1. 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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. What is:
Open Circuit
Closed Circuit
Short Circuit

9. How to decode a resistor.

10. What is 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)

11. Linear resistors – wire wound

12. Linear resistors – carbon compound

13. Power ratings of res
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.

14. Tolerance and preferred values of resistance
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.

15. Non-linear resistors - Thermistors
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.

16. Non-linear resistors – Voltage dependant resistors (VDRs)
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.

17. Non-linear resistors – Light dependant resistors (LDRs)
Resistance varies as the light varies
Usually made from cadmium sulphide mounted on a plate and covered with a vacuum-deposited metallic grid

18. Resistor circuit symbols
Resistor (general)
Variable resistor (rheostat)
Variable resistor (potentionometer)
Adjustable resistor
PTC thermistor
NTC thermistor
Voltage dependant resistor
Light dependant resistor
+ to C
- to C

19. Remembering the resistor colour code
Black Beer Rots Our Young Guts But Vodka Goes Well
Black is NO color - nothing, zero Brown, 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 bill Blue, 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

20. How does length affect resistance?
Longer conductor =

21. How does length affect resistance?
Longer conductor = more resistance
Shorter conductor =

22. How does length affect resistance?
Longer conductor = more resistance
Shorter conductor = less resistance

23. How does length affect resistance?
Longer conductor = more resistance
Shorter conductor = less resistance
Resistance α Length

24. Conductor cross sectional area

25. How does c.s.a. affect resistance?
Larger conductor =

26. How does c.s.a. affect resistance?
Larger conductor = less resistance
Smaller conductor =

27. How does c.s.a. affect resistance?
Larger conductor = less resistance
Smaller conductor = more resistance

28. How does c.s.a. affect resistance?
Larger conductor = less resistance
Smaller conductor = more resistance
Resistance α
c.s.a

29. How does the conductor material affect resistance?
The measure of how resistive a material is, is called resistivity.
1 m Ω

30. Sooo… If we put all of them together…..
R = ρ x ℓ A
Where:
R = resistance of conductor in ohms
ρ = resistivity of conductors in ohm meters
ℓ = length of conductor in meters
A = c.s.a. of conductor in meters2

31. How does temperature affect resistance?
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)

32. Equation for resistance and temperature
Rh = Rc [1 + (α x Δt)]
Where:
Rh = Final (hot) resistance in ohms
Rc = Initial (cold) resistance in ohms
α = Temperature coefficient of resistance in omhs per ohms per degrees celcius
Δt = difference in temperature in degrees celcius

33. Effects of temperature on a circuit
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
Motors, transformers, alternators and lamp filaments all start up with a lower resistance – leading to high starting currents.

34. But wait….. There’s more! R1 = d22 hence R2 = R1 d1 2 R2 d12 d2
R1 = A2 hence R2 = R1 A1
R2 A A2
R1 = ℓ1 hence R2 = R1 ℓ2 R2 ℓ2 ℓ1
R1 = d22 hence R2 = R1 d1 2
R2 d d2
R2 = R1A1ℓ2
A2ℓ1

35. Series circuits