Modern Physics Exam 2

Deadline: Friday Dec. 16 at 5:00 pm

Instructions: Answer all questions and submit your answers electronically like the homework. Remember, showing intermediate steps and explaining your reasoning will maximize your partial credit in the case of incorrect answers. You can use any references you like but you must work alone and you are not to consult anyone. Feel free to contact me if you need any clarification on a question.

1. a) Rutherford’s model of the atom is commonly called the Planetary Model, in analogy to our Solar System. Using the appropriate equations, carefully show that at the time this was a very reasonable analogy. (Hint: Consider the forces responsible for uniform circular motion in each system)

b) Explain why physically the Planetary Model cannot represent real atoms which are stable.

2. Bohr postulated the correspondence principle to reconcile quantum theory with classical theory. To what other theory, besides quantum theory, could a correspondence principle be applied? Give an example of this application.

3. Carefully explain how our modern understanding of the atom allows us to determine the composition of distant stars. List 5 elements that have been observed in the Sun.

4. Chapter 4, problem 6.

5. Calculate the wavelengths of the first three lines in each of the Lyman and Paschen series for hydrogen.

6. An electron and a proton are accelerated from rest through the same potential difference. Which particle has the longer wavelength? Justify your answer.

7. If matter has a wave nature, why is this wavelike character not observable in our daily experiences? Justify your answer with a numerical example.

8. Chapter 5, problem 6.

9. Chapter 5, problem 20.

10. Chapter 5, problem 24. (Hint: In order to make certain estimates in part b, you can use your answer to part a as the value of the momentum for any equations you might need in part b)

11. Chapter 6, question 6.

12. Chapter 6, problem 2.