
Symbol
Charge
Mass
Mass ratio
Proton
p
positive
1,7 * 10ˆ-24g
1
Neutron
n
neutral
1,7 * 10ˆ-24g
1
Electron
e-
negative
9,1 * 10ˆ-28g
1/2000



1.3 The electric current

Unit of measurement
A
Ampere
(André-Marie Ampere, French Physicist, 1775-1836)
Unit symbol
I
Amperage


The electric current indicates how many electrons flow through the cross-section of a conductor per unit of time. If 6,25 * 10ˆ18 electrons per second flow through a conductor cross-section a current of 1 Ampere is flowing.

Diagram 9: Flow of electrons



If the electrons constantly move in one direction then one speaks of direct current. The following two symbols are used to indicate direct current on e.g. electric devices and instruments: [ - ] or [ DC ].

Diagram 10: I-t-Diagram for direct current




A current is called alternating current when the flow direction of the electrons is constantly changing in regular time intervals (periodically) with a simultaneous change of the current size. The alternating current energy supply companies are supplying to end users over the public electricity supply systems can be represented as a wave line (sinusoidal curve) with a number of 50 oscillations per second (see diagram 11 below). On electric devices and instruments the following two symbols are used to indicate alternating current: [ ~ ] or [ AC ].


 

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