PH2400 Exam I answers - Spring 2001

1. d      2. b      3. a      4. d      5. e     

6. See Figure 38.11 in text. With both slits see interference fringes (brownish line) and with one covered see only the "envelope" (blue).
7. The wavelength is too long compared to the atomic spacing.
8. y(x,t) = 0.37 sin(7(x+vt)) e^-(x+vt)2/100
9. They are incoherent. Need coherent sources to see interference.
10. 1/2 I₀ [cos(theta)]^2(N-1)
Bonus: should get 1/2 I₀

11. Amp = 0.23 m Wavelength = 3.7 m Wave speed = 19 m/s
Frequency = 5.1 Hz Traveling toward -x
12. 263 Hz
13. 167 nm
14. 9.47 mm
15. 0.996 Hz and 1.99 Hz