# Electronics/Resistors

This is a lesson in the course Electronics, which is a part of the School:Electronics

A resistor ( $R$ ) 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:

$R=\rho {\frac {l}{A}}$ where $l$ 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 $\rho ,{l},{A}$ are constant,therefore $R$ already is constant.

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

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

$G={\frac {1}{R}}=\sigma \cdot {\frac {A}{l}}$ In This formula $\sigma ,{A},{l},$ are constant,therefore $G$ already is constant.

Electrical current ( $I$ ) results when a voltage ( $V$ ) (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.

$I\propto V$ then:$V$ → ↑$I$ and ↓$V$ → ↓$I$ 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:

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

$I={\frac {V}{R}}$ $R={\frac {V}{I}}$

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:

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

where:

G is conductance (siemens, S).

## Voltage

Voltage is calculated as:

$I={\frac {V}{R}}$ $V=I\cdot R$

## Current

Current is calculated as:

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

## Power

Power is calculated as:

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

## 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.