Title: Electromagnetic%20Radiation
1- BUSINESS
- EXAM 2 THURSDAY NOVEMBER 4, 2010
- MATERIAL COVERED CHAPTERS 4, 5 6
- TIME 700PM-800PM
- WHERE (TO BE ANNOUNCED LATER)
- WHAT TO BRING CALCULATOR, ONE PAGE OWN
NOTES - CONFLICT IN SCHEDULE? CONTACT ME TO MAKE SEPARATE
TIME
2Chapter 6 Electromagnetic Radiation
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5Short wavelength --gt high frequency high
energy
- Long wavelength --gt
- small frequency
- low energy
6The electromagnetic spectrum.
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8Which has the longest wavelength?
- Infrared
- Ultraviolet
- X-rays
- Radio waves
9- Rank the following in order of increasing
frequency -
- microwaves
- radiowaves
- X-rays
- blue light
- red light
- UV light
- IR light
10- Waves have a frequency
- Use the Greek letter nu, ?, for frequency, and
units are cycles per sec - All radiation ? ? c
- c velocity of light 3.00 x 108 m/sec
- Long wavelength ?small frequency
- Short wavelength ?high frequency
11The Wave Nature of Light
- The product of the frequency, n (waves/sec) and
the wavelength, l (m/wave) would give the speed
of the wave in m/s.
- So, given the frequency of light, its wavelength
can be calculated, or vice versa.
12The Wave Nature of Light
- What is the wavelength of yellow light with a
frequency of 5.09 x 1014 s-1? (Note s-1,
commonly referred to as Hertz (Hz) is defined as
cycles or waves per second.)
13The Wave Nature of Light
- What is the frequency of violet light with a
wavelength of 408 nm?
14- What is the wavelength of WONY?
- What is the wavelength of cell phone radiation?
Frequency 850 MHz - What is the wavelength of a microwave oven?
Frequency 2.45 GHz
15The Photoelectric Effect
Light can cause ejection of e- from a metal
surface.
An anode () attracts e- Current is measured
16The Photoelectric Effect
- Einstein proposed that light
- is quantized.
- behaves like a stream of massless particles.
- G. N. Lewis later named them photons.
- Imagine photons (balls) hitting e- embedded in
glue. - If the E of the ball
- is low, it cant eject an e-.
- exceeds the strength of the glue, an e- is
released
Higher intensity more photons (balls). If E gt
threshold, more balls eject more e-.
17Quantization of Energy
Light acts as if it consists of particles called
PHOTONS, with discrete energy.
- Energy of radiation is proportional to frequency
E h ?
h Plancks constant 6.6262 x 10-34 Js
18E h ?
Relationships
19Short wavelength light has
- High frequency and low energy
- High frequency and high energy
- Low frequency and low energy
- Low frequency and high energy
20- Rank the following in order of increasing photon
energy -
- microwaves
- radiowaves
- X-rays
- blue light
- red light
- UV light
- IR light
21Energy of Radiation
- What is the frequency of UV light with a
wavelength of 230 nm? - What is the energy of 1 photon of UV light with
wavelength 230 nm?
22What is the energy of a photon of 525 nm light?
- 3.79 x 10-19 J
- 4.83 x 10-22 J
- 3.67 x 1020 J
- 8.43 x 1023 J
23Radio Wave Energy
- What is the energy of a photon corresponding to
radio waves of frequency 1.255 x 10 6 s-1?
24- What is the energy of a mole of 230 nm photons?
- Can this light break C-C bonds with an energy of
346 kJ/mol?
25- Does 1200 nm light have enough energy to break
C-C bonds?
26Where does light come from?
- Excited solids emit a continuous spectrum of
light - Excited gas-phase atoms emit only specific
wavelengths of light (lines)
27Light emitted by solids
28Light emitted by hydrogen gas
29The Bohr Model of Hydrogen Atom
- Light absorbed or emitted is from electrons
moving between energy levels - Only certain energies are observed
- Therefore, only certain energy levels exist
- This is the Quanitization of energy levels
30Emission spectra of gaseous atoms
- Excited atoms emit light of only certain
wavelengths - The wavelengths of emitted light depend on the
element.
31Line spectra of atoms
32Energy Adsorption/Emission
33- For H, the energy levels correspond to
Constant 2.18 x 10-18 J
Energy level diagram
34Each line corresponds to a transition
35Explanation of line spectra
Balmer series
36Bohr Model of the Hydrogen Atom
- Heated solid objects emit continuous spectra.
- Excited atomic gases emit line spectra.
- Each element has a unique pattern.
37Bohr Model of the Hydrogen Atom
- Bohr (1913). The hydrogen e-
Niels Bohr
- Orbits the nucleus.
- Different orbits are possible with different
quantized E values
Rydberg constant 2.179 x 10-18 J
If the e- has n 1 (lowest, most negative E),
the atom is in its ground state. If ionized (e-
removed), n ? (E 0).
38Bohr Model of the Hydrogen Atom
absorption ?E gt 0, n ?
emission ?E lt 0, n ?
Bohrs model exactly predicts the H-atom spectrum.
39Bohr Model of the Hydrogen Atom
Example Calculate the energy and wavelength (in
nm) for an H-atom n 4 ? n 2 transition.
40Bohr Model of the Hydrogen Atom
Calculate E and wavelength (nm) for an H-atom n
4 ? n 2 transition.