Phys 214. Planets and Life - Engineering physicsphys214/Lecture13.pdfPhys 214. Planets and Life Dr. Cristina Buzea Department of Physics Room 259 E-mail: [email protected]

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 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

Marks - lectures attendance correlation

Feedback

• Always welcome!

• Comments and suggestions envelope on my door’s office (Rm 259).

• E-mail as well!

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

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 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.

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.

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!

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. Example 1. Explain Explain KeplerKepler’’s s second law using the figuresecond law using the figure

below.below.


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)


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

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!


Example 3. Explain Newton’s law of gravity using the figure below.


!

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.

Part B. Explain a concept (16 marks)

Example 4. Explain the concept of stellar parallax using the figure below, and define a

parsec.

•• 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.

Part B. Example 5. explain a figure (16 marks)

3 mark

3 mark3 mark

3 mark3 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, 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

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

= 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


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


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

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.

Midterm exam

Midterm exam - Wednesday February 6th

Don’t forget to bring a calculator

& to learn the formulae!

Documents

Phys 214. Planets and Life - Engineering physicsphys214/Lecture13.pdfPhys 214. Planets and Life Dr. Cristina Buzea Department of Physics Room 259 E-mail: [email protected]