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A resistor is an electronic component that is designed to limit the flow of electrical current in a circuit. It does this by introducing resistance, which is measured in ohms (Ω), to the circuit. Resistors are made from a variety of materials and come in many different shapes and sizes.

They are used in a wide range of electronic devices, including radios, televisions, computers, and many other devices. In a simple circuit, resistors can be used to control the current flow to different parts of the circuit, such as a light or a motor. They can also be used to adjust the voltage or current levels in a circuit to provide the desired levels for the operation of electronic devices.

Some of the main uses of resistors include:

**Limit operating current**: By adding a resistor in series with a circuit element, the overall circuit current can be limited.**Biasing of transistors**and other active devices: Resistors can be used to set the operating point of transistors and other active devices in a circuit.**Voltage division**: Two or more resistors can be connected in series to create a voltage divider circuit, which can be used to reduce the voltage level of a signal.**Signal attenuation**: A resistor can be placed in series with a signal source to reduce the amplitude of the signal.**Power dissipation**: A resistor can be used as a "dummy load" to dissipate excess power in a circuit.**Current sensing**: A resistor can be used in a circuit to sense current flowing through it by measuring the voltage drop across the resistor.

Resistor tolerance refers to the allowable variation of a resistor's resistance value from its nominal (stated) value. It is typically expressed as a percentage, and is usually one of the specifications given for a resistor.

For example, a resistor with a tolerance of 5% will have a resistance value that is within 5% of its nominal value. This means that if the nominal value of the resistor is 1kΩ, the actual resistance value could be anywhere between 950Ω and 1.05kΩ.

The standard resistor tolerance include 1% , 2%, 5%, 10%, and 20% tolerance, there are also special case like 1% and 0.1% tolerance resistors are also available which are used in precision applications.

Resistor values are typically represented by a series of colored bands on the physical component. To read the value of a resistor, you'll need to know the color code for the bands.

The standard resistor color code has four bands: the first two bands represent the first and second significant digits of the resistance value, the third band represents the multiplier (number of zeros to add to the end of the first two digits), and the fourth band is the tolerance, which represents how accurate the resistance value is.

Here is an example of how to read the value of a 4-band resistor:

- The first band is brown, which represents the first significant digit 1.
- The second band is black, which represents the second significant digit 0.
- The third band is orange, which represents the multiplier x10^3 (or 1000).
- The fourth band is gold, which represents a tolerance of +/-5%.

So the resistance value of this resistor is: (1 x 10^3) + (0 x 10^0) = 1000 ohms or 1k ohm.and the tolerance is of +-5%.

You can also use our resistor value calculator.

Standard resistor value sets refer to the specific resistance values that are most commonly used in electronic circuits. These standard values are based on a preferred number system, which allows for a convenient and efficient selection of resistor values.

The most common standard resistor value series is the EIA (Electronic Industries Alliance) standard, also known as the E series. The E series includes the following values:10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82.

The E series values are derived from a base of 10, with each value being either the previous value multiplied by the factor 1.2 or divided by the factor 1.2. This allows for a wide range of resistor values with a good spread between them.

Another common standard is the IEC (International Electrotechnical Commission) standard, known as the "Preferred Numbers" which is a similar approach to EIA series, but have some different values.

Many circuit designers prefer to use standard resistor values in their designs because they can easily be obtained from electronic component distributors and they are familiar with their properties.

It's also to be noted that most standard resistor series have a tolerance range that also aligns with the standard values, which is usually 1% or 5%.