What is resistor and resistor calculations.

- What is resistor
- Ohm's law
- Resistors in parallel
- Resistors in series
- Dimensions and material affects
- Resistor image
- Resistor symbols
- Resistor color code
- Resistor types

Resistor is an electrical component that reduces the electric current.

The resistor's ability to reduce the current is called resistance and is measured in units of ohms (symbol: Ω).

If we make an analogy to water flow through pipes, the resistor is a thin pipe that reduces the water flow.

The resistor's current *I* in amps (A) is equal to the resistor's voltage *V* in volts (V)

divided by the resistance *R *in ohms (Ω):

The resistor's power consumption *P* in watts (W) is equal to the resistor's current* I *in amps (A)

times the resistor's voltage *V* in volts (V):

*P* = *I* × *V*

The resistor's power consumption *P* in watts (W) is equal to the square value of the resistor's current *I* in amps (A)

times the resistor's resistance *R* in ohms (Ω):

*P* = *I*^{ 2} × *R*

The resistor's power consumption *P* in watts (W) is equal to the square value of the resistor's voltage *V* in volts (V)

divided by the resistor's resistance *R* in ohms (Ω):

*P* = *V*^{ 2 }/ *R*

The total equivalent resistance of resistors in parallel *R _{Total}* is given by:

So when you add resistors in parallel, the total resistance is decreased.

The total equivalent resistance of resistors in series *R _{total
}*is the sum
of the resistance values:

*R _{total}* =

So when you add resistors in series, the total resistance is increased.

The resistance R in ohms (Ω) of a resistor is equal to the resistivity *ρ*
in ohm-meters (Ω∙m) times the resistor's length l in meters (m) divided by the resistor's cross sectional area *A* in square meters (m^{2}):

Resistor (IEEE) | Resistor reduces the current flow. | |

Resistor (IEC) | ||

Potentiometer (IEEE) | Adjustable resistor - has 3 terminals. | |

Potentiometer (IEC) | ||

Variable Resistor / Rheostat (IEEE) | Adjustable resistor - has 2 terminals. | |

Variable Resistor / Rheostat (IEC) | ||

Trimmer Resistor | Presest resistor | |

Thermistor | Thermal resistor - change resistance when temperature changes | |

Photoresistor / Light dependent resistor (LDR) | Changes resistance according to light |

The resistance of the resistor and its tolerance are marked on the resistor with color code bands that denotes the resistance value.

There are 3 types of color codes:

- 4 bands: digit, digit , multiplier, tolerance.
- 5 bands: digit, digit, digit , multiplier, tolerance.
- 6 bands: digit, digit, digit , multiplier, tolerance, temperature coefficient.

*R* = (10×*digit*_{1 }+* digit*_{2}) ×* multiplier*

*R* = (100×*digit*_{1 }+ 10×*digit*_{2}+*digit*_{3}) ×* multiplier*

Variable resistor | Variable resistor has an adjustable resistance (2 terminals) |

Potentiometer | Potentiometer has an adjustable resistance (3 terminals) |

Photo-resistor | Reduces resistance when exposed to light |

Power resistor | Power resistor is used for high power circuits and has large dimensions. |

Surface mount (SMT/SMD) resistor |
SMT/SMD resistors have small dimensions. The resistors are surface mounted on the printed circuit board (PCB), this method is fast and requires small board area. |

Resistor network | Resistor network is a chip that contains several resistors with similar or different values. |

Carbon resistor | |

Chip resistor | |

Metal-oxide resistor | |

Ceramic resistor |

In digital circuits, pull-up resistor is a regular resistor that is connected to the high voltage supply (e.g +5V or +12V) and sets the input or output level of a device to '1'.

The pull-up resistor set the level to '1' when the input / output is disconnected. When the input / output is connected, the level is determined by the device and overrides the pull-up resistor.

In digital circuits, pull-down resistor is a regular resistor that is connected to the ground (0V) and sets the input or output level of a device to ' 0 '.

The pull-down resistor set the level to ' 0 ' when the input / output is disconnected. When the input / output is connected, the level is determined by the device and overrides the pull-down resistor.

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