Fundamental Physics/Electronics/Resistors
Contents
Resistor[edit]
A resistor ( ) is an electronic component that resists, restricts, or opposes the flow of electrical current.
Symbol[edit]
Resistor Construction[edit]
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:
where is the length of the conductor, measured in metres [m], A is the crosssection 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 ohmmetres (Ω·m).
In This formula are constant,therefore already is constant.
Resistor's Resistance[edit]
Resistance is the resistor's characteristic to resist the current flow and reduces the voltage. Resistance has symbol R measured in ohm Ω can be calculated from Ohm's law
Ohm's law
Therefore,
Resistor in DC circuit[edit]
Resistance[edit]
Ohm law
where:
 R is resistance (ohms, Ω),
 V is voltage (volts, V),
 I is current (amperes, A).
Conductance[edit]
Conductance (G) is defined as the inverse of resistance, calculated as:
where:
 G is conductance (siemens, S).
Voltage[edit]
Voltage is calculated as:
Current[edit]
Current is calculated as:
Power[edit]
Power is calculated as:
Resistor in AC circuit[edit]
Voltage[edit]
Current[edit]
Power[edit]
Reactance[edit]
Impedance[edit]
Phase[edit]
v and i are in phase
Resistor Configuration[edit]
Resistors in Series[edit]
For n resitors connected adjacent to each other as shown
The total resistance
For 2 series resistor of same value
Resistors in parallel[edit]
For n resitors connected facing each other as shown
The total resistance
For 2 parallel resistor of same value
Resistors in 2 port network[edit]
2 resistor to form 2 port network as shown
3 resistor connected in T configuration
3 resistor connected in Π configuration
Resistor color code[edit]
Color  Significant figures 
Multiplier  Tolerance  Temp. Coefficient (ppm/K)  

Black  0  ×10^{0}  –  250  U  
Brown  1  ×10^{1}  ±1%  F  100  S  
Red  2  ×10^{2}  ±2%  G  50  R  
Orange  3  ×10^{3}  –  15  P  
Yellow  4  ×10^{4}  (±5%)  –  25  Q  
Green  5  ×10^{5}  ±0.5%  D  20  Z  
Blue  6  ×10^{6}  ±0.25%  C  10  Z  
Violet  7  ×10^{7}  ±0.1%  B  5  M  
Gray  8  ×10^{8}  ±0.05% (±10%)  A  1  K  
White  9  ×10^{9}  –  –  
Gold  –  ×10^{1}  ±5%  J  –  
Silver  –  ×10^{2}  ±10%  K  –  
None  –  –  ±20%  M  –  

Resistors found in electronic kits and hobby projects have up to four bars indicating the color code. The first two bars represent the first and second significant digit, the third represents the exponent or decimal multiplier, and the fourth represents the tolerance. The chart to the right shows information about the color coding on resistors.
Further Reading[edit]
 The role of resistors in electrical circuits
 Resistors in Series
 Resistors in Parallel
 Resistor's circuit