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Properties of Light. A. B. The Speed of Light. Galileo’s Experiment. c = Round Trip Distance/Total Time. Jupiter. Earth. Ole Roemer (1675). Speed of Light. From Roemer’s Experiment c = Diameter of Orbit/Time Delay Modern Value c = 299,792.458 km/sec. Speed of Light.

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the speed of light

A

B

The Speed of Light

Galileo’s Experiment

c = Round Trip Distance/Total Time

speed of light
Speed of Light
  • From Roemer’s Experiment
    • c = Diameter of Orbit/Time Delay
  • Modern Value
    • c = 299,792.458 km/sec
speed of light5
Speed of Light
  • Absolute constant
  • Nothing travels faster
relative velocities
Relative Velocities
  • Our physical sense of velocities is relative
    • How we measure speed depends on how we are moving and how the object we are measuring in moving

Vrel = 2v

v

v

v

Vrel = 0

v

try it with light
Try it with Light

Sun

½ c

c

Intuition says you get ½ c

Einstein says c

slide8

Try it with Light

Sun

½ c

c

Intuition says you get 1½ c

Einstein says c

nature of light
Nature of Light
  • Particle?
    • Newton
  • Wave?
    • Christian Huygens in Newton’s day
    • Thomas Young (1801)
      • Light can diffract - must be a wave
      • Transverse wave
types of waves
Types of Waves
  • Transverse and Longitudinal
electromagnetic spectrum
Electromagnetic Spectrum

Increasing Wavelength

Visible Light

the visible spectrum

400nm 500nm 600nm 700nm

The Visible Spectrum

Wavelength means

COLOR

frequency
Frequency
  • Number of complete events occurring in a period of time
    • Waves/second
  • Examples
    • Second hand on a clock?
      • 1 cycle/minute = 1/60 cycle/sec
    • US Presidential Electons
      • 1 election/4 years = 1/4 election/year
frequency and period

1

Period =

Frequency

Frequency and Period
photon energy
Photon Energy

E  f

E = hf

properties of light18

Properties of Light

Speed (c)

Nothing travels faster

Absolute constant

Wavelength ()

Gamma rays, X-rays, UV, Visible, IR, Radio

In visible wavelength means color

Frequency (f)

Number of complete waves per second

Energy of a Photon (E)

E = hf

basic spectrograph

Collimating Lens

Imaging Lens

Dispersive Element

Slit

Recording Device

Basic Spectrograph
mercury near horizon
Mercury near Horizon

The atmosphere can act like a prism

continuous spectrum
Continuous Spectrum

Source must be HOT and DENSE

emisson bright line spectrum
Emisson (Bright Line) Spectrum

Source must beHOTandTENUOUS

types of spectra

Continuous

Emission

Absorption

Types of Spectra
hydrogen atoms
Hydrogen Atoms
  • Simplest atom
    • One proton, one electron
  • Most abundant atom
    • 90% of universe is hydrogen
planetary model

e-

Force

p

Planetary Model

Since electron orbits the proton, a force exists.

planetary model29

e-

Acceleration

p

Planetary Model
  • Force implies acceleration
  • Accelerating charges emit light
  • Light carries energy (E = hf)
planetary model30

e-

p

Planetary Model

Electron moves closer to the nucleus since it requires less energy to be there.

planetary model31
Planetary Model
  • But the electron is still accelerating
    • Must still be radiating energy (light)
    • Must move still closer to the nucleus
    • Electron will spiral into and collide with the nucleus (in about 10-8 seconds)

Atoms do not exist!!

bohr s hypotheses
Bohr’s Hypotheses
  • Stable electron orbits exist where the electron does not lose energy.
slide33

Electrons can be here

or here

but not here

p

bohr s hypotheses34
Bohr’s Hypotheses
  • Transitions can occur between orbits so long as the electron ends up with the energy of the new level.
hydrogen

5

4

3

Energy

6563 Å photon

2

Hydrogen

Absorption

hydrogen37

5

4

Energy

3

6563 Å photon

2

Hydrogen

Emission

slide38

Hydrogen Atom

5

4

-e

434 nm

3

2

656 nm

-e

1

-e

+P

486 nm

410 nm

-e

-e

400 nm

700 nm

emission and absorption lines
Emission andAbsorption Lines
  • Lines come from electron transitions
    • Energy change either comes from (absorption) or is given to (emission) photon. E
    • Photon energy  Frequency
      • E = hf
    • Frequency  1/(Wavelength)
      • f = c/l
    • Wavelength means COLOR
hydrogen spectrum

Brackett (Far IR)

Paschen (IR)

4

3

Balmer (VIS)

2

1

Lyman (UV)

Hydrogen Spectrum

Energy

slide41

Aluminum

Argon

Calcium

Carbon

Helium

Hydrogen

Iron

Krypton

Magnesium

Neon

Nitrogen

Oxygen

Sodium

Sulfur

Xenon

emission absorption spectra for any element
Emission & Absorption Spectra for any Element
  • http://jersey.uoregon.edu/vlab/elements/Elements.html