Electromagnetic Spectrum Electromagnetic Spectrum and Quantized Energyand Quantized Energy

Why the electron is what it isWhy the electron is what it is

What is a wave?What is a wave?

A wave is a transfer of energy from A wave is a transfer of energy from one point to another via a traveling one point to another via a traveling disturbancedisturbance

A wave is characterized by its A wave is characterized by its wavelength, frequency, and wavelength, frequency, and amplitudeamplitude

Transverse Transverse Waves that travel Waves that travel perpendicular to perpendicular to the direction of the direction of motion motion

                                 

Examples: Light, -Examples: Light, -p wavesp wavesfor earthquakes, for earthquakes, Ocean waves Ocean waves 

Wavelength (Wavelength (λλ))Distance from Distance from successive crest to successive crest to crest or trough to crest or trough to troughtrough

Measured in Measured in metersmeters

FrequencyFrequencyNumber of crests Number of crests passing by per secondpassing by per secondMeasured in Hertz (Hz) Measured in Hertz (Hz) defined to be one defined to be one cycle per seccycle per secEqual to the inverse of Equal to the inverse of the amount of time it the amount of time it takes one wavelength takes one wavelength to pass byto pass by

Wave SpeedWave Speed

Where, v is the speed of the wave (m/s) λ is the wavelength in meters (m) f is the frequency in Hertz (cycle/s)

vf Traveling Waves move through space at a certain speed

Matter / Quantum Waves Matter / Quantum Waves Electrons and other tiny particlesElectrons and other tiny particles show show wave-like properties wave-like properties A particle moving close to the speed of A particle moving close to the speed of light (c) can diffract or bend around the light (c) can diffract or bend around the edges of objectsedges of objectsAlso, particles do exhibit interference Also, particles do exhibit interference which is a wavelike property   which is a wavelike property   Any moving matter has wave Any moving matter has wave characteristics in theory BUT the characteristics in theory BUT the wavelength of any life-size particle, like a wavelength of any life-size particle, like a golf ball, is so small that it is negligiblegolf ball, is so small that it is negligibleTo learn about matter waves in depth go To learn about matter waves in depth go on to the next slide.on to the next slide.

If we can sometimes consider an If we can sometimes consider an electron to be a wave, what is its electron to be a wave, what is its

wavelength?wavelength?

Its wavelength depends on its Its wavelength depends on its momentum momentum

oror

where p is momentum in kg*m/s, h is where p is momentum in kg*m/s, h is Planck’s constant = 6.63 x 10Planck’s constant = 6.63 x 10-34 -34 J, and J, and λλ is the wavelength in metersis the wavelength in meters

h

p

mv

h

What is Planck’s constant?What is Planck’s constant?

Planck’s Constant is the size where Planck’s Constant is the size where quantum mechanics becomes necessaryquantum mechanics becomes necessarySince "Planck's Constant" (‘h’= 6.63 x 10 Since "Planck's Constant" (‘h’= 6.63 x 10 - -

3434 Js) is such a tiny number, quantum Js) is such a tiny number, quantum mechanics is needed only at very small mechanics is needed only at very small scalesscalesAn electron also has spin that is An electron also has spin that is quantizedquantized in units of h. in units of h. These units (Joule-sec) are units of These units (Joule-sec) are units of angular momentum angular momentum

Electromagnetic Waves Electromagnetic Waves

Waves of energy emitted from any accelerating Waves of energy emitted from any accelerating chargeschargesAny object that is above absolute zero emits Any object that is above absolute zero emits electromagnetic waveselectromagnetic wavesThe entire range of possibilities is called the The entire range of possibilities is called the “Electromagnetic Spectrum” “Electromagnetic Spectrum” Still confused? Then click What are Still confused? Then click What are electromagnetic waves? electromagnetic waves? To learn about the wavelength of photons click to To learn about the wavelength of photons click to the next slide. the next slide.

Electromagnetic WavesElectromagnetic Waves

Wavelength is :Wavelength is :

Where, c is the speed of light (3 x 108 m/s in a vacuum)

λ is the wavelength in meters f is the frequency in HertzAnd h is Planck’s constant (there it is again- do you remember its value?)

E is the energy of a photon in Joules

E

hc

f

c

What is this “photon” term you’re What is this “photon” term you’re throwing in there?throwing in there?

A photon is a bundle (quantum) of A photon is a bundle (quantum) of lightlight

A photon has energy equal to A photon has energy equal to

Recall thatRecall that

h is Plank’s constant h is Plank’s constant

νν is the frequency of the radiation is the frequency of the radiation (wave)(wave)

hE

What does a photon do?What does a photon do?Both magnetic and Both magnetic and electric forces electric forces involve the involve the exchange of exchange of photonsphotons

The photon has zero The photon has zero rest mass, but has rest mass, but has momentum, can be momentum, can be deflected gravity, deflected gravity, and can exert a and can exert a forceforce

X-RAYSX-RAYSEmitted when an electron Emitted when an electron moves from certain excited moves from certain excited states back down to its states back down to its ground state, or when an ground state, or when an electron that is moving electron that is moving very quickly is suddenly very quickly is suddenly stopped stopped Two groups - long Two groups - long wavelength (soft x-rays) wavelength (soft x-rays) and shorter wavelength and shorter wavelength (hard x-rays)(hard x-rays)Used for radiography (x-Used for radiography (x-ray photography) and to ray photography) and to look at materials in look at materials in industry for defects industry for defects Sources:  emitted by heavy Sources:  emitted by heavy atoms after bombardment atoms after bombardment by an electronby an electron

ULTRAVIOLETULTRAVIOLETAbove the color violet  Above the color violet  Three groups - UV A, Three groups - UV A, UV B, and UV C. UV B, and UV C. ““A” type: longest A” type: longest wavelength; least wavelength; least harmful harmful UV B and UV C are UV B and UV C are absorbed by DNA in absorbed by DNA in cells cells Used by the body to Used by the body to produce vitamin D, to produce vitamin D, to kill bacteria on kill bacteria on objects, and for sun objects, and for sun tanning tanning Sources:   Ultra hot Sources:   Ultra hot objects 5000°C or objects 5000°C or moremore

VISIBLE LIGHTVISIBLE LIGHTWhite light: White light: combination of combination of all all the colors the colors Rainbow: example Rainbow: example of white light that of white light that has been separated has been separated into a continuous into a continuous spectrum of colorsspectrum of colorsThe names of colors The names of colors are assigned in are assigned in order of their order of their wavelengths wavelengths Used for Used for communicationscommunications

(fiber optics)(fiber optics)Sources:   very hot Sources:   very hot objectsobjects

Color Wavelength interval Frequency interval

red ~ 625 to 740 nm ~ 480 to 405 THz

orange ~ 590 to 625 nm ~ 510 to 480 THz

yellow ~ 565 to 590 nm ~ 530 to 510 THz

green ~ 520 to 565 nm ~ 580 to 530 THz

cyan ~ 500 to 520 nm ~ 600 to 580 THz

blue ~ 430 to 500 nm ~ 700 to 600 THz

violet ~ 380 to 430 nm ~ 790 to 700 THz

INFRAREDINFRARED

Thought of as heat but Thought of as heat but is not alwaysis not alwaysFar infrared energy is Far infrared energy is heat energy. heat energy. All objects that have All objects that have warmth radiate warmth radiate infrared waves infrared waves Easily absorbed and Easily absorbed and re-radiated.  re-radiated.  Used in remote Used in remote controls,  surveillance, controls,  surveillance, therapy of musclestherapy of musclesSources:  Humans, Sources:  Humans, the sunthe sun

MICROWAVESMICROWAVES

1 mm-1 dm in length 1 mm-1 dm in length Absorbed by water Absorbed by water molecules – how molecules – how microwave ovens heat microwave ovens heat foodfoodUsed in Used in telecommunications telecommunications and power and power transmission transmission Sources:  electric Sources:  electric circuits, many stars, circuits, many stars, microwave ovensmicrowave ovens

RADIO WAVESRADIO WAVES10 cm- 100,000+m 10 cm- 100,000+m  in length  in length Only cosmic waves Only cosmic waves the reach the the reach the surface of the Earthsurface of the EarthCause of noiseCause of noiseDivided into smaller Divided into smaller frequency frequency dependent groups dependent groups called bands   called bands   Used Used for communications for communications Sources:  transmitteSources:  transmitters and sparks from rs and sparks from motorsmotors

So What is this Quantum Thing?So What is this Quantum Thing?

A Quantum is the Energy required to A Quantum is the Energy required to jump an Electron from one orbit to jump an Electron from one orbit to another.another.