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Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

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Page 1: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Lecture 1

1.2 SI Units1.4 Voltage and Current1.6 Power and Energy

Page 2: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

SI Units

Page 3: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Derived Units in SI

Page 4: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Standardized Prefixes

Page 5: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Exercise 1

How many hours of video will fit in a 32 GB memory? Assume the followings:• 1 GB=210 Bytes• 480 x 320 Pixels per Frame• 2 bytes per Pixel• Rate of display: 30 Frames per Second

Page 6: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Solution

• 480 x 320 [Pixels/Frame] x 2 [Bytes/Pixel] x 30 [Frames/Second]=9,216,000 Bytes/Second

• 9,216,000 Bytes/Second=30.89 GB/Hour• 32 GB/(30.89 GB/Hour)=1.035 Hour=62

minutes

Page 7: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Exercise 2

• If a signal can travel in a cable at 80% of the speed of light, what length of cable, in inches, represents 1 ns?–Assume the speed of light is 3 x 108

m/s

Page 8: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Solution

• 80 % of speed of light is 2.4 x 108 m/S• 2.4 x 108 m/S x 10-9 S=0.24 m=24 cm• 2.54 cm =1 inch• 24 cm/2.54 cm=9.45 in 1 nS

Page 9: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Voltage and Current

Page 10: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Learning by discovery

Page 11: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Experience Electricity

• The sudden sharp tingle that you feel is caused by electricity from one terminal of the battery, through the moisture on and in your tongue, to the other terminal.

• Because the skin of your tongue is very thin and the nerves are close to the surface, you can feel the electricity easily.

• Warnings: Do not do this experiment at home

Page 12: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Movement of Electrons

• The sharp tingle you feel is caused by an electric current.

• An electric current is caused by the movement of electrons.

• The movement of electrons is caused by the battery.

Page 13: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Attraction/Repulsion

Page 14: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Definition of Voltage

• Voltage is the energy per unit charge created by the separation

𝑉=𝑑𝑊𝑑𝑄

Page 15: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Intuition

• Thought Experiments:–Assume V is fixed. Hold 2 X of Q in

your hand. Spend 2X of energy to move 2Q from –Q to Q.

–Assume Q is fixed. Increase V by 2X. Spend 2X of energy to move Q from –Q to Q.

Page 16: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Definition of Current

• Current = the rate of charge flow

Page 17: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Intuition about Current

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Direction of Current

Page 19: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Water Flow Analogy

Page 20: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Definition of Energy

• Energy (W)is the ability to do work.–The unit of energy is Joules (J).

Page 21: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Energy Example

Page 22: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Definition of Power

• Power is the rate at which energy is used

• Unit of Power: Watts

Page 23: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Example of Power

• 360 J of energy is required to operate an MP3 player for an hour. What is the average power consumption?–1 hour=3600 seconds–360 J/3600 seconds=0.1 W or 100 mW

Page 24: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Analogy

Tank=batteryThe height of the water=voltageThe volume of flow through the hole per second=currentThe smallness of the hole=resistanceWater wheel hit by the flow from the hole=power

Page 25: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Thought Experiment #1

Fix the dimension of the holeAdd more water →V↑→I↑→P↑

Page 26: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Thought Experiment #2

Fix the height of water in the tank (Voltage is fixed)Increase the hole dimension →I ↑→P↑.

Page 27: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

How do you measure power?

Page 28: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Power consumed by typical House appliances

Appliance Power (Watts)Toaster 712Waffle maker 1150Projector 192Refrigerator 130Microwave 1610Hair dryer 1532Cable modem 8Wireless router 9

Internet phone 4TV (25 inch, analog) 70

Page 29: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Devices can consume power even when they are not used

Bose speaker 7 WattsProjector 7 WattsMicrowave 6 WattsRechargeable shaver 3 WattsToaster 3 WattsTV 3 Watts

Point of comparison: MP3 player consumes 0.1 Watts

Page 30: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Power Consumed by Lights

14 lights on each floor.Each light bulb consumes about 20 Watts.There are 8 floors.20 Watts x 14 x 8=2240 Watts !!

Page 31: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Caution!

• Power is not the same as energy.• Power is the rate at which energy is being

used.• Example

– TV consumes 70 Watts or 70 Joules per second.– How much energy is consumed by 1 hour of TV vs

40 hours of TV?

Page 32: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

kWh

• There is another way to express energy.• Since P=W/t, Energy (W) can be expressed as

W=Pt• Utility companies charged their customers by

kWh

Page 33: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Example 4-3

• Determine the number of kilowatt-hours (kWh) for each of the following energy consumption:– 1400 W for 1 hour– 2500 W for 2 hours– 100,000 W for 5 hours

Page 34: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Energy Consumed by Typical Household Appliances

Wireless router and cable modem:1. Consumes little power.2. Consume more energy than you think.

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Energy Consumed by OFF Devices

My toaster consumes more energy when it is off!!

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Cost

• Delivery charges: Cost of delivery electricity to homes. ($0.26 per kWh)

• Generation charges: cost of purchasing electricity. ($0.09 per kWh)

• Total cost per kWh. (0.35 per kWh)

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Cost of typical household items

Even though it may cost just a few pennies a day, over the cost of 1 year,the cost can skyrocket pretty quickly.

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Cost of Not Unplugging the OFF devices.

Each device may not consume much power in its off state.But over the course of one year it can be expensive.

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Cost of Not turning Lights Off

Our condo can save as much as 2300 a year if we only turn them on at night.

Page 40: Lecture 1 1.2 SI Units 1.4 Voltage and Current 1.6 Power and Energy

Electric Car

• PG&E says that the E-9 rate is mandatory for those customers who plan on refueling an EV on their premises.

• Driving Tesla 40 miles a day would use 11.2 kW-h.– Electricity cost: between $0.56 and $3.18

depending on the time of day chosen for recharging.

• Driving an internal combustion engine car for 40 miles a day at 25 mpg would use 1.6 gallons of gas, and at a cost of 3 dollars per gallon would cost 4.80.