etec 4824 analogue electronics resistors and ohms law
Post on 26-Dec-2015
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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
• 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
Resistors Colour CodeNumber Colour
0 black1 brown2 red3 orange4 yellow5 green6 blue7 violet8 grey9 white
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
• 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
• Given : R1 = 10Ω,
• R2 = 22 Ω, R3 = 15 Ω
• E = 2 V• Calculate : Rt , Is
• 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
• 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 , I = 1.2A• Calculate power dissipated in R
• P = I2 x R• = 1.22 x 5• = 7.2 W
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 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.
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