Topic 2 Basics of Energy and Power

7/29/2019 Topic 2 Basics of Energy and Power

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Topic 2: Basics of Power and Energy

Powervs. Energy

Important Power Values (k = kilo, M = mega, G = giga, T = tera)

"Caveman" ~ 100 W, U.S. per capita ~ 10 kW,

Windmill ~ 1 MW, Nuclear power plant ~ 1 GW

Total U.S. ~ 3 TW, Total world ~ 15 TW

U.S. energy consumption

Sectors: industrial, transportation, residential, commercial

Sources: oil, coal, natural gas, nuclear, hydroelectric, etc.

Types of Energy

Kinetic, Gravitational Potential, Thermal, Electrical


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Power vs. Energy

POWER = RATE of energy consumption = energy per unit time

Units of watts (1 W = 1 Joule/sec) or kilowatts (1 kW = 1 kJ / sec)

What is the U.S. per capita power consumption?

(a) 100 W (one 100 W bulb ALWAYS on)

(b) 10 kW (ten 1 kW hair dryers ALWAYS on)

ENERGY = power time

Units ofkilowatt-hours (kWh) or kilojoules (kJ)

1 kWh = 3,600 kJ (see notes section on PPT slide for calculation)


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Power Values

Power delivered to the Earth by the Sun equals 100,000 terawatts (TW)

or 1017

watts (W).One terawatt (TW) equals how many watts (W)?

(a) 1 million watts (106 W)

(b) 1 billion watts (109 W)

(c) 1 trillion watts (1012

W)

What is the total power consumption of the world's ~7 billion people?

(a) 1 TW (b) 15 TW (c) 100 TW

The per capita power consumption for the world is __________than the per capita power consumption in the U.S.

(a) higher (b) lower

(see notes section on PPT slide for calculation)


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Caveman

(2,000 kcal/day)

=Power = Energy per unit time = Watts (Joule/sec)

POWER = 100 Watts

ONE Light Bulb

Abouthow much does it cost to run a 100 W light bulb for one year?

(a) $1 (b) $10 (c) $100

(see notes section on PPT slide for calculation)


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U.S. "per capita"

=

POWER = 10 Kilowatts (kW)

100

10 000 Watts

or 10 hair dryers!


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=

ONE Windmill

POWER = 1 Megawatt (MW)

100

1 000 000 Watts


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ONE Nuclear Power Plant

= 1,000

POWER = 1 Gigawatt (GW)

1 000 000 000 Watts


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Power and Consumed Energy Cost

A 100-watt light bulb costs approximately $100 to run for one year.

Using the same pricing ($1 per watt for 1 yr usage), what is the "cost"

for the energy produced in one year by a 1-GW nuclear reactor?(a) $100 million

(b) $1 billion

(c) $10 billion

The unit of "wattyr" (or 1 watt for 1 year) is a unit of:

(a) Power (b) Energy


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U.S. Energy Consumption

Transportation

28%

21%Residential

18%Commercial

33%

Industrial1 2

34

What sectors can you

directly impact?


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U.S. Energy Sources

What percent of U.S. energy comes from fossil fuels? (2-digit answer)

Natural Gas

23%

23%

Coal

39%

Oil

8%

Nuclear

Rank the following sources for

total U.S. energy from largest tosmallest. (4-digit answer)

(a) Hydroelectic

(b) Coal or Natural Gas

(c) Oil

(d) Nuclear


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World Energy Consumption per Capita

http://commons.wikimedia.org/wiki/Image:Energy-consumption-per-capita-2003.png

What countries have very high (red!) per capita energy consumption?

(Enter ALL in NUMERIC order)

(1) U.S. (2) Australia (3) Japan (4) Russia (5) Saudi Arabia


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Types of Energy

Kinetic (KE) = energy ofmotion of objects

Potential (PE) = energy ofposition

Thermal = energy ofmotion of atoms or molecules

Electrical = energy ofcurrent flowing in a circuit

Chemical = energy of atomic and molecular bonds

Nuclear = energy from breaking or joining nuclei


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Potential & Kinetic Energy

As a rock falls, its potential energy PE is

convertedinto kinetic energy KE.

Due to energy conservation,

the rocks total PEat the top equals

its KEjust BEFORE hitting the ground.

What type of energy does the rock haveAFTER it hits the ground?

(a) kinetic

(b) potential

(c) neither (converted to thermal energy)

Figure from Giancoli

All PE

All KEBEFORE hitting

HalfPEHalfKE

(assume PE = 0 atground height)


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Motion on a U-track

Which energy is maximum at the bottom? (a) kinetic (b) potential


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Potential Energy

Gravitational potential energy PEis the energy associated with the height

of an object from the ground.

PE equals the objects mass m times its height htimes its gravitational

acceleration g(= 10 m/s2).PE hmg

If the height of a ball is tripled, then how many times larger is its

potential energy?


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Simple Generator (Phet animation)

What is the order of the types of energy starting from the falling water

and ending with the lightbulb? (4-digit answer)

(a) electrical energy

(b) potential energy (gravitational)

(c) light energy

(d) kinetic energy


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Hydropower uses the gravitational potential energy from falling water.

Higher head (height difference) and flow rate give higher power.

If the height of the dam is doubled, then the energy output is how

many times larger? (a) 1.5 times (b) 2 times (c) 4 times

Hydroelectric Dam

Initial Height

Final Height


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Kinetic Energy

Kinetic energy KEis the energy ofmotion for an object.

Kinetic energy equals one-half the objects mass m times its velocity v

(or speed) SQUARED.

1

2

2KE mv

If the speed of a car is doubled, then its kinetic energy is four times

larger (equals 2 x 2).

If the speed of a car is tripled, then how many times larger is its

kinetic energy?

A car at 70 mph has

TWICE the kinetic

energy than at 50 mph!

S d M i d E li h U i


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Speed: Metric and English Units

Quick conversion from m/s to mph: double and THEN add 10%

If a car travels at 30 m/s, then how fast is that in mph?

Do it in your head!

If a sprinter runs at 10 m/s, then what is her speed in mph?

1 mile 3600 s10 1609 m 1

m 22 miles/hrs

hr

Ki ti E f C


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Kinetic Energy of Car

If a 1000-kg car travels at 66 mph (or 30 m/s), then find its kinetic

energy in kilojoules (kJ).

12

2 UNITS: in kg, in m/s, in Jm v m v KE KE

El t i l E


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Electrical Energy

Today, end-use electrical energy consumption is 13% of total U.S.

energy consumption. But more energy is needed to generate electricity

because of inefficiencies.It takes about 3 kW of input power to generate 1 kW of electrical

power. Approximately what percentage of total U.S. energy is then

used to GENERATE end-use electrical energy?

(a) 20% (b) 30% (c) 40%

%e

lectricalenergy

1950 2000

13%

3%

END-USE Electrical Energy

Consumption

U S E S f El t i it


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U.S. Energy Sources for Electricity

Natural Gas

18%

50%

Coal

3%

Oil

Rank the following sources forU.S. electrical energy from largest

to smallest. (4-digit answer)

(a) Hydroelectic

(b) Nuclear or Natural Gas

(c) Oil(d) Coal

Nuclear

20%

7%

Hydro

Hi t f El t i it


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History of ElectricityAncient societies knew of electric chargeelectric eels, rubbing amber

caused materials to stick (Greek word for amber = elektron)

What attractive force acts between materials rubbed with amber?(a) gravitational (b) electrostatic (c) strong nuclear

William Gilbert (1544-1603)coined term electricity

Hi t f El t i it


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History of Electricity

Benjamin Franklin (1752): experiments with electricity/lightning

Luigi Galvanimade legs of dead frogs move with dissimilar electrodes

Alessandro Volta (1791-1800) - built a voltaic pile (early battery)

Franklin thought that positive charge flowed in wires. Was he right?

(a) yes (b) no

Voltaic Pile

El t i Ch


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Electric Charge

What are the positively charged particles in matter?

What are the negatively charge particles in matter?What particles flow in wires to create electric current?

(3-digit answer)

(1) electrons (2) neutrons (3) protons (4) positrons

St ti El t i it (Ph t i ti )


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Static Electricity (Phet animation)

If two DIFFERENT materials touch each other, then electrons move

from one material to the other because one material gives up

electrons easier.

If electrons move between objects, then the objects become oppositely

charged and _________ each other.

(a) repel (b) attract.

Positive Hair

+ + ++

Electrons movefrom hair to balloon

Negative Balloon

Static Electricit (Ph t i ti )


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Static Electricity (Phet animation)

When Travolta rubs his foot on the carpet, ______ are transferred

between the carpet and his body.

When Travolta then touches the door knob, _______ move between

his charged body and the grounded door. It can hurt!

(1) electrons (2) protons (2-digit answer)

Light Bulb Circuit (Ph t i ti )


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Light Bulb Circuit (Phet animation)

Electrical current = motion of electrons (units of Amperes or A)

Electrical voltage = difference in charge causing current (Volts or V)

In the light bulb circuit, how do the electrons move in the wires?

(a) from (+) to () OR (b) from () to (+) battery terminal

What is the voltage of a D-cell battery? (a) 1.5 V (b) 6 V

battery

wire

light bulb

Resistor Circuit (Ph t i ti )


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Resistor Circuit (Phet animation)

When the battery voltage is increased, the current ________ .

When the circuit resistance is increased, the current ________ .

(1) increases (2) decreases (2-digit answer)

Electric Oven to Cook a Turkey


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Electric Oven to Cook a Turkey

If a 5,000 watt electric oven is on for 10 hours to cook a turkey, how

many kilowatt-hours (kW-hrs) of energy is used?

If the power company charges 10 per kWh, then how much did it

cost in dollars to cook your turkey?

Topic 2 Basics of Energy and Power

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