Homework Assignment #3
Main topics: Light, Stars
This assignment is due at the beginning of class on Friday, February 28. Late homework will not be accepted.
Homework should be written on paper. Please copy the problem statement onto the page above your solution. Remember to put your name at the top of the page. If you require more than one page, multiple pages must be stapled together. I will take off three points if you do not staple the homework. The homework will be returned once it has been graded in the boxes on the ninth floor of the Physics building, opposite the elevator.
Problems involve either a calculation, or a short answer. Where a calculation is called for, show your work. Where a short answer is called for, a few sentences is sufficient. In either case, be sure to make your reasoning clear, and draw diagrams if that helps you explain your answer.
How many radio photons (assume a wavelength of 1m) does it take to equal the energy of a single ultraviolet photon (assume a wavelength of 100nm, remembering that one nanometer (nm) is 10-9m).
Consider two stars, one of spectral type B and one of spectral type K. The B-star has four times the luminosity, but is twice as far away as the K-star. An astronomer observes these two stars through two filters, one centered 5000 Angstroms, the other centered around 6500 Angstroms.
- (a) What can you say about the ratio of the flux of the B-star to the flux of the K-star as observed through the 5000 Angstrom filter? (I.e. is it greater than one, equal to one, or less than one.)
- (b) What can you say about the ratio of the flux of the B-star to the flux of the K-star as observed through the 6500 Angstrom filter?
Hint: you may find Figure 4.9 in the book helpful. Recall that an Angstrom is 10-10 meters, and that a micrometer (the units on the horizontal axis of the lower part of that figure) is 10-6 meters.
Chapter 12, Question 5 in the text.
Chapter 12, Question 15 in the text.
Chapter 13, Questions 11 and 12 in the text (do both).
Consider a two large clouds of gas with solar abundances (i.e. mostly Hydrogen and Helium, with just a little bit of other things mixed in). Take one cloud of this gas, and make sun-like stars out of it. Let the sun-like stars live their main sequence lifetimes, and then (somehow, magically) disperse those sun like stars back into a cloud of gas. Qualitatively, how will the relative elemental abundances in the cloud which was processed through sun-like stars compare to the cloud which just remained a large, quiet cloud of gas?