Name: _____________________ Lab: Wed12-3/Thu12-3/Thu3-6
SSN:   _____________________ Date: _____________________


Physics 135bL
Quiz #9
(4pts. each)


1. T/F: When the wave nature of light is taken into consideration, the physics of optics is then called geometric optics.
Answer:
False. It's physical optics, of course.


2. Given the following: 
 nl      yn - yo
----  =  ------
2d        L
Suppose the 2nd dark spot of a double-slit diffraction experiment is observed at a distance of 5 mm from the center of the central bright spot. What is n in the above equation? _________________________________________________
Answer:
Since it's the 2nd DARK spot and a DOUBLE-SLIT, that means n=3


3. Continuing with the experiment from #2 above, suppose the slits are 0.25 mm apart and the screen is placed 1.5 m away. What is the wavelength of the light used?
_________________________________________________
Answer:
Using the eqn. from the previous question gives l = 555.6nm


4. In order to have destructive interference, the two waves must be:
Answer:
B -- out of phase.
  1. in phase.
  2. out of phase.
  3. in a stationary phase.
  4. in a transitionary phase.


5. How does the intensity of light vary with the distance, r? (Hint: see the C&H cartoon below)
_________________________________________________
Answer:
Intensity decreases with the square of the distance, r: I1/I2 = r22/r12