Chapters 30, 31Light EmissionLight Quanta

Light Emission Topics

• Excitation

• Emission Spectra

• Incandescence

• Absorption Spectra

• Fluorescence

• Phosphorescence

• Lasers

Chapter 31

Spectral lines

Spectra

Let There Be Light!

Excitation

E =hf h = 6.6 x 10-34 j-s

Lines

Absorption Lines

Absorption Spectra

Incandesance

Fluorescence

Fluorescence

Florescent Lights

Lasers

Clicker Questions

1) Electrons with the greater potential energies with respect to the atomic nucleus are:

A) inner electrons. B) outer electrons. C) both the same, actually

2) Light is emitted when an electron A) makes a transition to a lower energy level.B) is boosted to a higher energy level.C) neither of these

3) Which color of light carries the most energy per photon? A) violet B) red C) blue D) green E) all the same

Clicker Questions

4) Atoms can be excited by A) photon impact.B) electron impact.C) thermal agitation.D) all of theseE) none of these

5) An atom that absorbs a photon of a certain energy can then emit A) only a photon of the same or higher energy. B) only a photon of the same or lower energy.C) a photon of any energy. D) only a photon of that energy.

6) The variety of colors seen in a burning log comes from the variety of A) multi-layered incandescent surfaces.B) absorbing gases between the log and the viewer.C) chemicals in the log.D) electron transitions in various atoms.E) temperatures.

Light Quanta Topics

Chapter 31• Quantization & Planck’s

Constant

• Photoelectric Effect

• Wave-Particle Duality

• Double Slit Experiment

• Electron Diffraction

• Uncertainty Principle

• Complementarity

Quantization & Planck’s Constant

Energy is only given off at the atomic level in discrete increments where E = hf

Photoelectric Effect

Photoelectric Effect

Wave/Particle Duality

Wave/Particle Duality

Lois de Broglie (1924)

If waves (i.e. light) can act as a particle when it interacts with matter, then a particle can act like a wave when traveling through space :

Wavelength = h/momentum , = h/p, h = 6.6 x 10-34 j-s

Uncertainty Principle

px >= h/2

Et >= h/2

Clicker Questions

1) Which of the following photons has the greatest energy? A) blue light B) infrared C) green light D) ultraviolet E) red light

2) In the photoelectric effect, the brighter the illuminating light on a photosensitive surface, the greater the

A) number of ejected electrons. B) velocity of ejected electrons.C) both of these D) neither of these

3) In the photoelectric effect, the greater the frequency of the illuminating light, the greater the

A) number of ejected electrons. B) maximum velocity of ejected electrons.C) both of these D) neither of these

Clicker Questions

4) In the double-slit experiment with electrons, the electrons arrive at the screen in a A) particle-like way with a pattern that is particle-like.

B) wave-like way with a pattern that is wave-like.C) wave-like way with a pattern that is particle-like.D) particle-like way with a pattern that is wave-like.

5) According to the uncertainty principle, the more we know about a particle's momentum, the less we know about its

A) mass.B) location.C) kinetic energy.D) speed.E) none of these

6) Which of the following is not quantized?A) electric chargeB) radiationC) energyD) number of people in a roomE) All are quantized.

Clicker Questions

7) When a clean surface of potassium metal is exposed to blue light, electrons are emitted. If the intensity of the blue light is increased, which of the following will also increase?

A) the number of electrons ejected per secondB) the time lag between the absorption of blue light and the start of emission of the electronsC) the maximum kinetic energy of the ejected electronsD) the threshold frequency of the ejected electronsE) none of these

8) A bullet and a proton have the same momentum. Which has the longer wavelength?

A) the bulletB) the protonC) Both have the same wavelength.