Phys 150 Lecture 1 1

• Please sit together in pairs:

– Onyema and Honglu– Alejandra and Sean– Chris and Lin– Rachel and Anwen– John F. and Mengyue– Walter and Melissa– Max and Zhongyun– Matt and Anna– Amanda and Kaijun– Pauline and Erich– Jacob and Irfan– John W. and Michael – Jennifer and Jiayuan

– Alexandra and Erica– Emmanuel and Dian– Robert and David– Andrew and Shiying

Phys 150 Lecture 2 2

Announcements• Chapters 1 and 2 are available online

(see the 150 web page).• There will be a Quiz on Chapter 1 on

Tuesday at the beginning of class.• Homework 1 is due on Sunday at

midnight. Please go to the 150 web page and click on Course Schedule.

• i>clickers are required starting Tuesday. Please register via the 150 web page.

Phys 150 Lecture 2 3

Explosions Cannon

• Rapidly expanding hot gas

Phys 150 Lecture 2 4

Explosions Cannon

• Rapidly expanding hot gas

Comet Shoemaker-Levy 9 1994

Phys 150 Lecture 2 5

Explosions

Extinction of dinosaurs 65 million years ago

• Kinetic energy = energy of motion = ½ mv2

Phys 150 Lecture 2 6

Power• 60 Watt incandescent light bulb

– Most of the power is producing heat, not light

• 13 Watt Compact Fluorescent Light (CFL)– Same light output with 1/4 the energy use

• 10 Watt Light Emitting Diode (LED) – Same light output with 1/6 the energy use!

Power = Energy/Time Watt = Joules/sec

Bulbs

Phys 150 Lecture 2 7

Power• 60 Watt incandescent light bulb

– Most of the power is producing heat, not light

• 13 Watt Compact Fluorescent Light (CFL)– Same light output with 1/4 the energy use

• 10 Watt Light Emitting Diode (LED) – Same light output with 1/6 the energy use

Bulbs

Phys 150 Lecture 2 8

Electric energyA 10 Watt LED bulb running continuously

for one year (24 hrs/day x 365 days/yr = 8760 hours) uses10 Watts x 8760 hours

= 87,600 Watt-hours = 87.6 kilowatt-hours

• kilowatt-hour (kWh) is a commonly used unit of energy (kilowatt = 1000 Watts)

Phys 150 Lecture 2 9

Energy units• Calorie (Cal) – food and chemistry• kilowatt-hour (kWh) - electricity• British Thermal Unit (BTU) –

heating/cooling• Joules (J) – science

1000 Cal ≈ 1 kWh ≈ 4000 BTU

Phys 150 Lecture 2 10

i>clicker questionA typical house in the US requires about a kW of electric power. How much electric power do you need to power a million homes?

A. kilowattB. MegawattC. GigawattD. Terawatt

Phys 150 Lecture 2 11

i>clicker questionA typical house in the US requires about a kW of electric power. How much electric power do you need to power a million homes?

A. kilowatt (kW) = 1000 W = 103 WB. Megawatt (MW) = 1,000,000 W = 106 W

(million)C. Gigawatt (GW) = 1,000,000,000 W = 109 W

(billion)D. Terawatt (TW) = 1,000,000,000,000 W = 1012

W (trillion)A large electric power plant generates about a Gigawatt of electric power

Phys 150 Lecture 2 12

i>clicker questionA typical home in the US requires about a kW of electric power (without AC). How much electric power do you need to power a million homes?

kW x 1,000,000 = 1000 W x 1,000,000 = 1,000,000,000 W = Gigawatt

kW x 106 = 103 W x 106 = 109 W = Gigawatt

Calculator: 1 EE 3 x 1 EE 6 = 1 09

Phys 150 Lecture 2 13

Types of Energy• Chemical energy • Chemical energy• Heat energy = Thermal energy• Kinetic energy = energy of motion = ½

mv2

• Electric energy• Light energy• Nuclear energy ≈ 106 x chemical

energy

Phys 150 Lecture 2 14

Light energy• Light energy (solar energy) Solar

motor

Phys 150 Lecture 2 15

i>clicker questionThe amount of power in one square meter of sunlight (with the sun directly overhead) is about

A. 1000 BTUB. 1000 CaloriesC. 1 kWhD. 1 kW

Phys 150 Lecture 2 16

i>clicker questionThe amount of power in one square meter of sunlight (with the sun directly overhead) is about

A. 1000 BTUB. 1000 CaloriesC. 1 kWhD. 1 kW

meter2 of sunlight ≈ 1 kW

Phys 150 Lecture 2 17

Solar automobiles

• Typical automobile needs 50 – 400 hp Solar car meter2 of sunlight ≈ 1 kW ≈ 1 hp

Phys 150 Lecture 2 18

Solar airplanes

meter2 of sunlight ≈ 1 kW ≈ 1 hp

Zephyr – flew for 2 weeks

Zephyr

Phys 150 Lecture 2 19

1 kW ≈ 1 hp ≈ meter2 of sunlight

Phys 150 Lecture 2 20

i>clicker questionThe amount of power in one square kilometer of sunlight (with the sun directly overhead) is about

A. 1 kWB. 1 MWC. 1 GWD. 1 TW

Phys 150 Lecture 2 21

i>clicker questionThe amount of power in one square kilometer of sunlight (with the sun directly overhead) is about

A. 1 kWB. 1 MWC. 1 GWD. 1 TW

– km2 = 103 m x 103 m = 106 m2, so– km2 sunlight = 106 x kW = 106 x 103 W =

GW– Same as a large power plant

Phys 150 Lecture 2 22

Solar Photovoltaic (PV) cells• Inexpensive ones are 15% efficient• Expensive ones are 40% efficient

$325 Very expensive