what exactly does each part of the circuit do?
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What exactly does each part of the circuit do?. Measures current Circuit control Source of Electrical Supply Circuit protection Measures electrical pressure Circuit load Conductor. What exactly does each part of the circuit do?. Measures current Circuit control - PowerPoint PPT PresentationTRANSCRIPT
What exactly does each part of the circuit do?
Measures current Circuit control Source of Electrical
Supply Circuit protection Measures electrical
pressure Circuit load Conductor
What exactly does each part of the circuit do?
Measures current Circuit control Source of Electrical
Supply Circuit protection Measures electrical
pressure Circuit load Conductor
What exactly does each part of the circuit do?
Measures current Circuit control Source of Electrical
Supply Circuit protection Measures electrical
pressure Circuit load Conductor
What exactly does each part of the circuit do?
Measures current Circuit control Source of Electrical
Supply Circuit protection Measures electrical
pressure Circuit load Conductor
What exactly does each part of the circuit do?
Measures current Circuit control Source of Electrical
Supply Circuit protection Measures electrical
pressure Circuit load Conductor
What exactly does each part of the circuit do?
Measures current Circuit control Source of Electrical
Supply Circuit protection Measures electrical
pressure Circuit load Conductor
What exactly does each part of the circuit do?
Measures current Circuit control Source of Electrical
Supply Circuit protection Measures electrical
pressure Circuit load Conductor
Open Circuit
Closed Circuit
Short Circuit
What is:
How to decode a resistor.
All components of an electrical circuit have resistance (including the conductors).
A resistor is a component that is specifically designed to oppose current flow.
Resistors are generally made from alloys of metal or carbon based compounds
A few are made from semi-conductor type material (like silicon)
What is a resistor?
Linear resistors – wire wound
Linear resistors – carbon compound
The power rating of a resistor is the amount of heat (I2R – in watts) that a resistor can dissipate before the losses are too great or the resistor is destroyed.
For large power ratings resistance wire is used whereas for low (and physically small) power ratings carbon based resistors are used.
Power ratings of res
To make manufacturing cheaper a series of standard values are manufactured.
These vary for the three main tolerance ranges. Tolerance is the degree of accuracy that the
resistor had been manufactured to. For example a 10Ω resistor with a silver
tolerance band has a tolerance of ±10% and can range from 9Ω to 11Ω.
A variable or “tuning” resistor can be placed in a circuit to compensate for the difference.
Tolerance and preferred values of resistance
Temperature sensitive resistors 2 types
Positive temperature coefficient (PTC)
Negative temperature coefficient (NTC)
PTC – resistance increases with an increase of temperature. Made from metallic oxide or silicon.
NTC – resistance decreases with a decrease of temperature. Made from chromium or nickel with small amounts of semi-conductor material.
Non-linear resistors - Thermistors
Resistance varies as the voltage varies
Used for lightning protection where under normal circumstances the do not conduct but when the voltage reaches a certain level the resistance drops.
Uses also include over voltage protection and signal compensation.
Non-linear resistors – Voltage dependant resistors (VDRs)
Resistance varies as the light varies Usually made from cadmium sulphide
mounted on a plate and covered with a vacuum-deposited metallic grid
Non-linear resistors – Light dependant resistors (LDRs)
Resistor (general) Variable resistor
(rheostat) Variable resistor
(potentionometer) Adjustable resistor PTC thermistor NTC thermistor Voltage dependant
resistor Light dependant resistor
Resistor circuit symbols
+ to C
- to C
Black Beer Rots Our Young Guts But Vodka Goes Well
Black is NO color - nothing, zeroBrown, think brow-ONE. Red, think TWO red lips.Orange, think "orange tree" tree rhymes with three.Yellow, think Yell FOUR help.Green, think of a green FIVE dollar billBlue, think "sick (six) and blue"Violet, think "violet clouds in heaven, rhymes with SEVEN.Grey, thing Gray-EIGHT (great)White, think of white wine, rhymes with NINE
Remembering the resistor colour code
Longer conductor =
How does length affect resistance?
Longer conductor = more resistance Shorter conductor =
How does length affect resistance?
Longer conductor = more resistance Shorter conductor = less resistance
How does length affect resistance?
Longer conductor = more resistance Shorter conductor = less resistance
Resistance α Length
How does length affect resistance?
Conductor cross sectional area
Larger conductor =
How does c.s.a. affect resistance?
Larger conductor = less resistance Smaller conductor =
How does c.s.a. affect resistance?
Larger conductor = less resistance Smaller conductor = more resistance
How does c.s.a. affect resistance?
Larger conductor = less resistance Smaller conductor = more resistance
Resistance α 1 c.s.a
How does c.s.a. affect resistance?
The measure of how resistive a material is, is called resistivity.
How does the conductor material affect resistance?
1 m 1 m
1 m
Ω
R = ρ x ℓ A
Where: R = resistance of conductor in ohmsρ = resistivity of conductors in ohm metersℓ = length of conductor in metersA = c.s.a. of conductor in meters2
Sooo…If we put all of them together…..
When current flows through a conductor it heats up
The amount of change in resistance is known as the temperature coefficient of resistance
If the resistance goes up – positive temperature coefficient (conductors)
If the resistance goes down – negative temperature coefficient (insulators and semiconductors)
How does temperature affect resistance?
Rh = Rc [1 + (α x Δt)]Where: Rh = Final (hot) resistance in ohmsRc = Initial (cold) resistance in ohmsα = Temperature coefficient of resistance in
omhs per ohms per degrees celciusΔt = difference in temperature in degrees
celcius
Equation for resistance and temperature
Most electrical components are made with a certain amount of smoke and if they get too hot it all gets let out!
Heat increases the resistance in conductors thereby increasing the voltage drop across the cable, also there is a risk of insulation meltdown – resulting in short circuit
Effects of temperature on a circuit
Motors, transformers, alternators and lamp filaments all start up with a lower resistance – leading to high starting currents.
R1 = ℓ1 hence R2 = R1 ℓ2
R2 ℓ2 ℓ1
But wait…..There’s more!
R1 = A2 hence R2 = R1 A1
R2 A1 A2
R1 = d22 hence R2 = R1 d1 2
R2 d12 d2
R2 = R1A1ℓ2
A2ℓ1
Series circuits