Transcript A look into our universe

 How
does the
wavelength of a light
beam and the size of a
slit it is going through
control the amount of
diffraction?
DO
STOP
WORK
 SLC

Expect more e-mails/phone calls if you’re not
showing up
 Physics
Club
 Missing
Lens
 Learn
what spectrometry is and how
scientists use it to identify specific atoms.
 Be
able to calculate the photons released
from different energy level drops.
 Let’s
go over it.
What can electromagnetic waves tell us
about stars, planets, and galaxies?
 Spectroscopy
is the process of obtaining a
spectrum and reading the information it
contains.
 Each
 If
element has its own unique spectra.
we collect the spectra of distant objects in
our universe we can figure out what
elements they are made of.

To perform spectroscopy you need a spectrometer

A spectrometer is an instrument used to measure
properties of light over a specific portion of the
electromagnetic spectrum

For visible light we will use a spectrometer that has a
prism in it and we will use our eyes as the detector.

Different examples of spectrometers
 Two
ways
 1. Draw what you see
 2. Plot an Intensity vs.
Wavelength Graph

Continuous Spectrum


Emission Line Spectrum


Spectrum of an ordinary light bulb; rainbow because
it has all the visible wavelengths in it
A thin cloud of gas emits light only at specific
wavelengths that depend on its composition and
temperature
Absorption Line Spectrum

If a cloud of gas is between us and a white light
source, we still see most of the continuous light
emitted by the light. However, the cloud absorbs
light of specific wavelength and leaves dark lines
1.
What can a spectrometer tell us about a
very distant object?
2.
What are the three types of spectra?
 In
1913 Niels Bohr proposed that an atom has
a positively charged nucleus surrounded by
electrons that travel in circular orbits around
the nucleus – similar to the structure of a
solar system, but with the attraction
provided by electrostatic forces rather than
gravity.
 Bohr
said that when energy is added to an
atom it becomes excited and the electrons
can temporarily move up to higher orbits.
 The
Bohr Model says that as an electron
returns to its normal orbit it releases the
energy it previously absorbed in the form of
a photon.
 When
incoming energy excites a hydrogen
atom, its electron is moved into a higher
energy level.
 Atoms do not want to stay in higher energy
levels
 So as the electron returns to its original
energy level it releases the energy that
originally excited it as a photon (light
particle)

The Bohr model has been superseded by
quantum mechanics.

Electrons do not stay in perfect little orbits, nor
are they held there by the electrostatic force.

Quantum mechanics says that electrons are in
“electron clouds” that show the probability of an
electron being there.
1.
2.
What does an electron do as it absorbs
energy?
What happens when an electron drops an
energy level?
 SLC

Expect more e-mails/phone calls if you’re not
showing up
 Physics
Club
 Missing
Lens
 Learn
what spectrometry is and how
scientists use it to identify specific atoms.
 Be
able to calculate the photons released
from different energy level drops.
A
specific photon is emitted during any
energy level transition as long as the
electron is dropping down at least one
energy level.
 To
figure out the energy between any
transition use:
 This
photon has a specific frequency that
corresponds to the energy released from the
atom
 Remember:
 We
organize energy levels on “Energy Level
Diagrams”
 Emission
and absorption lines form as a
direct consequence of the fact that each
type of atom, ion, or molecule possesses a
unique set of energy levels.
 We
know the energy levels of atoms, ions,
and molecules so we just need to match our
experimental observations with what we
already know.
1electronvolt (eV)
= 1.60x10^-19 J
(Reference Table)
When an atom ionizes it
loses all of its electrons

The negative eV value describes the difference
in energy between an electron in an energy level
and an electron infinitely far from the nucleus

Where



Z is the atomic number
n is the energy level (1, 2, 3,….)
This only works as an approximation for a single
electron (need quantum mechanics)
 What
is the energy of the photon emitted
from a hydrogen atom when the electron
falls from level 3 to 1?
 Is
this different than if it fell from level 3 to
2 and then 2 to 1?
 n=3
to n=1;
 n=3:-1.51eV
 n=1:-13.60eV
𝐸𝑝ℎ𝑜𝑡𝑜𝑛 = −1.51𝑒𝑉 − (−13.60𝑒𝑉)
𝐸𝑝ℎ𝑜𝑡𝑜𝑛 = 12.09𝑒𝑉
 n=3
to n=2
 n=3:-1.51eV
 n=2:-3.40eV
 n=2
to n=1
 n=2:-3.40eV 𝐸
𝑝ℎ𝑜𝑡𝑜𝑛 = −3.40𝑒𝑉 − (−13.60𝑒𝑉)
 n=1:-13.60eV
𝐸𝑝ℎ𝑜𝑡𝑜𝑛 = 10.20𝑒𝑉


What frequencies do the three different photons
have?
𝐸3 𝑡𝑜 1 = ℎ𝑓
1.6𝑥10−19 𝐽
 12.09𝑒𝑉
1𝑒𝑉
 𝑓 = 2.9𝑥1015 𝐻𝑧

= 6.63𝑥10−34 𝐽 ∗ 𝑠(𝑓)
𝐸3 𝑡𝑜 2 = ℎ𝑓
1.6𝑥10−19 𝐽
1𝑒𝑉
14

1.89𝑒𝑉

𝑓 = 4.6𝑥10 𝐻𝑧
= 6.63𝑥10−34 𝐽 ∗ 𝑠(𝑓)

𝐸2 𝑡𝑜 1 = ℎ𝑓
1.6𝑥10−19 𝐽
1𝑒𝑉
15
= 6.63𝑥10−34 𝐽 ∗ 𝑠(𝑓)

10.20𝑒𝑉

𝑓 = 2.4𝑥10 𝐻𝑧

Would we be able to see all three photons with our
eyes?
No, only the photon released from energy level 3 to 2
falls within the visible spectrum of the EM radiation.

 Page
29.
30.
31.
32.
33.
772 answer questions 29, 30, 32, 33
3.91eV; this energy corresponds to level E6
1.91eV
Skip it.
A) 2.72eV B) 3.06eV
1.24eV; 2.99x10^14Hz
 Regents


Part 2
June 2014
Due Friday: Even if you miss class
 Using

a spectrometer with LEDs demo
Why aren’t the colors in very thin circles?
 What
can a spectrometer tell you about how
a fluorescent light works?
 Missing
Lens
 Homework
 No

due Friday
Physics Club today
Tomorrow
 SLC
Thursday
 We
will use 5 samples
 Draw
what you see
 Compare it to a known spectrum
 Record
spectra on a separate sheet of graph
paper. Your scale should range from 400nm
to 700nm.
 Use the whole width of the paper.
450nm
400nm
550nm
500nm
650nm
600nm
700nm