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

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.

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

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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

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

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

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

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.

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

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

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

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.

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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?

Residential electrical installation

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ON OFF 2 x 120v Ground 0 - Gnd

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+170 -170 +340 +170 -170 -340

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.

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

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.

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

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

120 v, 15A 120 v 15A

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

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

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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 0.005 ohm/km . 2000MW is transmited at 450kV over a 1513 km distance. 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 (50 000 times) contact resistance than a dry hands 51

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

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.

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

With the current I=287mA, it is dangersouly higher than 80mA = 50500 Ω I = V / R = 14.5 x 103 V / 50500 Ω = 0.287A = 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

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.

False True False True 56

True False False False 57

True False True False

False True False True 58

True False

I = P / V = 120 W = 2A 60 V I = P / V = 120 W = 2A 60 V Vpeak = Vrms = 60V = 85V 0.707 0.707 Ipeak = Irms / 0.707 = 2A/0.707 = 2.8A

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

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.

15 A P = VI = 120V x 15A 1800W 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

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

True False True False 64