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 circuit  Determine the total resistance in a parallel circuit

Learning Outcomes  State Ohm’s Law  Determine the V, I and power in a series circuit  Determine the V, I and power in a parallel circuit  Apply 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

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 Code NumberColour 0black 1brown 2red 3orange 4yellow 5green 6blue 7violet 8grey 9white

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 ToleranceColour ±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 10 3 mega (M) = 1,000,000 = X 10 6 giga (G) = 1,000,000,000 = X 10 9 tera (T) = 1,000,000,000,000 = X milli (m) = = X micro (µ) = = X nano (n) = = X pico (p) = = X

Ohm's law the current through a conductor between two points is directly proportional to the potential difference across the two points.currentproportionalpotential difference the usual mathematical equation that describes this relationship: [2] [2]

Ohm's law

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

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

Series Circuit Resistors are arranged in a chain Current has only one path to take.

Series Circuit

Total Resistance R t = R 1 + R 2

Series Circuit Given : R 1 = 27Ω, R 2 = 22 Ω, E = 12 V Calculate : R t, I s V 1 and V 2

Series Circuit Given : R 1 = 10Ω, R 2 = 22 Ω, E = 2 V Calculate : R t, I s V 1 and V 2

Series Circuit

Given : R 1 = 10Ω, R 2 = 22 Ω, R 3 = 15 Ω E = 2 V Calculate : R t, I s V 1, V 2 and V 3

Voltage Divider

Given : R 1 = 27Ω, R 2 = 22 Ω, E = 12 V Calculate : V 1 and V 2

Voltage Divider Given : R 1 = 10Ω, R 2 = 22 Ω, R 3 = 15 Ω E = 12 V Calculate : V 1, V 2 and V 3

Parallel Circuit Two or more components are connected in parallel they have the same potential difference (voltage) across their endsvoltage

Parallel Circuit

Given : R 1 = 10Ω, R 2 = 22 Ω, E = 2 V Calculate : R t, I 1 I 2 and I s

Parallel Circuit Given : R 1 = 10Ω, R 2 = 10 Ω, E = 2 V Calculate : R t, I 1 I 2 and I s

Parallel Circuit Given : R 1 = 10Ω, R 2 = 100 Ω, E = 6 V Calculate : R t, I 1 I 2 and I s

Parallel Circuit Given : R 1 = 10Ω, R 2 = 100 Ω, R3 = 10 Ω, E = 6 V Calculate : R t, I 1 I 2, I 3 and I s

Power is the rate at which energy is transferred, used, or transformed.energy Unit : Watt (W) P = V x I P = V 2 /R P = I 2 x R

Power Given : I = 200 mA, R = 6 Ω Calculate power dissipated in R P = I 2 x R = (200x10 -3 ) 2 x 6 = 240 mW

Power Given : R = 5Ω, V = 6V Calculate power dissipated in R P = V 2 / R = 6 2 / 5 = 7.2 W

Power Given : R = 5Ω, I = 1.2A Calculate power dissipated in R P = I 2 x R = x 5 = 7.2 W

Power Given : R 1 = 10 Ω, R 2 = 5 Ω E = 6 V Calculate power dissipated in R 1 and R 2

Power Given : R 1 = 10 Ω, R 2 = 5 Ω I s = 400 mA Calculate power dissipated in R 1 and R 2

Power Given : R 1 = 10Ω, R 2 = 100 Ω, R 3 = 10 Ω, E = 6 V Calculate : power dissipated in R 2

Kirchhoff's voltage law (KVL) The directed sum of the electrical potential differences (voltage) around any closed circuit is zero, or:potential differences 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. emf

Kirchhoff's voltage law (KVL) v 1 + v 2 + v 3 - v 4 = 0 or v 1 + v 2 + v 3 = v 4

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:electrical circuitcurrents The algebraic sum of currents in a network of conductors meeting at a point is zero.

Kirchhoff's current law (KCL) i 1 + i 4 = i 2 + i 3

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