Protons for Breakfast

Week 3: Heat

November 2009

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In the event ofan alarm…

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How it all fits together…

Electromagnetic waves

Atoms

Heat

Electricity

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Tonight’s talk

• Atoms and molecules are ceaselessly moving

• Temperature is a measure of how fast the atoms and molecules are moving

• Atoms and molecules are constantly emitting and absorbing electromagnetic waves

• The frequency of the waves emitted and absorbed depends on temperature

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Key fact to remember…

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Atoms (2)

• There are VAST numbers of atoms in everything.– In just a handful of anything there are about the

same number of atoms as there are grains of sand on all the beaches and deserts on Earth combined

Photo Credit: http://www.morguefile.com ID = 104101

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Let us embark on a temperature excursion…

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Room Temperature

• Let’s start out at room temperature…

Room Temperature

(about 20 C)

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Melting Ice…

• And then get a little bit colder…

Photo credit http://www.cepolina.com/freephoto/

Room Temperature

(about 20 ºC)

Melting Ice

(0 C)

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Melting Ice…

• What happens when an ice cube touches your hand?

Melting Ice…

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Heat Transfer

Hot Object Cold Object

What happens

when they

come closer?

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Heat Transfer

What happens when

a fast moving atom

hits

a slow moving atom?

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Why did you feel cold and wet?

• Water molecules in the ice speed up and escape the electrical attraction of their neighbours

• Causes change of state from solid to liquid

• Atoms and molecules in your hand slow down

• Changes the rate at which special cells to send electrical signals to your brain - interpreted as a ‘too cold’ message

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‘Dry ice’ - Solid Carbon Dioxide

• Jolly chilly…

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A short cold story…

Solid Carbon Dioxide and the balloon

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Liquid nitrogen

• Getting cold…

Room Temperature (about 20 C)Melting Ice

(about 0 C)

Solid CO2

(-79.2 C)

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‘Dry ice’ - Solid Carbon Dioxide

• Carbon dioxide is unusual in that it transforms straight from the solid state to the gaseous state

Balloon

Spoon

Solid CO2 Tie Balloon

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‘Dry ice’ - Solid Carbon Dioxide That’s a million million!

• Stupendous numbers– Molecules travel around 500 metres per second: 1000 miles per hour– Every atom in the surface of the balloon is struck about 1012 times per second

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Did you do your homework?

• The coldest place on Earth?

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The phases of matter…

Solids, liquids and gases

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A word about solids, liquids and gases

• Solids, liquids and gases are called ‘phases’ of matter…

Solid GasLiquidevaporate

Not so normal

melt

evaporatemeltNormal

Solid Gassublimate

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Solids

• A caricature of a solid

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Liquid

• A caricature of a liquid

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Liquid

• A caricature of a gas

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Solids, liquids, and gases

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Liquid nitrogen

• Getting cold…

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Liquid nitrogen

• Getting cold…

Room Temperature (about 20 C)Melting Ice

(about 0 C)

Solid CO2

(-79.2 C)

Liquid Nitrogen (about -196 C)

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Another short cold story…

Liquid Nitrogen and the balloon

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Liquid nitrogen (2)

• At 20 C molecules travel at around• 500 metres per second: 1000 miles per hour

• At -196 C molecules travel at about half this speed:• 250 metres per second: 500 miles an hour

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And its not just balloons…

Magnetism (Part I)

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Liquid nitrogen (4)

The magnetic properties of terbium…

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High Temperature Low Temperature

Liquid nitrogen (3)

Slowing the random motion of the terbium atoms allows a magnetically ordered state to manifest itself

A representation of an atom of terbium

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So what happens if you keep getting colder…?

If the jiggling gets slower and slower then eventually atoms stop jiggling• This corresponds to the lowest conceivable temperature• Absolute zero

Room Temperature (about 20 C)

Melting Ice (0 C)

Solid CO2

(-79.2 C)

Liquid Nitrogen

(-196 C)

Absolute Zero

(-273.15 C)

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Lord Kelvin (William Thompson)

• To measure is to know• If you can not measure it, you can not improve it• Heavier than air flying machines are impossible• Radio has no future• X-rays will prove to be a hoax

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Absolute Temperaturekelvin

• Used by scientists - I won’t mention it again.

Room Temperature (about 295 kelvin)

Melting Ice (273.15 kelvin)

Solid CO2

(193.4 kelvin)

Liquid Nitrogen

(77 kelvin)

Absolute Zero

(0 kelvin)

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And now let’s start getting warm

• Normal body temperature for all mammals is 37 °C…

Temperature ofMammals

(about 37 C)

Room Temperature (about 20 C)Melting Ice

(about 0 C)

Solid CO2

(-79.2 C)

Liquid Nitrogen (about -196 C)

Absolute Zero

(-273.15 C)

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The Body Temperature of Animals

Animal Temperature

(C )

Range

(C )

Horse 38.0 0.5

Dog 38.2 1.0

Cat 38.5 0.7

Whale 37.0 ?

Rat 38.5 0.5

Guinea Pig 38.2 1.0

Photo Credit http://www.graficworld.it/public/photos/cat-dog-19.jpg

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And warmer still…

• Water boils at 100 °C…

Temperature ofMammals

(about 37 C)

Room Temperature (about 20 C)Melting Ice

(about 0 C)

Solid CO2

(-79.2 C)

Liquid Nitrogen (about -196 C)

Absolute Zero

(-273.15 C)

Water boils

100 C

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The Leidenfrost Effect

• Water boils at 100 °C…• When it touches a very hot surface, it turns

immediately to a vapour which causes droplets to float on a bed of vapour.

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Break time Activity

• Go forth, and be amused• Take care. Liquid Nitrogen and solid

CO2 are cold and can give severe frostbite.

• Balloons• Ice Cream• Thermal Camera

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Getting hotter…

Much hotter…

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And how hot is a candle flame?

• Guess!

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And how hot is a gas flame?

• Guess!

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A paperclip nightmare…

Magnetism (Part II)

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Liquid nitrogen (4)

The magnetic properties of iron…

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High Temperature Low Temperature

Liquid nitrogen (3)

Speeding up the random motion of the iron atoms destroys the magnetically ordered state of iron

A representation of an atom of iron

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• Increasing the random motion of the iron atoms destroys the magnetically ordered state

Comparing Iron and Terbium

Room Temperature (about 20 C)

Melting Ice (0 C)

Solid CO2

(-79.2 C)

Liquid Nitrogen

(-196 C)

Absolute Zero

(-273.15 C)

Body Temperature (37 C)

Water Boils (100 C)

Magnetism of Iron destroyed

(780 C)

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• Magnetism is a ‘low’ temperature phenomenon– Even when the low temperature is quite high!

Comparing Iron and Terbium

Magnetism of Terbium destroyed around -100 ºC

Magnetic Non-magnetic

Magnetic Non-magnetic

Terbium

Iron

Magnetism of Iron destroyed around 780 ºC

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• The hottest things in your house are your light bulbs!– They become white hot 2500 °C in a fraction of a second

Getting hotter still…

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• The colour of a star depends upon its surface temperature

Stars…

Picture Credit:Richard Powellhttp://www.atlasoftheuniverse.com/me.html

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Reminder…

And how does this link to last week…

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A word about frequency (1)

• 1 oscillation per second is called 1 hertz

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A word about frequency…

oscillations per second is called a…

1000(a thousand) (103)

kilohertz (kHz)

1000000 (a million) (106)

megahertz (MHz)

1000000000 (a billion) (109)

gigahertz (GHz)

1000000000000 (a trillion) (1012)

terahertz (THz)

1000000000000000 (a million billion) (1015)

petahertz (PHz)

PfB1 101 102 103 104 105 106 107 108 109 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022

Radio & TVInfra Red

Microwaves

Gamma-Rays

X-Rays

Ultra Violet

Frequency (Hertz)

1000 THz (Blue)400 THz (Red)

Electromagnetic spectrum

PfB1 101 102 103 104 105 106 107 108 109 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022

Radio & TVInfra Red

Microwaves

Gamma-Rays

X-Rays

Ultra Violet

Frequency (Hertz)

Electromagnetic spectrum

2200 °C

800 °C

300 °C

20 °C

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Summary

Heat

• Heat is the ceaseless disordered motions of atoms and molecules

• Temperature is a measure of the speed with which atoms and molecules move

• Atoms and molecules are electrical in their nature, and as they move they are constantly emitting and absorbing electromagnetic radiation

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Spectra

• Last week we saw that different sources of light have quite different spectra– Discrete (made of ‘lines’) – Continuous (Like a rainbow)

• We make light by simply ‘hitting’ an atom: hard– Strike it with an other atom – Strike it with an electron– ‘Shake it’ with an electric wave

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Lets remind ourselves about atoms (1)

• The internal structure of atoms

Electrons• ‘orbit’ around the outside of an atom• very light• possess a property called electric charge

Nucleus• occupies the centre• very tiny and very heavy• protons have a property called electric charge• neutrons have no electric charge

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Lets remind ourselves about atoms (2)

• Nuclei (+) attract electrons (-) until the atom as a whole is neutral• The electrons repel each other

– They try to get as far away from each other as they can, a– and as near to the nucleus as they can

Electrons• Electrons possess 1 unit of negative

charge

Nucleus• protons possess 1 unit of positive charge• neutrons have no electric charge

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Visible light…

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Light from atoms…

If an atom or molecule is ‘unconstrained’ then • When it is hit, it ‘rings’ like a bell• Atoms ‘ring’ at their natural frequency: resonance• Each type of atom vibrates in a characteristic manner.

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• If an atom or molecule is ‘constrained’ then it cannot ‘ring’ clearly.

• The light which emerges has a mixture of all possible frequencies• The balance of colours in the spectrum depends on how fast the

atoms are jiggling – i.e. on temperature.

Light from atoms in solids (1)

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Infra Red Light…

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What happens if you knock a molecule?

• If a molecule is hit, the atoms within a molecule vibrate. • Because atoms are thousands of times heavier than electrons

they ‘ring’ with a much lower frequencies.• The light given off is in the infra red range of the spectrum.

H20

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Some molecules vibrating

• Different types of molecular jiggling occur at different frequencies

PfB1 101 102 103 104 105 106 107 108 109 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022

Radio & TVInfra Red

Microwaves

Gamma-Rays

X-Rays

Ultra Violet

Frequency (Hertz)

Electromagnetic spectrum

2200 °C

800 °C

300 °C

20 °C

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Infra-Red light

• Objects at around ambient temperature emit infra-red light with a wavelength of about 0.01 mm. For example:– Our bodies– The Earth

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Infra-Red light

• We can see infra-red light using either– a normal video camera – a special ‘thermal’ camera

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Light from atoms in solids

• The filament of a normal light bulb is heated to about 2500 celsius to make it give off ‘white’ light

• When something is at about 800 celsius: its red hot• When its colder, it gives off only infra-red light. We can’t ‘see’ this

light but we can detect it.

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Summary

Heat

• Heat is the ceaseless disordered motions of atoms and molecules

• Temperature is a measure of the speed with which atoms and molecules move

• Atoms and molecules are electrical in their nature, and as they move they are constantly emitting and absorbing electromagnetic radiation

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How it all fits together…

Electromagnetic waves

Atoms

Heat

Electricity

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How it all fits together…

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Homework?

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Homework

Research:

Please find one fact about global warming

(Write it down on a piece of paper and I’ll collect the facts before the Global Warming session)

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One minute feedback

• Please write down one thing you understood this evening.

• Please write down one thing you didn’t understand.

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On-line Resources

• www.protonsforbreakfast.org –This PowerPoint ™ presentation.–Handouts as a pdf file

• blog.protonsforbreakfast.org –Me going on about things

• links.protonsforbreakfast.org –Links to other sites & resources

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See you next weekto discuss… Global Warming!

Goodnight