Resistor is a passive two terminal electronic components. It function is to limit or reduce(resist) the flow of current or divide the voltage in a circuit. The unit of the resister is ohm(Ω). The resistance r of any material is proportional to its length and inversely proportional to its area of cross section A.
R=ρl/A Ω
ρ=specific resistance or resistivity of the material.
Contents
Symbol
Resistor Type
 Fixed Resister
 Wire wound resistor
 Carbon film resistor
 Metal film resistor
 Carbon composition resistor
 Carbon resistor
 Film type resistor
 Chip resistor
 Variable Resister
 Rheostat
 Potentiometer
 Trimmer
 Preset
Resistor Color Code
Color

Digit value

Multiplier

Multiplied Out

Tolerance

Black

0

10^{0}

1


Brown

1

10^{1}

10


Red

2

10^{2}

100


Orange

3

10^{3}

1,000


Yellow

4

10^{4}

10000


Green

5

10^{5}

100,000


Blue

6

10^{6}

1,000,000


Violet

7

10^{7}

10,000,000


Gray

8

10^{8}

100,000,000


White

9

10^{9}

1,000,000,000


Gold

±5%


Silver

±10%

Measuring power across a resistor (Ohm’s Power Law)
Series and parallel resistors
Ohms Law
resistors.
LED Current Limiting
LED. If your LED is red, it might have a forward voltage around 1.8V. If you
want to limit the current to 10mA, use a series resistor of about 720Ω.
Kirchhoff’s Law
of resistors.
Resistor networks
Voltage Dividers
Resistive properties of materials
Material

ρ (Ωm) at 20°C

σ (S/m) at 20°C

Temperature coefficient (1/°C) x10^3

Silver

1.59×10^{−8}

6.30×10^{7}

3.8

Copper

1.68×10^{−8}

5.96×10^{7}

3.9

Gold

2.44×10^{−8}

4.10×10^{7}

3.4

Aluminum

2.82×10^{−8}

3.5×10^{7}

3.9

Tungsten

5.60×10^{−8}

1.79×10^{7}

4.5

Zinc

5.90×10^{−8}

1.69×10^{7}

3.7

Nickel

6.99×10^{−8}

1.43×10^{7}

6

Lithium

9.28×10^{−8}

1.08×10^{7}

6

Iron

1.0×10^{−7}

1.00×10^{7}

5

Platinum

1.06×10^{−7}

9.43×10^{6}

3.9

Tin

1.09×10^{−7}

9.17×10^{6}

4.5

Lead

2.2×10^{−7}

4.55×10^{6}

3.9

Manganin

4.82×10^{−7}

2.07×10^{6}

0.002

Constantan

4.9×10^{−7}

2.04×10^{6}

0.008

Mercury

9.8×10^{−7}

1.02×10^{6}

0.9

Nichrome

1.10×10^{−6}

9.09×10^{5}

0.4

Carbon (amorphous)

5×10^{−4} to 8×10^{−4}

1.25 to 2×10^{3}

0.5

Resister Application
 variable resister is used in volume control in
the TV application,  LED Current Limiting
Examples
Example 1
wire of 0.75km long and having a cross sectional area of 0.01cm^{2}.
(take ρ=1.72×10^{8}ohmm).
Example 2
an aluminium wire of 700m long and having a resistance of 0.24ohm (take ρ=2.83×10^{8}ohmm)
Example 3
across the terminals of a V = 12 volt battery, then a current of (V/R)12 / 300 = 0.04 amperes flows
through that resistor.
Example 4 (Ohm’s law equations)
Consider
a 1ohm resistor in a circuit with a voltage drop from 100V till 10V across its
terminals. What is the current through the resistor? The
triangle reminds us that:
Example 5 (Ohm’s law equations)
Consider
a 10ohm resistor in a circuit subject to a current of 2 Ampere and a voltage
of 120V. What is the voltage drop across the resistor? Using
the triangle shows us that:
Answerer
Thus the voltage at the end terminal is 12020
= 100 V.
Example 6 (Ohm’s Power Law)
Answer:
According to the wheel, P=I^2*R= 0.100^2*50=0.5 W. So the minimal power
rating should be at least 0.5W, but recommended is to go high above this value
for extra reliability and lifetime.
Example 7 (Ohm’s Power Law)
What is the current in the circuit?
This is a basic example of Ohm’s law. Voltage and resistance are known,
so we can calculate current with the equation:
I=V/R=6/1.2=5 A.
Example 8 (Ohm’s Power Law)
is connected in a circuit with 8A current. What is the voltage drop over the
heater?
Voltage can be expressed in current and power with the formula:
V=P/I= 1000/8=125 V
Reference Website
Basic Electricity – Resistance and Ohm’s law