ETEC 4824 Analogue Electronics

Resistors and Ohms Law

Learning Outcomes

• At the end of the lesson, students should be able to :

Explain the function of resistors Determine the resistance of a given resistor

via its colour code Determine the total resistance in a series circuitDetermine the total resistance in a parallel

circuit

Learning Outcomes

State Ohm’s LawDetermine the V, I and power in a series

circuitDetermine the V, I and power in a parallel

circuitApply Kirchhoff Law to determine V and I in a

network circuit.

Resistor

Component oppose the flow of electrical current through itself.

i.e. Resistors limit current.

Resistor

Resistor

• Limiting current for enough current to make the LED light up, but not so much to damage the LED

Resistors

• Are used to direct current flow to particular parts of the circuit,

• May be used to determine the voltage gain of an amplifier.

• Resistors are used with capacitors to introduce time delays

Symbol

Fixed Value Resistors

A carbon film resistor

Resistors Colour CodeNumber Colour

0 black1 brown2 red3 orange4 yellow5 green6 blue7 violet8 grey9 white

Resistors Colour Code

Resistors Colour Code

• The first band on a resistor is interpreted as the FIRST DIGIT of the resistor value

• The second band gives the SECOND DIGIT • The third band is called the MULTIPLIER - tells you how many noughts you should write

after the digits you already have

Resistors Colour Code - Tolerance

Tolerance Colour

±1% brown

±2%red

±5% gold

±10% silver

Resistors Colour Code - Tolerance

• The remaining band is called the TOLERANCE band.

• This indicates the percentage accuracy of the resistor value

Questions

• Determine the resistor value from the following colour coded resistors :

• 1. green, blue, red and gold• 2. orange, white, yellow and red• 3. blue, grey, green and brown• 4. brown, black, brown and red• 5. grey, red, black and gold

• kilo (k) = 1,000 = X 103

• mega (M) = 1,000,000 = X 106

• giga (G) = 1,000,000,000 = X 109

• tera (T) = 1,000,000,000,000 = X 1012

• milli (m) = 0.001 = X 10-3

• micro (µ) = 0.000001 = X 10-6

• nano (n) = 0.000000001 = X 10-9

• pico (p) = 0.000000000001 = X 10-12

Ohm's law

• the current through a conductor between two points is directly proportional to the potential difference across the two points.

• the usual mathematical equation that describes this relationship:[2]

Ohm's law

Ohm's law

• What is the current flow through a 5 Ω resistor if the voltage drop is 10 V.

•

A25

10VI

Ohm's law

• What is the voltage drop across a 10 Ω resistor if current flow through it is 0.5A

• V = 0.5 A x 10 Ω• = 5 V

Ohm's law

• What is the resistance of a load if the voltage drop across is 10V and current flow through it is 0.5A

205.010AVR

Series Circuit

• Resistors are arranged in a chain

• Current has only one path to take.

Series Circuit

Series Circuit

• Total Resistance Rt = R1 + R2

Series Circuit

• Given : R1 = 27Ω,

• R2 = 22 Ω,

• E = 12 V• Calculate : Rt , Is

• V1 and V2

Series Circuit

• Given : R1 = 10Ω,

• R2 = 22 Ω,

• E = 2 V• Calculate : Rt , Is

• V1 and V2

Series Circuit

Series Circuit

• Given : R1 = 10Ω,

• R2 = 22 Ω, R3 = 15 Ω

• E = 2 V• Calculate : Rt , Is

• V1 , V2 and V3

Voltage Divider

ERR

RV

21

11

ERR

RV

21

22

Voltage Divider

• Given : R1 = 27Ω,

• R2 = 22 Ω,

• E = 12 V• Calculate : V1 and V2

Voltage Divider

• Given : R1 = 10Ω,

• R2 = 22 Ω, R3 = 15 Ω

• E = 12 V• Calculate : V1 , V2 and V3

Parallel Circuit

• Two or more components are connected in parallel they have the same potential difference (voltage) across their ends

Parallel Circuit

Parallel Circuit

21

111

RRRT

11

2

1

11

R

E

R

V

R

VI

22

1

2

22

R

E

R

V

R

VI

Parallel Circuit

• Given : R1 = 10Ω,

• R2 = 22 Ω,

• E = 2 V• Calculate : Rt , I1

• I2 and Is

Parallel Circuit

• Given : R1 = 10Ω,

• R2 = 10 Ω,

• E = 2 V• Calculate : Rt , I1

• I2 and Is

Parallel Circuit

• Given : R1 = 10Ω,

• R2 = 100 Ω,

• E = 6 V• Calculate : Rt , I1

• I2 and Is

Parallel Circuit

• Given : R1 = 10Ω,

• R2 = 100 Ω,

• R3 = 10 Ω,• E = 6 V• Calculate : Rt , I1

• I2 , I3 and Is

Power

• is the rate at which energy is transferred, used, or transformed.

• Unit : Watt (W)• P = V x I• P = V2 /R• P = I2 x R

Power

• Given : I = 200 mA , R = 6 Ω• Calculate power dissipated in R

• P = I2 x R• = (200x10-3)2 x 6• = 240 mW

Power

• Given : R = 5Ω , V = 6V• Calculate power dissipated in R

• P = V2 / R• = 62 / 5• = 7.2 W

Power

• Given : R = 5Ω , I = 1.2A• Calculate power dissipated in R

• P = I2 x R• = 1.22 x 5• = 7.2 W

Power

• Given : R1 = 10 Ω, R2 = 5 Ω

• E = 6 V• Calculate power dissipated in R1 and R2

Power

• Given : R1 = 10 Ω, R2 = 5 Ω

• Is = 400 mA

• Calculate power dissipated in R1 and R2

Power

• Given : R1 = 10Ω,

• R2 = 100 Ω,

• R3 = 10 Ω,

• E = 6 V• Calculate : power dissipated in R2

Kirchhoff's voltage law (KVL)

• The directed sum of the electrical potential differences (voltage) around any closed circuit is zero, or:

• The algebraic sum of the products of the resistances of the conductors and the currents in them in a closed loop is equal to the total emf available in that loop.

Kirchhoff's voltage law (KVL)

• v1 + v2 + v3 - v4 = 0 or• v1 + v2 + v3 = v4

Kirchhoff's current law (KCL)

• At any node (junction) in an electrical circuit, the sum of currents flowing into that node is equal to the sum of currents flowing out of that node, or:

• The algebraic sum of currents in a network of conductors meeting at a point is zero.

Kirchhoff's current law (KCL)

• i1 + i4 = i2 + i3

• http://www.opamp-electronics.com/tutorials/dc_theory.htm