# Advice 1: How to determine the resistance of the resistor

To determine the resistance of the resistor, it is easier and safer to just measure it with an ohmmeter or multimeter. However, this method is not always available, starting with the basic lack of the necessary instrument, to physical inaccessibility of a part. In addition, before measurement of resistance of the resistor must desoldering from the circuit, but it is not always possible. In this case, will the determination of the resistance of the resistor by its markings.
You will need
• resistor, an ohmmeter, a multimeter, a magnifying glass.
Instruction
1
The easiest way to determine the resistance of the resistor is to learn about it from the relevant documentation. If the resistor is purchased as a standalone item, find the supporting documents (invoice, warranty card, etc.). Find in them the value of the resistor. Most likely, the resistance value will be specified next to the part name, for example, a resistor of 4.7 K. In this case, the number means the value of the resistor, and the letter (s) is a unit of measurement. Options K, K, Kom, kom, Kom, kom correspond to kiloohm.The same designation with the letter "M" instead of "to" - megohms. If the letter "m" will be lowercase (small), theoretically this corresponds to a milliohm. However, in practice, such resistors are not normally sold, but are made independently from several coils of special wire. Therefore, combinations with the letter "m" can be attributed to the megohms (in unusual cases, it is better to specify).The lack of after the number of units or the presence of the word "Om" or "om" means, respectively, in Ohms. (in practice, may mean that the seller simply does not have the unit).
2
If the resistor is part of an electric (electronic) devices take the electrical diagram of this device. If no schematic, try to find it on the Internet. Look at the diagram of the corresponding resistor. Resistors are indicated by small rectangles with lines emerging from the short sides. Inside the rectangle can be dashes (represent power). To the designation of the resistor (rectangle) is usually the letter R and a numeral indicating the ordinal number of the resistor in the circuit, for example, R10. After the designation of the resistor indicate its value (slightly to the right or below). If the resistance of the resistor is not specified, the view in the lower part of the diagram – sometimes resistor values (grouped by values) are in there.
3
If you have a ohmmeter or multimeter, just connect the device to the conclusions of the resistor and record the readings. Pre-multimeter switch to the measurement mode of resistance. If the ohmmeter "rolls" or on the contrary, shows a very small value, set it to any range. If the resistor is part of the scheme, the pre-wipaire it, otherwise the readings will probably be incorrect (smaller).
4
The value of the resistor can also be identified by its marking. If the denomination consists of two digits and one letter (typically for the old "Soviet" parts), then use the following rule:
The letter is put in place and the decimal point represents a multiple of the prefix:K – kilo Ohm;
M – Megohm;
E – units, i.e. in this case Om.If the value of the resistor is an integer, then the corresponding letter is used at the end of the designation (69К = 69 kOhm). If the resistance of the resistor is less than one letter is placed before the number (M15 = 0.15 Mω = 150 kω). In fractional denominations of the letter is between numbers (9Е5 = 9.5 Ohm).
5
Numbers consisting of three digits, remember the following simple rule: the first two digits need to add as many zeros as indicated by the third digit. For example, 162, 690, 166 interpreted as follows:162 = 16’00 Ohms = 1.6 kω;
690 = 69’ Om = 69 Ohms;
166 = 16’000000 Ohm = 16 MOhm.
6
If the value of the resistor is marked with colored stripes, turn it off (or turn) to the individual (apart from three) strip was to the right. Then, using the following table, match colors, put the color stripes in the numbers are: black - 0;
brown - 1;
red - 2;
- orange - 3;
- yellow - 4;
green - 5;
blue - 6;
purple - 7;
gray - 8;
- white - 9.After receiving a three-digit number, use the rule described in the preceding paragraph. So for example, if the color of the three stripes in the following order, i.e. from left to right (red - 2, orange - 3, yellow - 4), we obtain the number 234, which corresponds to the nominal value of 230000 Ohms = 230 kω. By the way, the above table is very easy to remember. Order medium colors corresponding to the rainbow, and extreme color to the end of the list become lighter.

# Advice 2 : How to determine the power resistor

To determine the power resistor , take a voltmeter and connect in parallel to the resistor in the circuit. Then turn on the ammeter in the circuit. Take readings of current and voltage and multiply their values, the result is a power current to the resistor. It is possible to measure the power of the resistorand knowing the resistance and one of the values of the current or voltage or by using a special device – power meter.
You will need
• A current source, ammeter, voltmeter, ohmmeter and wattmeter.
Instruction
1
Determination of the power resistor with a voltmeter and ammeter Assemble an electrical circuit, which enable the resistor and the ammeter. To the terminals of the resistor connect the voltmeter. When connected to a DC power source observe the rules of connection devices (the positive pole of the device always connect to the positive pole of the current source). After connecting the circuit to the current source, remove the current reading is in amperes (ammeter) and voltage in volts (voltmeter). The resulting values multiply (P=UI), and the result is a power resistor in watts.
2
Determination of the power resistor with a voltmeter If the resistance of the resistor is known (it is specified directly on the case or measure it with an ohmmeter), connect it to the terminals of the voltmeter. The assembled circuit connect to power source. Measure the voltage across the resistor in volts. Next, take the value of the voltage in the square, and divide by the resistance (P=U2/R and power resistor.
3
Determination of the power resistor the ammeter When the known impedance circuit to the power supply, including successively ammeter. Measure the amperage in the circuit by the ammeter in amperes. Next, take the value of the current in the square and multiply by the resistance value of the resistor (P=I2R).
4
Determination of the power resistor the power meter Assemble the circuit consisting of a resistorand parallel connected to the power meter. Connecting it to a power source, see power resistor on the scale or screen of the device. Units, in this case, adjust within the permitted device. It can be watts, milliwatts, kilowatts, etc.
Note
In all cases, in order to collect safety circuit is disabled when the current source.

# Advice 3 : How to calculate voltage drop

The drop in the voltage across the load can be calculated if you know at least any two of the following three values: the capacity allocated at the load, current through it and its resistance. If you know more than two values, the conditions of the problem are redundant.
Instruction
1
If the calculations have not be implemented for this task from a textbook, and in the parameters of a real experiment, to measure voltage , connect the voltmeter in parallel with the load to measure current - ammeter in series with the load for measuring resistance - the ohmmeter in parallel, the load is de-energized, and to measure emitted power, put the load inside the calorimeter. In all cases, use caution. In this case, it is assumed that the measurement voltage at the load for one reason or another impossible, therefore we have to measure other parameters (the combination of resistance and current, the combination of resistance and capacity or a combination of current and power), then use in calculations.
2
Be sure to translate all quantities to SI before performing calculation. It is much easier, than then to be transferred to the system result.
3
In case you do not know the current through the load and the resistance, to calculate the drop of voltage it can use Ohm's law: U=RI where U is the desired drop in voltage on load (In); R - load resistance (Ohms); I is the electric current passing through the load.
4
If you know the load resistance, and allocated to her power, output the formula for calculating voltage on it in the following way: P=UI, U=RI. Therefore, I=U/R, P=(U^2)/R. this implies that U^2=PR, U=sqrt(PR) where U is the desired drop in voltage on load (V); P is the power produced at the load (W); R - load resistance (Ohms).
5
If you know the current through the load and allocated to it the power use when calculating the falling voltage at the load by the following considerations: P=UI. Therefore, U=P/I, where U is the desired drop in voltage on load (V); P is the power produced at the load (W); I is the electric current passing through the load.
6
If you have multiple series-connected loads, and the known ratio of their resistances or allocated to capacity take note of the fact that the current through each of them the same and equal to the force of the current in the entire circuit.

# Advice 4 : How to find the value of the resistor

Designation of the values of resistors on the schematics and the components are performed according to different standards. In addition, some resistors for the encoding numbers are used instead of numbers, the color of the ring.
Instruction
1
On the wiring diagram the resistor are given without specifying the unit of measurement is generally expressed in ohms. For example, the number 200 means 200 Ohms. If after the numbers located lowercase letter K, we are talking about Kromah: 250 to 250 is file com. If the old schemes unit of measurement in the designation is absent, and the number in addition to a part is and the fractional, the value is expressed in megohms: 10,0 stands for 10 MW. On new schemes to do this, use the capital letter M: 5 M means 5 Mω. Capital letter G replaces the unit dimension D (gigaom). These resistors are rare, mainly in radiation equipment based on ionization chambers.
2
On the resistors instead of using the name Om unit uses either the Latin capital letter R or a capital Greek letter Ω (omega"). Kilome are denoted by the capital letter K, megohms - capital letter M, higami - uppercase Russian letter G Latin or G. the Numbers located before and after the letters is the equivalent of digits after the decimal point. For example, 2R5 - 2.5 Ohm, 120K - 120 ohms, 4М7 - 4.7 Mω. Less the resistance value is specified using the conventional notation of units, for example, 10 kω.
3
Using the color rings on the resistors are coded with different numbers. The following colors are used: black - 0, brown - 1, red - 2, orange - 3, yellow - 4, green - 5, blue - 6, violet - 7, grey - 8, white - 9. These bands may be three or four. All of them, except the last, represent numbers, and the last is number of zeros following those digits. The resulting number expresses the resistance in ohms, which can be converted to more convenient units.
4
If after them after a short period of located gold band, the resistor has a tolerance of 5%. The silver band tells about the tolerance of 10%, and if it does not exist, the tolerance on resistance equal to 20%. Countdown guide strips on the side opposite the strip, symbolizing tolerance.
5
The resistor on which the marking is absent, the resistance can be measured. To do this, power off the circuit, discharge the capacitors, confirm with a voltmeter that they are really discharged, and then desolder one lead of the resistor and connect it to an ohmmeter. Select the limit at which resistance is displayed most accurately. After reading the readings, disconnect the ohmmeter and solder the disconnected output back.
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