Assignment 2: The Interaction of Light and Matter (Due: 11:00 am, 24 March 2015)

Important Instructions: A. Define every symbol you introduce, unless they are common symbols or as defined in the question.

If you are not sure whether they are common symbols, define it! B. Lay out each step clearly and logically. Points will be deducted if you skip or do not clearly explain

chains of logic, even if you arrive at the correct answer. C. The total mark is 140. 1. [10 marks] From the information provided in the lecture notes, show that the Cosmic Microwave Background

(CMB) originates from a redshift of z ≈ 1100. 2. [10 marks]

3. [5 marks]

4. [5 marks]

5. [20 marks]

6. [10 marks]

7. [10 marks]

8. [10 marks] The fact that we can see stars and galaxies indicates that the interstellar medium is almost completely transparent at optical wavelengths (along lines of sight away from the Galactic plane). Explain why this implies that the bulk of hydrogen atoms cannot be at the n = 3 or higher levels. Do you also expect the interstellar medium to be transparent in the ultraviolet? Provide explanations for your answer. 8. [10 marks]

9. [20 marks]

To answer the last question, you will need to read Chapter 16.3 (and preferably also Chapters 16.1 and 16.2) for context. 10. [10 marks]

11. [10 marks]

12. [10 marks]