Basic Electrical Theory

This article I go over to the layman who wants to know and learn electrical engineering or for those already engaged in electrical engineering just to recall the basic theories of electricity.

1. Electric current

is a continuous flow of electrons and continuous on the conductor due to differences in the number of electrons in some locations the number of electrons is not the same. unit of electric current is Ampere.
Electric current moves from the positive terminal () to the negative terminal (-), while the flow of electricity in metal wire consists of moving electrons flow from negative terminal (-) to the positive terminal (), direction of electric current is considered contrary to the direction of movement of electrons.

Figure 1. The direction of electric current and the direction of electron movement.

"1 ampere is the flow of electrons flow as much as 624x10 ^ 16 (6.24151 × 10 ^ 18) or equal to 1 Coulumb per second through a conductor cross-section"

Electric current formula is:

I = Q / t (ampere)

I = magnitude of electric current flow, amperes
Q = amount of electric charge, coulomb
t = time, seconds

2. Electric Current

Is the current which depends on the extent of free electrons that move through a wire cross section in unit time.

Definition: "Ampere is the unit of electric currents that can separate 1.118 milligrams of pure silver from silver nitrate in one second."

The formula - a formula to calculate the number of electric charges, currents and times:

Q = I x t
I = Q / t
t = Q / I

Q = Number of electric charge in units of coulomb
I = Current in units of Ampere.
t = time in seconds.

"Strong electrical currents also called electric current"

"Electrical charge has a positive charge and negative charge.Positive charge carried by protons, and negative charge carried by electro. Cargo unit "coulomb (C)", the charge of protons 1.6 x 10 ^-19c, while the electron charge -1.6 x 10 ^-19c. Marked the same charge repel each other, marked with different charges attract each other "

3. Current Density

"Current density is the amount of electric current for each mm ² wire cross-sectional area."

An electric current flowing in the wire evenly according Conductor cross section. 12 A flow of electric current in the wire, incorporating 4mm ², then the current density 3A/mm ² (12A / 4 mm ²), when the cross-section 1.5 mm ² Conductor shrink, then the current density becomes 8A/mm ² (12A / 1.5 mm ²).

Current density effect on temperature rise. Conductor temperature is maintained around 300 ° C, where the ability of cable flow conductivity is defined in tables Ability Flow Conductivity (CRC).

Based on cable CRC table in the table above, incorporating the cable 4 mm ², 2 core cable has a CRC 30A, has a current density 8.5 A / mm ². Current density is inversely proportional to the cross-section Conductor, Conductor cross-section the greater the current density decreases.

The following formulas to calculate the amount of current density, currents and cross-wire:

J = I / A
I = J x A
A = I / J

Meeting current J = [A / mm ²]
I = Currents [Amp]
A = wire cross-sectional area [mm ²]

4. Resistivity and Conductivity Conductor

Conductor of metal material easy flow of electric current, copper and aluminum has a high electrical conductivity. Materials consist of a collection of atoms, each atom consists of protons and electrons. The flow of electric current is the flow of electrons. The free electrons flow is challenged as it passes through the atom next to it. The result is friction and this causes electrons denganatom of heat. Conductor Resistivity inhibiting properties that occurred in each material.

Prisoners are defined as follows:

"1 Ω (one Ohm) is the resistance of the mercury column whose length is 1063 mm with cross section 1 mm ² at a temperature of 0 ° C"

Conductivity is defined as follows:

"The ability Conductor conductivity or current flow while the insulation or the insulation is a material that has a huge resistance so it does not have the power hantarnya conductivity or small, which means very difficult electrified."

The formula for calculating the electrical resistance of the conductivity currents:

R = 1 / G
G = 1 / R

R = resistance / resistance [Ω / ohm]
G = conductivity Power flow / conductivity [Y / mho]

Conductor Resistivity magnitude is inversely proportional to cross section and also the resistance of conductors according to Ohm's law.

"When a Conductor with a length l, and q-sectional diameter and resistivity ρ (rho), then the detainee Conductor is":

R = ρ x l / q

R = wire resistance [Ω / ohm]
l = length of the wire [m / m] l
ρ = resistivity of wire [Ωmm ² / m]
q = wire cross section [mm ²]

faktot-resistant factors that affect the value or detention, as prisoners of a type of material is highly dependent on:
• Conductor length.
• conductor cross-sectional area.
• type of conductor.
• temperature.

"Prisoners Conductor influenced by temperature, when temperature increases the atomic bonding is increasing as a result of electron flow is hampered. As such rise in temperature causes the increase in prisoners Conductor"

5. potential or voltage

electric potential is the phenomenon of migration of electrical potential due to a different location. of this, we know the difference in electrical potential which is often called "potential difference or potential difference." unit of potential difference is the Volt.

"The Volt is the potential difference between two points when one joule of effort to move the electric charge of one coulomb"

Formulation of a potential difference or voltage is:

V = W / Q [V]

V = potential difference or voltage, in volts
W = business, in newton-meters or Nm or joule
Q = electric charge, the coulomb


In an electrical circuit current will flow, if fulfilled the requirements as follows:
1. The existence of voltage source
2. The existence of interface
3. Because the burden of

Figure 4. Electrical circuit.

At the switch S is open then the current will not flow through the load. When switch S is closed then current will flow to the load R and Ampere meter will appoint. In other words, current flow conditions in a circuit must be closed.

1. How to Measure Installation Tool.
Installation of measuring devices mounted volt meter in parallel with the source voltage or load, because the prisoners in the volt meter is very high. Conversely installation Ampere meter gauge mounted series, it inidisebabkan prisoners in the Ampere-meter is very small. [Image] Add caption
"Voltage measuring instrument is a voltmeter and measure electric current is ammeters"

2. Ohm's Law
In a closed circuit, I changed the flow magnitude is proportional to the voltage V and inversely proportional to the load resistance R, or otherwise with the formula: [Image] Add caption
I = V / R
V = R x I
R = V / I

I = electric current, amperes
V = voltage, volts
R = resistance or resistance, ohm

• Formula for counting Power (P), in units of watts is:
P = I x V
P = I x I x R
P = I ² x R

3. LEGAL Kirchoff

At each electrical circuit, the algebraic sum of currents which meet at one point is zero (ΣI = 0).

[Image] Add caption

Figure 5. loop currents "Kirchoff"

I1 (-I2) (-I3) I4 (-i5) = 0
I1 = I2 I3 I4 I5