Homework Assignment #7
This assignment is due at the beginning of class on Friday, October 31. Late homework will not be accepted, including homework turned in at the end of class. If you can't make it to the beginning of class, make sure to turn your homework in to me beforehand.
You must do the first three problems. Each of those problems will be worth 10 points. If you make a sincere, honest effort to answer each question, you will receive at least 5 points of credit.
Staple your homework! If you require more than one page to complete the homework, fasten the multiple pages together with a staple; folding the corner won't cut it. If your homework has multiple pages but you fail to staple, you will be docked 3 points.
The last two problems are given to you as additional review problems. You do not need to turn them in, and they will not be graded when you do. However, solutions to them will be posted along with the solutions to the first three problems. You may want to do them if you think you need extra review in the class.
Please write out the problem statement at the top of your solution. (This is for two reasons; it is so I can know which problem you answered, and that you answered the right problem from the book. It also will make your graded homework more useful as a study aid later.)
Chapter 12, Question 5 in the text (page 326-327).
Look at the H-R diagram on the lower-left corner of Page 325 in your text. Consider a main-sequence star which is 10 times as massive as the Sun.
- (a)Would this star be bluer or redder than the Sun? Why?
- (b)Look up the temperature and luminosity of this star on the H-R diagram. Calculate the radius of the star (in units of Solar Radii) (this is the same as the ratio of this star's radius to the Sun's radius). Now estimate the star's radius based on where it falls between the diagonal constant-radius lines on the diagram. How do your two values compare?
- (c)Suppose this star is one of the faintest ones you can regularly see in lab– about 1012 (one trillion) times fainter than the Sun. How far away is this star?
Again consider the 10 solar-mass star of the previous problem. Assume that the amount of fuel available for producing energy is proportional to the mass of the star– that is, a star that is twice as massive has twice as much fuel to burn, and thus can produce twice as much energy over its lifetime. Given the relative mass of this star to the Sun, and the relative luminosity of this star and the Sun, how long will this star be able to shine? (The Sun will shine for about 10 billion years.)
(The problems below will not be graded, and need not be turned in.)
Chapter 12, Question 14 (page 327).
Chapter 12, Question 16 (page 327).