Transcript 3 mark - Department of Physics, Engineering Physics & Astronomy

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
Answers: Quiz 1
1. Astronomy has shown us that the fundamental
laws of physics are
A) the same everywhere in the universe
B) the same in our solar system but different
beyond the solar system
C) completely random and unpredictable
D) different on other planets in our solar system
2. Among the other planets, probably the most
likely place to find evidence for life either
now or in the past is on
A) Venus
B) Mercury
C) Jupiter
D) Mars
3. Using current spacecraft, how long would it
take to reach the nearest stars?
A) hundreds of thousands of years
B) millions of years
C) only a few years
D) thousands of years
4. The study of life in the universe is best
described by the term
A) astrochemistry
B) bioastronomy
C) astrobiology
D) exobiology
5. For most of human history it was believed that
Earth was at the center of the universe. This
idea is referred to as
A) geocentric
B) eccentric
C) heliocentric
D) egocentric
6. The Ptolemaic model has planets moving in
A) elliptical orbits about the Sun
B) a simple circle about the Earth
C) a simple circle about the Sun
D) small circles, the centers of which move in a larger circle
about the Earth
7. Stellar parallax is the apparent
A) shift in position of nearby stars as the Earth moves around
the Sun
B) westward motion of a planet with respect to the
background stars
C) shift in position of nearby stars as the Sun moves about
the center of the galaxy
D) shift in position of nearby stars as the Earth rotates on its
axis
8. The astronomical unit (AU) is defined to be equal to
A) average distance between the Earth and Sun
B) average distance between the Sun and the planet Pluto
C) distance between the Sun and the nearest star
D) diameter of the Earth
9. The light-year is defined to be the
A) time it takes light to travel from the Sun to the Earth
B) time it takes for light to travel from the nearest star to the
Earth
C) distance light travels in one year
D) average distance between the Earth and the nearest star
10. If we were to detect a signal from an advanced civilization
in 2013 which is located at a distance of 7 light-years from
the Sun, in what year was the signal actually transmitted?
A) 2007
B) 2013
C) 2020
D) 2006
Marks - lectures attendance correlation
Feedback
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Always welcome!
Comments and suggestions envelope on my door’s office (Rm 259).
E-mail as well!
Midterm exam structure
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
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Total Time: 50 minutes
Total 100 marks (maximum)
Don’t forget to bring a calculator!
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.
Part A. Multiple choice questions (3 mark each)
Text boxed with red within the lectures is very important and may appear as a
question.
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Astronomy has shown us that the fundamental laws of physics are
A)
B)
C)
D)
the same everywhere in the universe
the same in our solar system but different beyond the solar system
completely random and unpredictable
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.
Part A. Questions based on the age of the Universe
FAR: We see a galaxy 7
billions light-years away as
it was 7 billion years ago,
when the Universe was half
its current age of 14 billions
years old.
FARTHER: We see a
galaxy 12 billions lightyears away as it was 12
billion years ago, when the
Universe was about 2
billions years old.
The limit of our observable
universe: Light from nearly
14 billion light-years away
shows the universe as it
looked shortly after the Big
Bang, before galaxies existed.
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 and
argon-40, is the half life of the parent isotope is 1.25 billion years ?
Answer: the rock is 1.25 billion years old!
Part A. The electromagnetic spectrum
Part A. The Solar System
Know the order of the planet in our solar system!
The smallest, the largest planet, etc.
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)
Part B. Explain a physical law (16 marks)
Example 1. Explain Kepler’s second law using the figure
below.
Part B. Explain a physical law (16 marks)
Example 1. Explain Kepler’s second law using the figure
below.
As a planet moves around its orbit, it sweeps out equal areas
in equal times (Kepler’s second law). (4 marks)
Planet, Sun (3 mark)
Perihelion
(3 mark)
Aphelion
(3 mark)
Ellipse (3 mark)
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
3 mark
p2=a3
4 mark
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).
3 mark
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
3 mark
Part B. Explain a physical law and equation
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If you have an equation don’t forget to define and explain every term
appearing in the equation!
•
Don’t just write the equation!
Part B. Explain a physical law (16 marks)
Example 3. Explain Newton’s law of gravity using the figure below.
Part B. Explain a physical law (8 marks)
Example 3. Explain Newton’s law of gravity using the figure below.
M1
M2
3 mark
d
M1, M2 - masses of two objects
D - the distance between the two objects
MM
Fg  G 1 2 2
d
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.
3 mark
4 mark
3 mark
3 mark
Part B. Explain a concept (16 marks)
Example 4. Explain the concept of stellar parallax using the figure below, and define a
parsec.
Example 4. Explain the concept of stellar parallax using the figure below, and define a parsec.
3 mark
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Stellar parallax – apparent shift in position of nearby stars as
the Earth moves around the Sun.
3 mark
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If the parallax angle is small, the distance to the star is
approximated as
3 mark
1AU
4 mark
D
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
1 parsec = distance from a star that has a parallax of 1 arc
second

3 mark
Part B. Example 5. explain a figure (16 marks)
3 mark
3 mark
3 mark
3 mark
3 mark
Title - carbon dioxide cycle (1 marks)
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
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, Orbital period 2 (years 2)
Orbital period Semimajor axis
3 mark
p2=a3
3 mark
3 mark for
calculation of
orbital periods
power 2 and
plotting them
a, Average distance3 (AU3)
Previous problem was similar to Figure 2.9 page 28 from the textbook
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  a 3
3 mark
p  a3
3 mark
 2.77 3  4.6 years
3 mark
 is discovered orbiting every three month around a
Example 8. A planet
star of the same mass as the Sun. What is the planet average distance a?


2 3
p a
3 mark
a  3 p2
3 mark
3
 0.25 2  0.4 AU
3 mark
Part C. Calculate (9 marks)
Example 9: A galaxy is moving away from us with a velocity of
49,000 km/s. How far away is the galaxy if the Hubble
constant is 70 (km/s)/(Mpc)?
(Mpc = megaparsec)
Hubble law:
v=H0d
where v = velocity of expansion, d = distance from us to the
galaxy, H0 - Hubble’s constant.
d


v
H0
49, 000
 700 Mpc
70
3 mark
3 mark
3 mark
Part C. Calculate (9 marks)
Example 10: The hydrogen beta line emission of the quasar
3c273 is measured on Earth at a wavelength of 565.7 nm,
while its wavelength when emitted was l = 486.1 nm.
Calculate the speed this quasar is moving away from us if the
speed of light is 300,000 km/s.
Doppler shift equation:
Dl  v

l c
v = radial velocity, Dl= wavelength shift, l = wavelength for
stationary source, c - speed of light

v


Dl  c
3 mark
3 mark
l
565.7  486.1  300,000  49,000 km / s
486.1
3 mark
How to review for this exam in 2 days
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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)
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Textbook should be the second edition of “Life in the Universe”
The second edition is updated with the latest discoveries in astrobiology.
Midterm exam
Midterm exam - Wednesday February 6th
Don’t forget to bring a calculator
& to learn the formulae!