Capacitor

Capacitor

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Capacitor is an electronic component that stores electric charge. The capacitor is made of 2 close conductors (usually plates) that are separated by a dielectric material. The plates accumulate electric charge when connected to power source. One plate accumulates positive charge and the other plate accumulates negative charge.

The capacitance is the amount of electric charge that is stored in the capacitor at voltage of 1 Volt.

The capacitance is measured in units of Farad (F).

The capacitor disconnects current in direct current (DC) circuits and short circuit in alternating current (AC) circuits.

Capacitance

The capacitance (C) of the capacitor is equal to the electric charge (Q) divided by the voltage (V):

C is the capacitance in farad (F)

Q is the electric charge  in coulombs (C), that is stored on the capacitor

V is the voltage between the capacitor's plates in volts (V)

Capacitance of plates capacitor

The capacitance (C) of the plates capacitor is equal to the permittivity (ε) times the plate area (A) divided by the gap or distance between the plates (d):

 

C is the capacitance of the capacitor, in farad (F).

ε is the permittivity of the capacitor's dialectic material, in farad per meter (F/m).

A is the area of the capacitor's plate in square meters (m²].

d is the distance between the capacitor's plates, in meters (m).

Capacitors in series

  

The total capacitance of capacitors in series, C1,C2,C3,.. :

Capacitors in parallel

The total capacitance of capacitors in parallel, C1,C2,C3,.. :

C_Total = C₁+C₂+C₃+...

Capacitor's current

The capacitor's momentary current i_c(t) is equal to the capacitance of the capacitor,

times the derivative of the momentary capacitor's voltage v_c(t):

Capacitor's voltage

The capacitor's momentary voltage v_c(t) is equal to the initial voltage of the capacitor,

plus 1/C times the integral of the momentary capacitor's current i_c(t) over time t:

Energy of capacitor

The capacitor's stored energy E_C in joules (J) is equal to the capacitance C in farad (F)

times the square capacitor's voltage V_C in volts (V) divided by 2:

E_C = C × V_C ² / 2

AC circuits

Angular frequency

ω = 2π f

ω - angular velocity measured in radians per second (rad/s)

f  - frequency measured in hertz (Hz).

Capacitor's reactance

Capacitor's impedance

Cartesian form:

Polar form:

Z_C = X_C∟-90º

Capacitor types

Variable capacitor	Variable capacitor has changeable capacitance
Electrolytic capacitor	Electrolytic capacitors are used when high capacitance is needed. Most of the electrolytic capacitors are polarized
Spherical capacitor	Spherical capacitor has a sphere shape
Power capacitor	Power capacitors are used in high voltage power systems.
Ceramic capacitor	Ceramic capacitor has ceramic dielectric material. Has high voltage functionality.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

RESISTORS

RESISTORS

Resistors determine the flow of current in an electrical circuit. Where there is high resistance in a circuit the flow of current is small, where the resistance is low the flow of current is large. Resistance, voltage and current are connected in an electrical circuit by Ohm’s Law.

When a resistor is introduced to a circuit the flow of current is reduced. The higher the value of the resistor the smaller/lower the flow of current.

Resistors are used for regulating current and they resist the current flow and the extent to which they do this is measured in ohms (Ω). Resistors are found in almost every electronic circuit.

The most common type of resistor consists of a small ceramic (clay) tube covered partially by a conducting carbon film. The composition of the carbon determines how much current can pass through.

           

Resistors are too small to have numbers printed on them and so they are marked with a number of coloured bands. Each colour stands for a number. Three colour bands shows the resistors value in ohms and the fourth shows tolerance. Resistors can never be made to a precise value and the tolerance band (the fourth band) tells us, using a percentage, how close the resistor is to its coded value. The resistor on the left is 4700 ohms.

COLOR	DIGIT	MULTIPLIER	TOLERANCE	TC
Silver		x 0.01 W	±10%
Gold		x 0.1 W	±5%
Black	0	x 1 W
Brown	1	x 10 W	±1%	±100*10-6/K
Red	2	x 100 W	±2%	±50*10-6/K
Orange	3	x 1 kW		±15*10-6/K
Yellow	4	x 10 kW		±25*10-6/K
Green	5	x 100 kW	±0.5%
Blue	6	x 1 MW	±0.25%	±10*10-6/K
Violet	7	x 10 MW	±0.1%	±5*10-6/K
Grey	8	x 100 MW
White	9	x 1 GW		±1*10-6/K