Resistors

Colour Code

SI Units

Resistors

• Used to limit amount of current in circuit

• There must always be some resistance in a circuit.

• Three properties of resistors:– resistance value– tolerance– power rating

Resistors

• Resistance and tolerance value determined by coloured bands on resistor

• Power rating determined by size or composition of resistor

• Schematic symbols:

Box Symbol

Z igzag Symbol

Resistor Types

• Fixed value

• Variable

– Rheostat - two terminals, one fixed, one sliding– Potentiometer - three terminals, two fixed, one

sliding

Colour Band 11st Digit

Band 22nd Digit

Band 3Multiplier

Band 4Tolerance

Black 0 0 x 1 -Brown 1 1 x 10 1%Red 2 2 x 100 2%Orange 3 3 x 1,000 -Yellow 4 4 x 10,000 -Green 5 5 x 100,000 0.5%Blue 6 6 x 1,000,000 0.25%Violet 7 7 x 10,000,000 0.1%Grey 8 8 - -White 9 9 - -Gold - - x 0.1 5%Silver - - x 0.01 10%No band - - - 20%

Colour Codes

Colour Codes

1st D ig it 2nd D ig it M ultip lier Tolerance

Value = ?

Scientific Notation

Prefix Symbol Factor

Tera T x 1012

Giga G x 109

Mega M x 106

Kilo k x 103

Milli m x 10-3

Micro x 10-6

Nano n x 10-9

Pico p x 10-12

SI Units:• IEEE adopted the International System of Units in 1965

proposed in France 1960 (Systeme International d’Unites)

Quantity SI Base Unit Unit Symbol

length/distance meter m

mass gram g

time second sec

electric current ampere A

elec potential diff. volt V

elec resistance ohm elec power watt W

SI Unit Prefixes:Prefix Factor by which the base unit is Multiplied Letter Symbol

exa 1 000 000 000 000 000 000 = 1018 E

peta 1 000 000 000 000 000 = 1015 P

tera 1 000 000 000 000 = 1012 T

giga 1 000 000 000 = 109 G

mega 1 000 000 = 106 M

kilo 1 000 = 103 k

hecto 1 00 = 102 h

deka 1 0 = 101 da

Base Unit 1

deci 0.1 = 10-1 d

centi 0.01 = 10-2 c

milli 0.001 = 10-3 m

micro 0.000 001 = 10-6 nano 0.000 000 001 = 10-9 n

pico 0.000 000 000 001 = 10-12 p

femto 0.000 000 000 000 001 = 10-15 f

atto 0.000 000 000 000 000 001 = 10-18 a

bits and Bytes • bit - short for binary digit. In binary system a bit

can be either 0 or 1.

• Byte - In order to represent numbers, letters, and special characters, bits are combined into groups of eight bits called bytes. Each byte typically represents one character - in many computers, one addressable storage location. The capacity of main memory is expressed in numbers of bytes.

commonly used unitsThere are four commonly used units of measurement to describe

memory capacity:• kilobyte - abbreviated k, kB, or k-byte - is equivalent to

approximately 1000 bytes.

(More precisely, 1kB = 1024 bytes = 210 bytes. The older IBM PCs had a top capacity of 640KB, or about 640,000 characters of data.

• megabyte - MB or M-byte - represents about 1 million (106) bytes. Precisely 1 kB x 1 kB = 1024 x 1024 = 210 x 210 = 220 = 1048576 bytes.

• gegabyte - GB or G-byte - represents about 1 billion (109) bytes. Precisely 1 kB x 1 kB x 1 kB = 1024 x 1024 x 1024 = 210 x 210 x 210 = 230 = 1073741824 bytes.

• terebyte - TB or T-byte - represents 1 about trillion (1012) bytes. Precisely 1 kB x 1 kB x 1 kB x 1 kB = 1024 x 1024 x 1024 x 1024 = 210 x 210 x 210 x 210 = 240 = 1099511627776 bytes.