Transcript ASTR_PNE_lightII_V01.docx

The Origin and Nature of Light
The Origin and Nature of Light
• Celebration of Knowledge #2 (aka Exam #2)
is Thursday March 8th in N210
• Tailgate Party (aka exam review) is
Wednesday March 7th in N210 from 4-6pm
• HW #5 – Handed out in class Feb 27th on the topic
of Luminosity Area and Temperature, and Due INCLASS Tuesday March 6th
• HW#6 – Masteringastronomy online homework
The
Origin
and
Nature
of
Light
on Properties of Light and Matter.
Available March 1st , Due March 8th by 10am.
What can we learn by
analyzing starlight?
• A star’s temperature
Find the hottest
star(s), how do
you know ?
Star A
Wavelength
Star C
VIBGYOR
Star D
Energy Output per second
Energy Output per second
Energy Output per second
Star B
VIBGYOR
Star A
Star A
Wavelength
VIBGYOR
Wavelength
Which star is larger Star A or Star D?
Star A
Star D
Energy Output per second
1. Star A
2. Star D
3. Same
VIBGYOR
Wavelength
Try to determine EVERYTHING about
how these four stars compare!! Temp,
Energy output, Color, size (area)…..
Energy
Output
per
second
visible
range
Energy
Output
per
second
visible
range
Object A
Object B
VIBGYOR
Energy
Output
per
second
Wavelength
visible
range
VIBGYOR
Energy
Output
per
second
Wavelength
visible
range
Object C
Object D
VIBGYOR
Wavelength
VIBGYOR
Wavelength
But, where does light actually
come from?
electron
Accelerating charges produce
light – electromagnetic radiation!
An atom
consists of a
small, dense
nucleus
(containing
protons and
neutrons)
surrounded by
electrons
- Model
Proposed by
Niels Bohr
1913
A nucleus is
about 10-15 m
in size and the
first electron
orbits out at
10-10 m from
the center of
the atom – The
size of the
electron orbit is
100,000 times
greater than the
size of the
nucleus
Atoms are mostly empty space
So if a nucleus
the size of an
orange (10
cm) was
located at the
center of the
football field,
where would
the electron
be?
End Zone?
Grandstands?
On Campus?
In Tucson?
If the electron’s
orbit is 100,000
times bigger than
the nucleus then
the electron would
be 10,000 m or
6.21 miles away
from the center of
the Football Field!
Still in Tucson, up in
the foothills shopping
at La Encantada!!
The electron
should be thought
of as a
distribution or
cloud of
probability around
the nucleus that
on-average
behave like a
point particle on a
fixed circular path
Nucleus
Photons (light-waves) are emitted
from an atom when an electron moves
from a higher energy level to a lower
energy level
Nucleus
Photons (light-waves) can also be
absorbed by an atom when an
electron moves from a lower energy
level to a higher energy level
Nucleus
Each chemical element produces its own
unique set of spectral lines when it is
excited
We will study three types of spectra!!!
prism
Hot/Dense Energy Source
Continuous Spectrum
prism
Hot low density cloud of Gas
Emission Line Spectrum
prism
Hot/Dense Energy Source
Cooler low density cloud of Gas
Absorption Line Spectrum
The type of spectrum given off depends
on the objects involved
Law #1 – The excited atoms within a hot dense
object give off light of all colors (wavelengths)
and produce a continuous spectrum -- a complete
rainbow of colors (range of wavelengths) without
any spectral lines.
We will study three types of spectra!!!
Hot/Dense Energy Source
prism
Continuous Spectrum
The type of spectrum given off depends on
the objects involved
Law #2 – The excited atoms within a hot,
cloud of gas give off only particular colors
(wavelengths) of light and produce an
emission line spectrum - a series of bright
spectral lines against a dark background.
We will study three types of spectra!!!
Hot low density cloud of Gas
prism
Emission Line Spectrum
The type of spectrum given off
depends on the objects involved
Law #3 – When the light from a hot dense
object passes through a cool cloud of gas, the
atoms within the cloud can absorb particular
colors (wavelengths) of light and produce a
absorption line spectrum - a series of dark
spectral lines among the colors of the rainbow.
We will study three types of spectra!!!
prism
Hot/Dense Energy Source
Cooler low density cloud of Gas
Absorption Line Spectrum
Tutorial: Types of Spectra – p.41
• Work with a partner!
• Read the instructions and questions carefully.
• Discuss the concepts and your answers with one
another. Take time to understand it now!!!!
• Come to a consensus answer you both agree on.
• If you get stuck or are not sure of your answer, ask
another group.
Tutorial: Light and Atoms – LT Handout
• Work with a partner!
• Read the instructions and questions carefully.
• Discuss the concepts and your answers with one
another. Take time to understand it now!!!!
• Come to a consensus answer you both agree on.
• If you get stuck or are not sure of your answer, ask
another group.
Imagine that you observe the Sun using a
telescope in an orbit high above Earth’s
atmosphere. Which of the following spectra
would you observe by analyzing the sunlight?
1.
2.
3.
4.
dark line absorption spectrum
bright line emission spectrum
continuous spectrum
None of the above
If an electron in an atom moves from
an orbit with an energy of 5 to an
orbit with an energy of 10,
A. a photon of energy 5 is emitted
B. a photon of energy 15 is emitted.
C. a photon of energy 5 is absorbed.
D. a photon of energy 15 is absorbed.
E. None of the above
Which of these would cause a “Violet” or
high energy absorption line?
A.
B.
C.
D.
E. None of the above
Which of these shows the atom emitting the
greatest amount of light?
A
B
e-
ee-
C
E
D
e-
e-
e-
What physical situation makes
this spectrum?
The type of spectrum given off
depends on the objects involved
Law #3 – When the light from a hot dense
object passes through a cool cloud of gas, the
atoms within the cloud can absorb particular
colors (wavelengths) of light and produce a
absorption line spectrum - a series of dark
spectral lines among the colors of the rainbow.
prism
Hot/Dense Energy Source
Cooler low density cloud of Gas
Absorption Line Spectrum
What physical situation does a
star like the sun present?
A hot dense
core surrounded
by a low
density outer
atmosphere
The Sun’s Spectrum
All stars
produce dark
line absorption
spectra
What can we learn by
analyzing starlight?
• A star’s temperature
• A star’s chemical composition
Tutorial: Analyzing Spectra – p. 43
• Work with a partner!
• Read the instructions and questions carefully.
• Discuss the concepts and your answers with one
another. Take time to understand it now!!!!
• Come to a consensus answer you both agree on.
• If you get stuck or are not sure of your answer, ask
another group.
Consider the dark line absorption spectra shown below for
Star X and Star Z. What can you determine about the color of
the two stars? Assume that the left end of each spectrum corresponds to shorter
wavelengths (blue light) and that the right end of each spectrum corresponds with
longer wavelengths (red light).
Star X
Star Z
1. Star X would appear blue and Star Z would
appear red.
2. Star X would appear red and Star Z would
appear blue.
3. Both stars would appear the same color.
4. The color of the stars cannot be determined
from this information.