1. 1

2. 2

3. 3

4. Types of current: Direct and Alternating
Direct current(DC)
Produced by ……… and …………….
Has a ……………….. flow of charges
The current intensity and voltage are……………

5. Types of current: Direct and Alternating
Alternating current(~ or AC)
Produced by ………… companies (Hydro Quebec)
Has ……………...flow of charges (pendulum-oscillation)
The ……………... and the……… intensity alternate (oscillate) between their respective maximum and minimum values.

6. The number of oscillation per unit time(second) is called the …………(Hertz); 60Hz for North America and 50Hz for Europe

7. 9

8. 10

9. The Voltage increases and peaks at +170 volts.
1 cycle
+170v
The Voltage increases and peaks at +170 volts.
time
-170v
The Voltage decreases and peaks at -170 volts. 11

10. Vrms = 0.707Vmax Pav= Irms Vrms Irms = 0.707Ipeak
Since the voltage and the current intensity alternate (oscillate) between their respective maximum and minimum values,
The root-mean-square values of the voltage and the current intensity are used for analyzing AC circuits.
Irms = 0.707Ipeak
Vrms = 0.707Vmax
Pav= Irms Vrms

11. It represents the average value of a Sinusoidal waveform.
RMS stands for::
Root Mean Square
It represents the average value of a Sinusoidal waveform.

12. This stands for the area under the curve.
rms = Root Mean Square
This stands for the area under the curve.
For either voltage or current.
+170v
2 / 2 = 0.707
time
-170v

13. A desktop computer operates on 115 Vrms
Between which two voltages does its voltage oscillate?
Determine the peak and rms Currents if it draws 650 W.

14. Adopting Voltage A transformer
is used to increase (step-up) or decrease (step down) the voltage of the power source.
In a transformer the …… power (at the primary) is equal to the ……………… power (at the secondary)
the number of turns at the primary and the secondary are ………………………. to their respectively voltages

15. Adopting Voltage A transformer Pprimary = Psecondary P1=P2
is used to increase (step-up) or decrease (step down) the voltage of the power source.
Pprimary = Psecondary
P1=P2

16. Adopting Voltage A transformer Pprimary = Psecondary P1=P2 V1I1=V2I2
is used to increase (step-up) or decrease (step down) the voltage of the power source.
Pprimary = Psecondary
P1=P2
V1I1=V2I2
N1V2=N2V1

17. Adopting Voltage Rectifiers Inverters
Convert alternating current to direct current with very little to no lost in energy.
Inverters
Convert direct current to alternating current with very little to no lost in energy.

18. 15

20. A 240Vac source powers a transformer with 400 turns at the primary and 80 turns at the secondary.
Calculate the voltage at the output of the transformer.
Is it a step up or a step down transformer? Justify your answer.
What happens to the output voltage when the number of turns at the secondary is decreased by half?
What is the output current if the current at the input is 5A?
Between which two Amperages does the current oscillate at the output?
What is the power at the input?

21. Residential electrical installation

22. 17

24. ON
OFF
2 x 120v
Ground
0 - Gnd

25. 18

26. +170
-170
+340
+170
-170
-340

27. Distribution inside the house
General purpose branch circuit
Powers several parallel circuit outlets
Potential difference of 120V
15A current
Many outlets are connected on the same general purpose branch circuit if low power is required or they are never used simultaneously.

28. Distribution inside the house
Single purpose branch circuit
Powers single outlets
Electric range and cloth dryers
Potential difference of 240V
30A or more current intensity

29. Conductors used in distribution lines
American Wire Gage (AWG) System
The AWG number of a conductor is an indication of its resistance. The resistance of a wire is proportional to its AWG number; the lower the AWG number the lower the resistance.
Four properties of conductors are considered as they determine the resistance of the wire: the type of metal, the length, the diameter of the wire and the temperature.

30. Which of the wires above has the highest Resistance?
Which can carry the most current?
A Circuit has been started with an 12-AWG wire, unfortunately it is not enough to complete the job. Which wire, 8-AWG or 14-AWG , can be used to complete the circuit without having any impact on the flow of current? Explain your answer. 23

31. 24

32. The AC Socket The Larger prong is called the Return.
White
The smaller prong is called the ‘Hot’.
Black
This is the Gnd

33. 120 v, 15A
120 v
15A

34. 25

36. 28

37. 29

39. 29

40. 31

41. Ground - bare
Live - Red
Live - Black
Return- White 32

42. 31

43. 39

47. -Require both High and low Currents & Voltages
Industrial circuits:
-Complex
-Require both High and low Currents & Voltages 42

48. 44

49. Ex 4.31:
Calculate the percent efficiency of the direct-current transmission line between James Bay and New England if it offers a resistance of ohm/km MW is transmited at 450kV over a 1513 km distance. 50

50. The human body is a conductor (~70% water) with variable resistance (500-1000Ω)
A body that is subjected to a potential difference will have an electrical shock .
The shock current depends on the resistance of the body and the resistance of the contact.
A wet hand has a much lower ( times) contact resistance than a dry hands 51

51. The current intensity that runs through the body determines the consequences of an electric shock.

53. The ground of a plug serves to send excess charges (or charges on the casing) to the earth.
Appliances with metal casing or metallic parts that are easily accessible to the user require a ground.

56. Some Questions…..next page
End of Chapter
Some Questions…..next page

57. With the current I=287mA, it is dangersouly higher than 80mA
= Ω
I = V / R = 14.5 x 103 V / Ω = A = 287mA
With the current I=287mA, it is dangersouly higher than 80mA
and the person might be killed.
Several different ways:
Cut the parachute and jump.
Wait for help.
Use insulation from the harness to climb down without touching the wires .... 55

58. Washing machines, refrigerators have 3-prong plugs.
They are appliances with a metal casing.
Their casings are made of plastic or other insulating material.
The current that passes through the body.
Because the current also becomes greater with higher voltage across the body.

59. False
True
False
True 56

60. True
False
False
False 57

61. True
False
True
False

62. False
True
False
True 58

63. True
False

64. I = P / V = W = 2A
60 V
I = P / V = W = 2A
60 V
Vpeak = Vrms = 60V = 85V
Ipeak = Irms / = 2A/ = 2.8A

65. Ground 1 = 0 Neutral 2 – 120Vrms 3 – 120Vrms AC Voltage
Root mean square
Between either live bus bar and the neutral bus bar.
The dryer requires 240V for the heating element and 120V for the motor.
This requires: 2 wires for the live wires for 240V and 120V.
1 wire for the return line for the 120 and 1 wire for the ground.
Ground 62

66. This is capable of providing both outlets on the socket with a separate 15A branch feed.
No because the appliances in the kitchen require more current than those in other rooms.

67. 15 A
P = VI = 120V x 15A W
50 MW
No it is less. In a transformer a higher voltage results in a lower current in the secondary.
By reducing the current, then the power lost due to the joule effect (P=I2R) is reduced. 63

68. Appliances with metal bodies require the casing to be grounded and therefore the three prong plug is required.
False
False
False

69. True
False
True
False 64