phys 214. planets and life - engineering physicsphys214/lecture13.pdfphys 214. planets and life dr....
TRANSCRIPT
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Phys 214. Planets and Life
Dr. Cristina Buzea
Department of Physics
Room 259
E-mail: [email protected]
(Please use PHYS214 in e-mail subject)
Lecture 13. Midterm review
February 4th, 2008
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Answers: Quiz 1
1. Astronomy has shown us that the fundamentallaws of physics are
A) the same everywhere in the universeB) the same in our solar system but different
beyond the solar systemC) completely random and unpredictableD) different on other planets in our solar system2. Among the other planets, probably the most
likely place to find evidence for life eithernow or in the past is on
A) VenusB) MercuryC) JupiterD) Mars3. Using current spacecraft, how long would it
take to reach the nearest stars?A) hundreds of thousands of yearsB) millions of yearsC) only a few yearsD) thousands of years4. The study of life in the universe is best
described by the termA) astrochemistryB) bioastronomyC) astrobiologyD) exobiology5. For most of human history it was believed that
Earth was at the center of the universe. Thisidea is referred to as
A) geocentricB) eccentricC) heliocentricD) egocentric
6. The Ptolemaic model has planets moving inA) elliptical orbits about the SunB) a simple circle about the EarthC) a simple circle about the SunD) small circles, the centers of which move in a larger circle
about the Earth7. Stellar parallax is the apparentA) shift in position of nearby stars as the Earth moves
around the SunB) westward motion of a planet with respect to the
background starsC) shift in position of nearby stars as the Sun moves about
the center of the galaxyD) shift in position of nearby stars as the Earth rotates on its
axis8. The astronomical unit (AU) is defined to be equal toA) average distance between the Earth and SunB) average distance between the Sun and the planet PlutoC) distance between the Sun and the nearest starD) diameter of the Earth9. The light-year is defined to be theA) time it takes light to travel from the Sun to the EarthB) time it takes for light to travel from the nearest star to the
EarthC) distance light travels in one yearD) average distance between the Earth and the nearest star10. If we were to detect a signal from an advanced civilization
in 2013 which is located at a distance of 7 light-years fromthe Sun, in what year was the signal actually transmitted?
A) 2007B) 2013C) 2020D) 2006
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Marks - lectures attendance correlation
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Feedback
• Always welcome!
• Comments and suggestions envelope on my door’s office (Rm 259).
• E-mail as well!
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Part A. 25 Multiple Choice Questions
(3 mark each x 25= total 75 marks)
1 minute a question - total 25 minutes for this section
Part B. Choose between 2
Explain a physical law using a figure
(16 marks)
10 minutes on this section
Part C. Choose between 2
Calculations
( 9 marks)
10 minutes on this section
+ 5 minutes to review
• Total Time: 50 minutes
• Total 100 marks (maximum)
• Don’t forget to bring a calculator!
Midterm exam structure
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Midterm exam
On top of the first page don’t forget to
write:
- the number that appears near your name
in the attendance sheet and
- your name and student number.
The number from the attendance sheet
helps me arrange faster your exams
in alphabetical order.
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Part A. Multiple choice questions (3 mark each)
Text boxed with red within the lectures is very important and may appear as aquestion.
• Astronomy has shown us that the fundamental laws of physics are
A) the same everywhere in the universeB) the same in our solar system but different beyond the solar systemC) completely random and unpredictableD) different on other planets in our solar system
If you don’t know the answer to a question, go on, don’t get stuck. Leave it for later,after you finished answering A, B, and C.
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Part A. Questions based on the age of the Universe
FAR:FAR: We see a galaxy 7 We see a galaxy 7
billions light-years away asbillions light-years away as
it was 7 billion years ago,it was 7 billion years ago,
when the Universe was halfwhen the Universe was half
its current age of its current age of 14 billions14 billions
years old.years old.
FARTHERFARTHER: We see a: We see a
galaxy 12 billions light-galaxy 12 billions light-
years away as it was 12years away as it was 12
billion years ago, whenbillion years ago, when
the Universe was about 2the Universe was about 2
billions years old.billions years old.
The limit of our observableThe limit of our observable
universe:universe: Light from nearly Light from nearly
14 billion light-years away14 billion light-years away
shows the universe as itshows the universe as it
looked shortly after the Biglooked shortly after the Big
Bang, before galaxiesBang, before galaxies
existed.existed.
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Part A. Going easy on radiometric dating
Half-life = the time for half the number of radioactive nuclei to decay
Example: How old is a rock that contains equal amounts of potassium-40 andargon-40, is the half life of the parent isotope is 1.25 billion years ?
Answer: the rock is 1.25 billion years old!
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Part A. The electromagnetic spectrum
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Part A. The Solar System
Know the order of the planet in our solar system!
The smallest, the largest planet, etc.
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Part A. Question (3 mark)
Example: What gases escaped from the atmosphere of planet Pluto
according to the figure below?
Answer: carbon dioxide, nitrogen, oxygen, water vapour, ammonia,
methane, helium, hydrogen (all gases)
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Part B. Explain a physical law (16 marks)
Example 1. Example 1. Explain Explain KeplerKepler’’s s second law using the figuresecond law using the figure
below.below.
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Part B. Explain a physical law (16 marks)
Example 1. Example 1. Explain Explain KeplerKepler’’s s second law using the figuresecond law using the figure
below.below.
As a As a planetplanet moves around its moves around its orbitorbit, it , it sweeps out equalsweeps out equal areasareas
in equal timesin equal times ( (KeplerKepler’’s s second law). second law). (4 marks)(4 marks)
Perihelion
(3 mark)
Aphelion
(3 mark)
Ellipse (3 mark)
Planet, Sun (3 mark)
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Part B. Explain a physical law (16 marks)
Example 2: Explain Kepler’s third law, including the equation
and units used to describe it.
More distant planets orbit the Sun at slower average speeds, obeying
the relationship
p2=a3
where p is the planet’s orbital period in years, and a is the average
distance (semimajor axis) from the Sun in astronomical units (AU).
1 AU = Earth’s average distance from the Sun about 149.6 million km
Kepler’s law applies to any orbiting object as long as the following two
conditions are met:
• The object orbits the Sun or another star of exactly the same mass.
• We use units of years for the orbital period and AU for the orbital
distances.
3 mark
4 mark
3 mark
3 mark
3 mark
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Part B. Explain a physical law and equation
• If you have an equation don’t forget to define and explain every term
appearing in the equation!
• Don’t just write the equation!
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Part B. Explain a physical law (16 marks)
Example 3. Explain Newton’s law of gravity using the figure below.
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Part B. Explain a physical law (8 marks)
!
Fg =GM1M2
d2
1) Every mass attracts every other mass through the force called gravity.
2) The strength of the gravitational force is directly proportional to the product of their
masses and decreases with the square of the distance between their centres.
M1 M2
d
M1, M2 - masses of two objects
D - the distance between the two objects
3 mark
3 mark
4 mark
3 mark
3 mark
Example 3. Explain Newton’s law of gravity using the figure below.
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Part B. Explain a concept (16 marks)
Example 4. Explain the concept of stellar parallax using the figure below, and define a
parsec.
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•• Stellar parallax Stellar parallax –– apparent shift in position of nearby stars as apparent shift in position of nearby stars asthe Earth moves around the Sun.the Earth moves around the Sun.
• If the parallax angle is small, the distance to the star isapproximated as
• 1 parsec = distance from a star that has a parallax of 1 arcsecond
!
D =1AU
"
3 mark
3 mark
3 mark
4 mark
3 mark
Example 4. Explain the concept of stellar parallax using the figure below, and define a parsec.
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Part B. Example 5. explain a figure (16 marks)
3 mark
3 mark3 mark
3 mark3 mark
Title - carbon dioxide cycle (1 marks)
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Part C. Calculate and fill in the figure (9 marks)
Example 6: Plot Keppler’s third law for the following planets: Mercury, Venus,
Earth and Mars, knowing they have the following semimajor axis: Mercury =
0.387 AU, Venus 0.723 AU, Earth = 1 AU, Mars = 1.524 AU
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Part C. Calculate and fill in the figure (9 marks)
Example 6. Plot Keppler’s third law for the following planets: Mercury, Venus,
Earth and Mars, knowing they have the following semimajor axis: Mercury =
0.387 AU, Venus 0.723 AU, Earth = 1 AU, Mars = 1.524 AU
(NB - if the semimajor axis are given in other units such as km you have to transform it
first into AU!!)
p, O
rbit
al p
erio
d 2
(yea
rs 2
)
3 mark a, Average distance3 (AU3)
p2=a3
3 mark
3 mark for
calculation of
orbital periods
power 2 and
plotting them
Orbital period Semimajor axis
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Previous problem was similar to Figure 2.9 page 28 from the textbook
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Part C. Calculate (9 marks)
Example 7. The largest asteroid, Ceres, orbits the Sun at an average distance
(semimajor axis) of a = 2.77 AU. What is Ceres orbital period p?
!
p2
= a3
!
p2
= a3
Example 8. A planet is discovered orbiting every three month around astar of the same mass as the Sun. What is the planet average distance a?
!
p = a3
!
= 2.773" 4.6 years
3 mark
3 mark
3 mark
!
a = p23
!
= 0.2523" 0.4 AU
3 mark
3 mark
3 mark
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Part C. Calculate (9 marks)
Example 9: A galaxy is moving away from us with a velocity of49,000 km/s. How far away is the galaxy if the Hubbleconstant is 70 (km/s)/(Mpc)?
(Mpc = megaparsec)
Hubble law:
v=H0d
where v = velocity of expansion, d = distance from us to thegalaxy, H0 - Hubble’s constant.
!
d =v
H0
!
=49,000
70= 700 Mpc
3 mark
3 mark
3 mark
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Part C. Calculate (9 marks)
Example 10: The hydrogen beta line emission of the quasar3c273 is measured on Earth at a wavelength of 565.7 nm,while its wavelength when emitted was = 486.1 nm.Calculate the speed this quasar is moving away from us if thespeed of light is 300,000 km/s.
Doppler shift equation:
v = radial velocity, !" = wavelength shift, " = wavelength for
stationary source, c - speed of light
!
=565.7" 486.1( ) # 300,000
486.1= 49,000 km / s
!
v="# $ c
#
3 mark
3 mark
3 mark
!
"
!
"#
#=v
c
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How to review for this exam in 2 days
• Review the lectures (Lecture 2 – Lecture 12)
• Remember boxed text!
• Remember equations!
• When you don’t understand a concept, go to the textbook!
• Review important physicals laws and concepts.
• Review important figures! (especially the ones containing text and
schematics)
• Textbook should be the second edition of “Life in the Universe”
• The second edition is updated with the latest discoveries in astrobiology.
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Midterm exam
Midterm exam - Wednesday February 6th
Don’t forget to bring a calculator
& to learn the formulae!