# Electronics/Resistors

 Subject classification: this is a science resource.
 Educational level: this is a secondary education resource.
 Type classification: this is a lesson resource.
 Completion status: this resource is ~75% complete.
This is a lesson in the course Electronics, which is a part of the School:Electronics

A resistor ( ${\displaystyle R}$ ) is an electronic component that resists, restricts, or opposes the flow of electricalcurrent.

It can be visualized as constriction or narrowing in a pipe, where the constricted area is the resistance (resistor), and the flow of water is current. The volume of water flow following a constriction in a water pipe is reduced.The resistive property of this type of component can be attributed to a material which has much lower electrical conductivity than regular conductive materials such as metals.

The electrical resistance of a given object depends primarily on two factors:

• What material is it made?
• what is shape?

therefore, can be computed as:

${\displaystyle R=\rho {\frac {l}{A}}}$

where ${\displaystyle l}$ is the length of the conductor, measured in metres [m], A is the cross-section area of the conductor measured in square metres [m²] and ρ (rho) is the electrical resistivity (also called specific electrical resistance) of the material, measured in ohm-metres (Ω·m).

In This formula ${\displaystyle \rho ,{l},{A}}$ are constant,therefore ${\displaystyle R}$ already is constant.

The inverse resistance ${\displaystyle R}$ is conductance ${\displaystyle G}$, the ease at which an electric current passes.therefore, can be computed as:

${\displaystyle G={\frac {1}{R}}={\frac {1}{\rho }}\cdot {\frac {A}{l}}}$

${\displaystyle {\frac {1}{\rho }}=\sigma }$${\displaystyle \sigma }$([[Sigma (sigma) is the electrical conductivity measured in siemens per meter(S·m−1)

${\displaystyle G={\frac {1}{R}}=\sigma \cdot {\frac {A}{l}}}$

In This formula ${\displaystyle \sigma ,{A},{l},}$ are constant,therefore ${\displaystyle G}$ already is constant.

Electrical current ( ${\displaystyle I}$ ) results when a voltage ( ${\displaystyle V}$ ) (or electromagnetic force) causes movement of electrons.

Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points.

${\displaystyle I\propto V}$ then:${\displaystyle V}$ → ↑${\displaystyle I}$ and ↓${\displaystyle V}$ → ↓${\displaystyle I}$

In the electric circuit, if temperature and all other conditions remain constant, R and G are constant therefore relationship between I and V is linearity then:

${\displaystyle I=G\cdot V\;\;\;\;\;\;\;and\;\;\;\;\;\;\;G={\frac {1}{R}}}$
${\displaystyle I={\frac {1}{R}}\cdot V\;\;\;\;\;\;\;or\;\;\;\;\;\;\;I={\frac {V}{R}}}$

R=1,G=1

R>1,G<1

R<1,G>1

Ohm's law can be used to calculate the resistance present in a DC circuit if voltage and current are known.

## Resistance

Every resistor has a resistance calculated as:

${\displaystyle I={\frac {V}{R}}}$${\displaystyle R={\frac {V}{I}}}$

where:

R is resistance (ohms, Ω),
V is voltage (volts, V),
I is current (amperes, A).

## Conductance

Conductance (G) is defined as the inverse of resistance, calculated as:

${\displaystyle G={\frac {1}{R}}}$

where:

G is conductance (siemens, S).

## Voltage

Voltage is calculated as:

${\displaystyle I={\frac {V}{R}}}$${\displaystyle V=I\cdot R}$

## Current

Current is calculated as:

${\displaystyle I={\frac {V}{R}}}$

## Power

Power is calculated as:

${\displaystyle P=I\cdot V\;\;\;\;\;\;\ and\;\;\;\;\;\;\ I={\frac {V}{R}}\;\;\;\;\;\;\ and\;\;\;\;\;\;\ V=R\cdot I}$
${\displaystyle P=I^{2}R\;\;\;\;\;\;\ P={\frac {V^{2}}{R}}}$

## Resistor color code

Color Significant
figures
Multiplier Tolerance Temp. Coefficient (ppm/K)
Black 0 ×100 250 U
Brown 1 ×101 ±1% F 100 S
Red 2 ×102 ±2% G 50 R
Orange 3 ×103 15 P
Yellow 4 ×104 (±5%) 25 Q
Green 5 ×105 ±0.5% D 20 Z
Blue 6 ×106 ±0.25% C 10 Z
Violet 7 ×107 ±0.1% B 5 M
Gray 8 ×108 ±0.05% (±10%) A 1 K
White 9 ×109
Gold ×10-1 ±5% J
Silver ×10-2 ±10% K
None ±20% M
1. Any temperature coefficent not assigned its own letter shall be marked "Z", and the coefficient found in other documentation.