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# Energy and Radiation - PowerPoint PPT Presentation

Energy and Radiation. Science Concepts Definition Potential Kinetic Radiant Radiation Wave Equation Spectrum Stefan-Boltzmann Law Wein’s Displacement Law Conduction Convection. Energy Energy Types Temperature Driven Heat Transport. The Earth System (Kump, Kastin & Crane)

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Presentation Transcript

Science Concepts

Definition

Potential

Kinetic

Wave Equation

Spectrum

Stefan-Boltzmann Law

Wein’s Displacement Law

Conduction

Convection

Energy

Energy Types

Temperature Driven Heat Transport

The Earth System (Kump, Kastin & Crane)

• Chap. 3 (pp. 34-41; pp. 45-46)

What happens when we drop an object?

What happens when water behind a dam spills to the river below?

What happens when wood burns?

What happens when we turn on a flashlight?

Definition

• Energy is the ability to do work

- Work = Force • Distance

- Units

> 1 calorie = energy required to heat 1 gm of water 1°C

‡ Note: 1 Calorie (capital C) = 1000 calories = 1 kilocalorie

◊ Unit for food derived energy

Types of Energy

• Potential

- Chemical

> Example: a fire

- Electrical

> Voltage

‡ Example: a battery uses chemical potential energy to create a

voltage and therefore electrical potential energy

Types of Energy (Con’t)

• Potential (Con’t)

- Gravitational

> Result of object's relative position

‡ Example: a falling rock

‡ Example: cold (dense) air (fluid) next to warm (less dense)

air (fluid)

• Kinetic

- Result of an object's motion

- Large-scale motion

> Example: falling water (hydroelectric power generation)

> Example: swinging hammer (drive nail)

> Example: air motions, i.e., wind

- Micro-scale motion

> Example: molecular vibration or temperature. Also called thermal

energy

“It is like the advent of thermodynamics … in about 1820. They knew there was something called ‘heat,’ but they were talking about it in terms that would later sound ridiculous.” In fact, he says, they weren’t even sure what heat was, much less how it worked. Most reputable scientists of the day were convinced that a red-hot poker, say, was densely laden with a weightless, invisible fluid known as caloric, which would flow out of the poker into cooler, less caloric-rich bodies at the slightest opportunity. Only a minority thought that heat might represent some kind of microscopic motion in the poker’s atoms. (The minority was right.)

Waldrop, M.M., 1992: Complexity-The Emerging Science at the Edge of Order and Chaos, Touchstone, pp. 297-298.

Types of Energy (Con’t)

from a fire in a

fireplace

from the Sun

Definition

• Heat - Energy in transit

because of a temperature

difference

Would walk up and pick up this frying pan?

And this one ?

Three Mechanisms

• Conduction - Objects in contact;

molecules bouncing off each

other; solids

• Convection - Motion; hot air rises;

gases and liquids

requiring a medium; vacuum;

Electromagnetic waves

Three Mechanisms (Con’t)

• Conduction - Objects in contact; molecules bouncing off each other; solids

- Caused by uneven temperature

> Examples:

Heat conductivity

Material( cal / s - cm - °C )

Air (at 0°C) 0.000058

Air (at 20°C) 0.0000614

Dry soil 0.0006

Dry sand 0.0013

Water (at 10°C) 0.00143

Concrete 0.0022

Wet soil 0.0050

Ice (at 0°C) 0.0054

Steel 0.121

Iron 0.161

Aluminum 0.50

Copper 0.918

• Conduction (Con’t)

- New fresh, light snow - Good insulator because of trapped air

- Older settled or wet snow - Not as good an insulator

1.0

0.9

0.8

0.7

0.6

Snow Density ( g / cm3 )

0.5

0.4

0.3

0.2

0.1

0

0

0.001

0.002

0.003

0.004

0.005

Conductivity in Snow ( cal / s - cm - °C)

Factoid -

An oil lamp with a hollow wick burns 10 times brighter than a lamp with a solid wick

Three Mechanisms (Con’t)

• Convection - Motion; hot air rises; gases and liquids

- Caused by uneven heating of fluids

- Thermal circulations; Many sizes

> Clouds

‡ Convective clouds - cumulus cell

> Sea breeze

> Monsoon - India and Arizona

> Global circulation

Effect of convection on flames -

Left image (with gravity, i.e., convection)

Right image (low gravity in space, i.e., little convection)

http://microgravity.grc.nasa.gov/combustion/cfm/cfm_index.htm

Amplitude

Height

Trough

Wavelength

Heat - Energy Transfer (Con’t)

Three Mechanisms (Con’t)

- Transfer without requiring a medium; vacuum; Electromagnetic waves

- All objects with temperature above absolute zero emit radiation

- The analogy of waves is often used to describe radiation

Three Mechanisms (Con’t)

- The analogy of waves is often used to describe radiation

> Wave Equation

‡ Example: Boat dock

‡ Speed of wave = wavelength * frequency

or

frequency = Speed of wave / wavelength

where ( Speed of wave ) for radiation is the speed of light which

equals 3 x 108 m / s

Frequency Units -

RPM - Revolutions /

minute

Hertz - cycles / sec

(hertz)

Wavelength

(m)

23

-14

10

10

Gamma

Rays

-10

10

18

10

X Rays

-6

10

Ultraviolet

14

10

Visible

Infrared

-2

10

Microwaves

10

10

1

TV

2

10

TV - FM

Short-wave

6

10

6

10

Long - Wave

2

10

1

Heat - Energy Transfer (Con’t)

Three Mechanisms (Con’t)

- Radiation from materials is emitted with a range

of wavelengths, i.e., a spectrum of wavelengths

“He recognized the model, and knew it was a state-of-the-art microwave protection system. Mounted on each sturdy pole beneath an aluminum hood was a dieletric transmitter and a receiver; a 15 GHz signal was set to one of several selectable AM signal patterns.”

Ludlum, Robert, 2002: The Janson Directive. p. 449.

NOTE:

GHz = gigahertz = 109 Hz

Three Mechanisms (Con’t)

- Visible range from 0.4 to 0.7 microns

NOTE:

10-6 m = m

= micron

http://observe.arc.nasa.gov/nasa/education/reference/reflect/ir.html

Why is a red shirt red?

Why is a white shirt white?

Why is a black shirt black?

Why is a red flame red?

Why is a blue flame blue?

Three Mechanisms (Con’t)

• Compare these two statements. Are they correct physics?

“The music was so loud, it was almost like no sound, like silence, in the

same way that black is every color intensified into nothing.”

“K” is For Killer - Sue Grafton (p. 251)

“ ‘All colors taken together congeal to whiteness, the greatest part of space

is black,’ say the journal notes.”

Golf in the Kingdom - Michael Murphy (p. 130)

(10 m)

-9

18

10

10

-6

10

14

-5

10

10

13

10

Heat - Energy Transfer (Con’t)

Three Mechanisms (Con’t)

- Ultraviolet (uv) C -Shortest wavelength; Most powerful; Filtered by the

ozone layer

- uv B - Midrange uv; Less powerful; Produces both suntans and burns;

Energy dissipated in outer layer of skin; Causes painful burns;

Contributes to skin cancer; Do not penetrate glass

- uv A - Longer wavelength uv; Penetrates deeply into skin; causes

longterm damage; Causes premature aging; Adds to harmful effects of

uv B; Can penetrate glass

Wavelength

Frequency

Wavelength

(hertz)

(m)

0.20

uv

C

Expanded

0.29

Ultraviolet

Ultraviolet

uv

B

0.32

Wavelengths

uv

A

Visible

0.40

Three Mechanisms (Con’t)

- Radiation from materials is emitted with a range of wavelengths,

i.e., a spectrum of wavelengths (Con’t)

Exam Scores

20

18

16

14

12

10

Number of Students per Grade Interval

8

6

4

2

0

0

10

20

30

40

50

60

70

80

90

100

17,500



max

15,000

12,500

(Cal - cm-2 - min - mm -1 )

10,000

7,500

5,000

2,500

0

0.0

0.5

1.0

1.5

2.0

Wavelength (

m)

m

Heat - Energy Transfer (Con’t)

Three Mechanisms (Con’t)

- What is the Sun’s spectrum?

> Below is the Sun’s emitted radiation spectrum; assumes the Sun’s

outer surface temperature is 6000 K

Note: 1 calorie =

energy required to

heat 1 gm of water

1°C

Note: 1 Calorie

(capital C; Unit

used for food

derived energy) =

1000 calories

(lower case c) =

1 kilocalorie

Note: The Sun emits much of it’s radiation in the visible range with its wavelength of maximum emission, (max), is about 0.48 m, i.e., in the blue-green range

95% of the Sun’s emitted radiation is in the region between 0.25 and 2.5 m

Three Mechanisms (Con’t)

- What is the Earth’s spectrum?

> Below is the Earth’s emitted radiation spectrum; assumes the

Earth’s surface temperature is 288 K

Note: Energy amounts per wavelength interval much smaller than for the Sun

Note: The Earth’s wavelength of maximum emission, (max), is about 9.8 m

max

0.050

95% of the Earth’s emitted radiation (gray area) is in the region between 2.5 and 25 m, i.e., at much longer wavelengths

Per Wavelength Interval

(Cal - cm-2 - min - mm -1 )

0.025

0

30

20

0

10

Wavelength (

m)

m

Stefan-Boltzmann Law

• The Total Radiation per unit area is directly proportional to

the object’s absolute temperature to the fourth power, i.e.,

R = (Const) * T4 = (Const) * ( T * T * T * T )

where T is the temperature in Kelvin and the constant

equals 5.67 x 10-8 watts / ( m2 K4 ).

Ludwig Boltzmann 1844-1906

http://www-groups.dcs.st-and.ac.uk/

~history//Mathematicians/Boltzmann.html

Josef Stefan 1835-1893

http://www-groups.dcs.st-and.ac.uk/

~history//Mathematicians/Stefan_Josef.html

Stefan-Boltzmann Law

• Examples:

- For the Sun: T = 6000K

R(Sun) = 5.67 x 10-8 W / (m2 K4 ) * ( 6000K )4

= 7.35 x 107 W / m2

- For the Earth: T = 300K

R(Earth) = 5.67 x 10-8 W / (m2 K4 ) * ( 300K )4

= 4.6 x 102 W / m2

Wien's Displacement Law

• Wavelength of the maximum energy times the object’s

temperature equals a constant

max* T = Const

where max is the wavelength of maximum energy, T is

temperature in Kelvin and the constant equals

2.89 x 10-3 meter Kelvin.

Wilhelm Wien 1864-1928

http://www-gap.dcs.st-and.ac.uk/

~history/PictDisplay/Wien.html

Wien's Displacement Law

• Examples:

- For the Sun: T = 6000K

max (Sun) = Wavelength of maximum energy (Sun)

= ( 2.89 x 10-3 m K ) / ( 6000K ) = 0.48 x 10-6 m

= 0.48 microns

- For the Earth: T = 300K

max(Earth)

= ( 2.89 x 10-3 m K ) / ( 300K )

= 9.6 microns

Summary

• Sun emits 1.6 x 105 more energy per area than the Earth emits

• The Sun’s energy spectrum is centered in the visible region while the Earth’s

energy spectrum is centered in the infrared range

• 95% of the Sun’s radiation is in the region between 0.25 and 2.5 microns

while 95% of the Earth’s radiation is in the region between 2.5 and 25

microns