Transcript EXAM II REVIEW - University of Maryland: Department of

REMINDERS
• Exam II next Thursday, April 14!
• Practice exam will be posted on website
- Same format as first exam –
Multiple Choice & Short Answer
• Review session (Q & A only)
Tuesday, April 12 @ 7 pm
Location: normal lecture hall in Physics
Discussion Review Plan
1.
2.
3.
4.
5.
6.
Study techniques suggestions
Chapters covered
Main equations to know (partial list!)
Key things to know (partial list!)
Practice discussion questions
Practice multiple choice
Study Techniques
• Take notes on your notes – make
summary sheets
• Make these into flash cards & study (not
just definitions and equations – concepts,
too!) Draw pictures!
• Having these things will make studying for
the final easier
• Think about possible essay questions and
be prepared for them!
Material Covered
• Chapter 5 – Light, interaction with matter,
telescopes
• Chapter 10 – The Sun
• Chapter 11 – Stars – overview / properties
• Chapter 12 – Stellar evolution
• Chapter 13 – Deaths of stars
• Textbook, lecture notes, discussion section
activities!
Equations to Be Familiar With
(may be an incomplete list!)
E photon = hc / λ
T ~ 1 / λ peak
distance = 1 / parallax angle
Brightness or Flux, F ~ L / (distance)2
Luminosity, L ~ R2T4
Key Things to Know:
(definitely an incomplete list!)
• Equations already mentioned
• EM spectrum – order of wavelength
regions
• Types of spectra & how they are formed
• Doppler Effect
• Structure of our SUN
• H fusion – (4 H → 1 He + energy +
neutrinos)
• Spectral types, OBAFGKM
Key Things to Know (continued):
• Binaries – how to get masses, which are
stable?
• HR diagram – be able to draw it and label
• Life cycle of low & high mass stars
• Hydrostatic Equilibrium
• Stellar mass cutoffs – 2M, 8 M, 1.4 M, 3 M
(M is the mass of the Sun)
Practice Questions
The electromagnetic spectrum
Figure 3.5
Identify the following portions of the
Electromagnetic spectrum:
A
B
C
D
E
The electromagnetic spectrum
Figure 3.5
Which end of the spectrum
is more energetic, A or B? Why?
A
B
Light has a DUAL NATURE!
“photon”
&
wave
Energy of photon = hc / λ
If the
Hydrogen
gas cloud is
moving
towards
Earth, the
absorption
line marked
will shift in
which
direction?
An absorption line of Hydrogen measured at rest
A
B
How do light and matter interact?
KNOW THESE DEFINITIONS!
•
•
•
•
Emission
Absorption
Transmission
Reflection or Scattering
Electromagnetic radiation
What does this diagram illustrate?
Figure 3.8
What types of light spectra can we observe?
1. Continuous spectra
2. Absorption spectra
3. Emission spectra
Which is the absorption spectrum?
Which is the continuous spectrum?
Which is the emission spectrum?
How spectra are produced – electron transitions
Which spectrum is coming from the coolest object?
BLUE
Yellow
RED
BLACK
The object producing the yellow spectrum might be
what type of star?
BLUE
Yellow
RED
BLACK
Is the star producing the yellow or red spectrum
hotter? Why?
BLUE
Yellow
RED
BLACK
Which spectrum is coming from the hottest object?
BLUE
Yellow
RED
BLACK
Which star is more luminous?
T = 15,000 K
Radius = 1 unit
T = 15,000 K
Radius = 2 units
Which star is more luminous?
T = 3,000 K
Radius = 1 unit
T = 15,000 K
Radius = 1 unit
REMEMBER!
Luminosity of a star is intrinsic.
Depends on Temperature & Radius.
L~R2T4
Flux changes with distance.
F ~ L / d2
For which stars would we observe a Doppler Shift?
A
B
C
Doppler shift
Figure 3.18
Doppler Effect Summary
Motion toward or away from an observer causes a
shift in the observed wavelength of light:
• blueshift (shorter wavelength) 
motion _______ you
• redshift (longer wavelength)  motion AWAY
from you
• greater shift  greater speed
Doppler Effect Summary
Motion toward or away from an observer causes a
shift in the observed wavelength of light:
• blueshift (shorter wavelength)  motion toward
you
• redshift (longer wavelength) 
motion ______ from you
• greater shift  greater speed
How do telescopes help us learn about the
universe?
• Telescopes collect more light than our eyes
 light-collecting area
• Telescopes can see more detail than our eyes 
angular resolution
• Telescopes/instruments can detect light that is
invisible to our eyes (e.g., infrared, ultraviolet)
Angular Resolution
• The minimum
angular separation
that the telescope
can distinguish.
Are the emission lines located
in the UV part of the spectrum or
the IR part of the spectrum?
Which is the correct explanation for the sun’s shining?
Is it on FIRE?
Is it powered by NUCLEAR ENERGY?
Is it CONTRACTING?
E=
2
mc
- Einstein, 1905
What does Einstein’s famous equation mean?
How can we apply it to the Sun?
The balance of
the inward force
of gravity with
the outward force
of pressure due
to radiation is
referred to as ?
Solar wind
A) Corona
B) Chromosphere
C) Photosphere
D) Core
What
enables
nuclei to
overcome
repulsion
and get
close
enough to
fuse in the
core of a
star?
?
Sun releases energy by fusing
four hydrogen nuclei into what?
What will the next fusion product be?
IN
4 protons
OUT
4He
nucleus
2 positrons
2 gamma rays
2 _______????
Total mass is
0.7% lower
Where does it go?
Why do
sunspots
appear dark
on the
surface of
the sun?
Solar Thermostat
Temperature
Decreases
Fusion Rate (Increases or Decreases)?
Core (compresses or expands)?
Temperature
Restored
Practice Multiple Choice
Questions
A difference between an ultraviolet
photon and a radio photon is that
• A. the energy of the radio photon is
greater
• B. only the radio photon is an
electromagnetic wave
• C. only the ultraviolet photon is an
electromagnetic wave
• D. the energy of the ultraviolet photon is greater
• E. none of the answers are correct
A difference between an ultraviolet
photon and a radio photon is that
• A. the energy of the radio photon is
greater
• B. only the radio photon is an
electromagnetic wave
• C. only the ultraviolet photon is an
electromagnetic wave
• D. the energy of the ultraviolet photon is greater
• E. none of the answers are correct
The speed of a radio wave is
•
•
•
•
•
A.
B.
C.
D.
E.
the speed of sound
slower than the speed of light
slower than the speed of sound
the speed of light
none of the above
The speed of a radio wave is
•
•
•
•
•
A.
B.
C.
D.
E.
the speed of sound
slower than the speed of light
slower than the speed of sound
the speed of light
none of the above
The sun
• A. is composed of ionized gas that is mostly
neon
• B. is composed of molecular gas that is mostly
neon
• C. is composed of ionized gas that is mostly
hydrogen
• D. is composed of molecular gas that is
mostly hydrogen
The sun
• A. is composed of ionized gas that is mostly
neon
• B. is composed of molecular gas that is mostly
neon
• C. is composed of ionized gas that is mostly
hydrogen
• D. is composed of molecular gas that is
mostly hydrogen
The energy source for the sun is
• A. combustion of hydrocarbons
• B. solar flares
• C. nuclear fission, the splitting of two
hydrogen atoms
• D. nuclear fusion, the joining of two
hydrogen atoms
• E. combustion of hydrogen
The energy source for the sun is
• A. combustion of hydrocarbons
• B. solar flares
• C. nuclear fission, the splitting of two
hydrogen atoms
• D. nuclear fusion, the joining of two
hydrogen atoms
• E. combustion of hydrogen
The layer of the sun that emits most of
the light we see is
•
•
•
•
A. the corona
B. the chromosphere
C. the photosphere
D. none of the answers are correct
The layer of the sun that emits most of
the light we see is
•
•
•
•
A. the corona
B. the chromosphere
C. the photosphere
D. none of the answers are correct
Electromagnetic radiation from
astronomical objects can be studied from
the surface of the Earth in which part of
the spectrum?
• A. gamma-rays
• B. x-rays
• C. radio
Electromagnetic radiation from
astronomical objects can be studied from
the surface of the Earth in which part of
the spectrum?
• A. gamma-rays
• B. x-rays
• C. radio
The hotter an object
• A. the brighter it appears at all wavelengths,
• B.
• C.
• D.
• E.
and the longer the wavelength at which it
appears brightest
the shorter the wavelength at which it
appears brightest
The brighter it appears at all wavelengths,
and the shorter the wavelength at which it
appears brightest
the longer the wavelength at which it
appears brightest
the brighter it appears at all wavelengths
The hotter an object
• A. the brighter it appears at all wavelengths,
• B.
• C.
• D.
• E.
and the longer the wavelength at which it
appears brightest
the shorter the wavelength at which it
appears brightest
The brighter it appears at all wavelengths,
and the shorter the wavelength at which it
appears brightest
the longer the wavelength at which it
appears brightest
the brighter it appears at all wavelengths
Heat affects wavelength
Figure 3.6
An object emits an emission line
spectrum. If the object moves towards
an observer,
• A. the observed emission lines shift to
shorter wavelengths
• B. the observed emission lines shift to longer
wavelengths
• C. the emission line spectrum shifts to a
continuous spectrum
• D. the emission line spectrum shifts to
an absorption line spectrum
An object emits an emission line
spectrum. If the object moves towards
an observer,
• A. the observed emission lines shift to
shorter wavelengths
• B. the observed emission lines shift to longer
wavelengths
• C. the emission line spectrum shifts to a
continuous spectrum
• D. the emission line spectrum shifts to
an absorption line spectrum
The hottest part of the solar atmosphere
•
•
•
•
A.
B.
C.
D.
found in sunspots
is the photosphere
is the corona
is the chromosphere
The hottest part of the solar atmosphere
•
•
•
•
A.
B.
C.
D.
found in sunspots
is the photosphere
is the corona
is the chromosphere
Which of the following is ordered by
increasing wavelength?
•
•
•
•
A.
B.
C.
D.
infrared, visible, radio, gamma-ray
visible, infrared, radio, gamma-ray
gamma-ray, visible, infrared, radio
radio, visible, infrared, gamma-ray
Which of the following is ordered by
increasing wavelength?
•
•
•
•
A.
B.
C.
D.
infrared, visible, radio, gamma-ray
visible, infrared, radio, gamma-ray
gamma-ray, visible, infrared, radio
radio, visible, infrared, gamma-ray
An atom is ionized if
•
•
•
•
A.
B.
C.
D.
it has lost a proton
it has lost an electron
it has lost a neutron
it has absorbed a photon
An atom is ionized if
•
•
•
•
A.
B.
C.
D.
it has lost a proton
it has lost an electron
it has lost a neutron
it has absorbed a photon
Sunspots appear darker than the
surrounding photosphere because
• A. they have a carbonaceous
composition
• B. they have an icy composition
• C. they are cooler than their surroundings
• D. they are shadowed from coronal
radiation
Sunspots appear darker than the
surrounding photosphere because
• A. they have a carbonaceous
composition
• B. they have an icy composition
• C. they are cooler than their surroundings
• D. they are shadowed from coronal
radiation
High mass stars have shorter lifetimes
than low mass stars because high mass
stars
• A. have luminosities that are far larger than low
mass stars
• B. have less hydrogen than low mass stars
• C. have less helium than low mass stars
• D. release less energy per nuclear reaction
than low mass stars
High mass stars have shorter lifetimes
than low mass stars because high mass
stars
• A. have luminosities that are far larger than low
mass stars
• B. have less hydrogen than low mass stars
• C. have less helium than low mass stars
• D. release less energy per nuclear reaction
than low mass stars
If the Sun were replaced by a black hole
of the same mass,
• A. a great sucking sound would be heard
• B. the Earth would continue to orbit pretty much
as it does now
• C. the Earth would fall directly towards the
black hole
• D. the Earth would spiral into the black hole
over the next 1000 years
If the Sun were replaced by a black hole
of the same mass,
• A. a great sucking sound would be heard
• B. the Earth would continue to orbit pretty much
as it does now
• C. the Earth would fall directly towards the
black hole
• D. the Earth would spiral into the black hole
over the next 1000 years
The most common stars are
•
•
•
•
•
A.
B.
C.
D.
E.
lower main sequence stars
supergiants
giants
upper main sequence stars
neutron stars
The most common stars are
•
•
•
•
•
A.
B.
C.
D.
E.
lower main sequence stars
supergiants
giants
upper main sequence stars
neutron stars
Main sequence stars
• A. are stars which have no hydrogen or
helium
• B. have nuclear fusion of hydrogen
occurring in their cores
• C. are stars which are mostly made of
hydrogen
• D. are stars found in spiral arms
Main sequence stars
• A. are stars which have no hydrogen or
helium
• B. have nuclear fusion of hydrogen
occurring in their cores
• C. are stars which are mostly made of
hydrogen
• D. are stars found in spiral arms
A planetary nebula is
• A. produced by a supernova explosion
• B. a nebula within which planets are
forming
• C. the expelled outer envelope of a
medium mass star
• D. a cloud of hot gas surrounding a planet
A planetary nebula is
• A. produced by a supernova explosion
• B. a nebula within which planets are
forming
• C. the expelled outer envelope of a
medium mass star
• D. a cloud of hot gas surrounding a planet
The density of a __________ is greater
than the density of a ___________.
•
•
•
•
•
A.
B.
C.
D.
E.
neutron star, black hole
pulsar, neutron star
pulsar, white dwarf
white dwarf, pulsar
white dwarf, black hole
The density of a __________ is greater
than the density of a ___________.
•
•
•
•
•
A.
B.
C.
D.
E.
neutron star, black hole
pulsar, neutron star
pulsar, white dwarf
white dwarf, pulsar
white dwarf, black hole
Which star is more luminous?
T = 3,000 K
Radius = 7 units
T = 12,000 K
Radius = 1 unit