Resistors are the most commonly used component in electronics and their purpose is to create specified values of  current and voltage in a circuit. A number of different resistors are shown in the photos. (The resistors are on millimeter paper, with 1cm spacing to give some idea of the dimensions). The left photo shows some low-power resistors, while the right shows some higher-power resistors. Resistors with power dissipation below 5 watt (most commonly used types) are cylindrical in shape, with a wire protruding from each end for connecting to a circuit. Resistors with power dissipation above 5 watt are shown below.

Low Power	High Power

The symbol for a resistor is shown in the following diagram (left: American symbol, right: European symbol.) 

Potentiometers

Potentiometers (also called pots) are variable resistors, used as voltage or current regulators in electronic circuits. By means of construction, they can be divided into 2 groups: coated and coiled. With coated potentiometers, insulator body is coated with a resistive material. There is an elastic, conductive slider moving across the resistive layer, increasing the resistance between slider and one end of pot, while decreasing the resistance between slider and the other end of pot.

Coiled potentiometers are made of conductor wire coiled around insulator body.  There is an elastic, conductive slider moving across the wire, increasing the resistance between slider and one end of pot, while decreasing the resistance between slider and the other end of pot.
Coated pots are much more common variant. With these, resistance can be linear, logarithmic, inverse-logarithmic or other function depending upon the angle or position of the slider. Most common are linear and logarithmic potentiometers, and the most common applications are radio-receivers, audio amplifiers, and similar devices where pots are used for adjusting the volume, tone, balance, etc.
Coiled potentiometers are used in devices which require increased accuracy and constancy of attributes. They feature higher dissipation than coated pots, and are therefore a necessity in high current circuits.
Potentiometer resistance is commonly of E6 series, most frequently used multipliers including 1, 2.2 and 4.7. Standard tolerance values include 30%, 20%, 10% (and 5% for coiled pots).

Ohm's Law

Resistance Calculator black brown red orange yellow green blue violet gray white black brown red orange yellow green blue violet gray white black brown red orange yellow green blue violet gray white gold silver gold silver brown red k M ±5% ±10% ±1% ±2% Wait for colours to download

f representing the frequency in Hz and C representing the capacity in Farads.
For example, 5nF capacitor's reactance at f  = 125kHz equals:

while, at f  = 1.25MHz, it equals:

A capacitor has an infinitely high reactance for direct current, because f =0.

Capacitors are used in circuits for filtering signals of specified frequency. They are common components of electrical filters, oscillator circuits, etc.

The basic characteristic of a capacitor is its capacity -  the higher the capacity is, higher  the amount of electricity a capacitor can accumulate. Capacity is measured in Farads (F). As one Farad represents a fairly high capacity value, microfarad (µF), nanoFarad (nF) and picoFarad (pF) are commonly used. As a reminder, relations between units are (1F= 106µF = 109nF = 1012pF) that is 1µF=1000nF and 1nF=1000pF. It is essential to remember this notation, as the same values may be marked differently in different electrical schemes. For example, 1500pF may be displayed as 1.5nF, 100nF could be displayed as 0.1µF, etc. Bear in mind that the simpler notation system is used, as with resistors. If the markings on the capacitor in the scheme reads 120 (or 120E) capacity equals 120pF, 1n2 stands for 1.2nF, n22 stands for 0.22nF, while .1µ (or .1u) stands for 0.1µF capacity and so forth.

Capacitors come in various shapes and sizes, depending on their capacity, working voltage, insulator type, temperature coefficient and other factors. All capacitors can divided in two groups: those with changeable capacity values and those with fixed capacity values.

Block-Capacitors

Commonly, capacitors are marked by a number representing the capacity value printed on the capacitor. As well as the maximal capacitor working voltage is mandatory, and sometimes tolerance, temperature coefficient and some other values are printed too. If, for example, a capacitor is marked as  5nF/40V, it value is 5nF and its maximal working voltage is 40v. Any other 5nF capacitor with higher maximal working voltage can be used instead, but they are usually larger and more expensive.

Sometimes, capacitors of low values will be marked with colors, similar to the four-ring system used with resistors . The first two colors (A and B) represent the first two digits, third color (C) is the multiplier, fourth color (D) is the tolerance, and the fifth color (E) is the working voltage.

With disk-ceramic capacitors  and tubular capacitors  working voltage is not specified, because these are used in circuits with low or no DC voltage. If a tubular capacitor havs five color rings on it, then the first color represents the temperature coefficient, while the other four specify its capacity value in the previously described way.

COLOR	DIGIT	MULTIPLIER	TOLERANCE	VOLTAGE
Black	0	x 1 pF	±20%
Brown	1	x 10 pF	±1%
Red	2	x 100 pF	±2%	250V
Orange	3	x 1 nF	±2.5%
Yellow	4	x 10 nF		400V
Green	5	x 100 nF	±5%
Blue	6	x 1 µF
Violet	7	x 10 µF
Grey	8	x 100 µF
White	9	x 1000 µF	±10%

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