Basic Resistance

1. The concept of resistance.
Resistance is what? I know a simple way - Resistance is the electrical resistance of a conductor of electricity, if a good electrical conductor resistance small, poor electrical conductor, the greater the resistance, electrical insulators, the resistance is extremely large.
Resistance of wires:
Resistivity of the wire side of rice on the material, length and cross section of the wire. be calculated as follows:

R = ρ.L / S

• In which ρ is the resistivity of the material depends on
• L is the length of the wire
• S is the conductor cross section
• R is in units of Ohm resistor

2. Resistors in electronic devices.

a) Form and sign: In the electronic resistance is an important component, they are made ​​from carbon and metal compounds depending on the mixing ratio that people generate all kinds of resistor values different numbers.

The shape of the resistor in electronics.

The symbol of resistance on the principle diagram.

b) Unit of electrical resistance

• Resistance unit is Ω (Ohm), KΩ, MΩ
• 1KΩ = 1000 Ω
• 1MΩ = 1000 K = 1,000,000 Ω Ω

b) The recorded value of the resistor

• The smaller resistor values ​​are recorded by the stripe by a general convention of the world. (See picture above)
• The resistor is larger than from 2W or more often written directly on the relative values. For example, the capacity of resistance, the resistance of porcelain.

Back export porcelain of great value are recorded directly.

3. How to read resistor values.

International conventions on color

Colour	The value	Colour	The value
Black	0	Green	5
Brown	A	Blue	6
Red	2	Purple	7
Oranges	3	Gray	8
Gold	4	White	9
		Maiden gold	-1
		As silver	-2

Resistance is often denoted by the fourth round color, precision resistor, the color denoted by the fifth round.

* How to read resistor values ​​within 4 colors:

How to read resistor color ring 4

• Round 4 of the ring at the end are always colored like gold or silver, which is within error of the resistance only when we ignore the value read loop.
• Opposite the last round is round No. 1, followed by the round number two, number three
• Round No. 1 and No. 2 is the next tens and units
• Round 3 is a multiple of the number 10.
• Value = (round 1) (round 2) x 10 ^{(3 caps)}
• Can be calculated within the three is the number zero "0" added to
• Sample as the only error in the first round or round number 3, if the round number 3 is the exponent of the number 10 is negative.

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* How to read resistor values ​​5 colored rings (precision resistor)

• Round 5 of the last round, the round recording error, or 5 round color is the color error of many colors, so difficult for us to determine what is diinh final round, but the last round is always a gap a little further.
• For the last round is round No. 1
• Similar values ​​of reading or 4 colors, but here within the next 4 numbers are multiples of the base 10, the next No. 1, No. 2, No. 3, respectively hundreds, tens and units.
• Value = (round 1) (ring 2) (3) x 10 ^{(caps round 4)}
• Can be calculated within the four is the number zero "0" added to

4 - Practice reading resistor values.

The resistance of different colors in the 3rd round

• When the resistance of different colors in the 3rd round, then we see multiple colors within this color often changes from silver to green leaves, the equivalent resistance <1 Ω to every MΩ.

The resistor color ring number 1 and number 2 change.

• In the figure above is the resistance value is often encountered in practice, when the third round color change, the resistance value in increments of 10.

Exercise - You quickly guess value before the answer appears, when all the values ​​that you guess correctly before the results appear in your knowledge that this was okay!

Exercise - Guess the results of electrical resistance values.

5 - The common value resistor.
I can not find a resistor of any value, the manufacturer provided only about 150 kinds of common resistor values, the table below is the color and the resistance value of the common.

The common resistor values.

6 -. Classification resistor.

• Resistance Normal: Resistance usually has a small resistance from 0.125 W to 0.5 W
• Resistance capacity of : As the resistors have a larger capacity of 1W, 2W, 5W, 10W.
• Resistor, heat: The calling of the capacity of the resistor, this resistor ceramic casing, heat when operating them.

The resistance: 2W - 1W - 0.5 W - 0.25 W

Resistor or heating

7 - Power of the resistor.
When you have a resistor in the circuit, the resistor itself an export consumption is calculated by the formula P

P = U. I = U ² / R = I ^2. R

• According to the above formula shows, the consumption of the electrical resistance depends on the current through resistor or voltage dependent resistors on both ends.
• Power consumption of the resistor is completely calculated before you put the resistor in the circuit.
• If you bring a resistor has a nominal production capacity of less than it would consume the resistor will burn.
• Usually a resistor inserted into the circuit has a nominal capacity of> = 2 times the production that it will consume.

Resistance by the public burning of

• The diagram above shows: source Vcc is 12V, the resistor has a value of 120Ω but have different origins, when the switches K1 and K2 is closed, the resistor will consume the produce is

P = U ² / R = (12 x 12) / 120 = 1.2 W

• When K1 is closed, the resistor has a production capacity of greater than consumption, so no fire resistance.
• When K2 is closed, the resistor has a smaller production capacity of consumption, resistance to fire.

8 - Turn back, philosophy apply:
Turn back Resistance is adjustable to change the value, which we have denoted as VR shape as follows:

Variable shape or symbol on the map

Turn back often assembled in the factory for the repair and calibration of the technicians, variable resistor has a structure as shown below.

Structure of the variable resistor

Pressure Philosophy: Philosophy pressure similar but more variable resistor to adjust and often arranged in front of your user control. For example - Philosophy Pressure Volume, Bass philosophical pressure, etc. Treec. , Philosophy means that philosophy apply a voltage from the input section depending on the severity regulation.

Symbols philosophical principles apply in the diagram.

Shape philosophy in philosophy apply pressure Components

9 - resistors connected in series.

Resistor connected in series.

• The resistors are connected in series with a total value equivalent to the resistor elements combined. RTD = R1 + R2 + R3
• Current flowing through the resistor connected in series have equal value and equal to I = I (U1 / R1) = (U2 / R2) = (U3 / R3)
• From the above formula we see that the pressure drop over the resistor connected in series proportional to the return value dient.

10 - resistor in parallel.

Resistors in parallel

• The resistor in parallel with the RTD equivalent value is calculated by formula (1 / RTD) = (1 / R1) + (1 / R2) + (1 / R3)
• If the circuit has only two resistors in parallel, the
  RTD = R1.R2 / (R1 + R2)
• Current flowing through the resistor in parallel inversely proportional to the resistance value.
  I1 = (U / R1), I2 = (U / R2), I3 = (U / R3)
• Voltage across the resistor in parallel with each other always

11 - Crazy or mixed questions

Resistors get mixed.

• Higher rate of resistance to create a more optimal resistors.
• For example, if you need a resistor can be infected 9K two 15K resistors in parallel and then connected in series with resistor 1.5 K.

12 - Application of the resistor
Resistors are ubiquitous in electronic devices such resistors are important components are indispensable, in the circuit, the resistance has the following effects:

• To control the current through the load to match, for example a 9V bulb, but we only have 12V, you can connect to the bulb with a resistor to reduce voltage drop on resistor 3V.

Connect with a resistor bulb.

- As shown above we can calculate the value of the resistor and accordingly as follows: 9V lamp voltage and current consumption of 2W so that I = P / U = (2 / 9) = amperes which is also the current through the resistor.
- Because the source is 12V, 9V bulbs should be 3V drop on R we deduce that the resistance to find the R = U / I = 3 / (2 / 9) = 27 / 2 = 13.5 Ω
- Power consumption of the resistor is: P = UI = 3. (2 / 9) = 6 / 9 W so we have to use resistors with a capacity of P> 6 / 9 W

• Electrical problems become subject to distribution to obtain a desired voltage from a given voltage.

Demand for the pressure distribution voltage U1 discretion.

From above 12V through R1 and R2 for distributed application we take the voltage U1, U1 voltage depends on the value of two resistors R1 and R2.theo formula.

U1 / U = R1 / (R1 + R2) => U1 = U.R1 / (R1 + R2)

Change the value of R1 or R2 will obtain the desired voltage U1.

• Polarization for transistor operation.

Transistor circuit for polarization

• Participate in the RC oscillator circuit

Oscillator circuit using IC 555