Horace, Thanks! Now I understand the fringe motion. Harry
----- Original Message ----- From: Horace Heffner <hheff...@mtaonline.net> Date: Friday, September 11, 2009 6:54 pm Subject: Re: [Vo]:Michelson-Morley Interferometer experiment finally done correctly? > > On Sep 11, 2009, at 1:29 PM, Harry Veeder wrote: > > > Thanks for this detailed reply. > > Attached is a screen capture from the video. > > The red dashes indicate the location of the laser. > > Also attached is your diagram with a few additions. > > (Hope both images get through vortex) > > > > Positions B and C on the screen capture correspond to the beam > > splitter's > > stages of displacements B and C on your diagram. > > We can assume so here. > > > A on the diagram is the > > stage when the difference in path lengths is momentarily zero. > > > > > > My question is this: > > > > Should the direction of motion of the pattern change whenever the > beam> splitter passes through stage A or will it only change when > it passes > > through stages B and C? > > > The beam splitter reaches maximum sag twice in each rotation, when > the device and laser is on about a 45 degree angle, and the beam > splitter is parallel to the horizon plane. We can thus assume now > the > beam splitter is at maximum sag at locations B and C in the photo > below, however it is important to note that the value of delta D is > > still a *continuous function* of *all positions* of sagging motion > of > the beam splitter. At maximum sag, the motion of the interference > lines is stopped, and then reverses. The beam splitter then begins > its motion over to the other maximum sag position, which is 180 > degrees away. Note that the interference pattern speed of change > has > only to do with the rate of *change* in the difference between the > two paths, and thus of delta D. For half the rotation cycle we can > see that delta D, and thus the difference, is moving in one > direction, the other half delta D moves the other direction. The > interference line motion matches the *change* in delta D, which is > the displacement of the beam splitter. For half the rotation cycle > we > can see that delta D, and thus the difference, is moving in one > direction, the other half it moves the other direction. This > matches > what is on the video. > > The direction of motion of the interference pattern only stops and > changes direction at the maximum sag positions, because these are > the > only points at which delta D changes its direction. When the beam > splitter is at point A, its normal rest position, and vertical with > > respect to the horizon, the speed of the interference pattern > motion > should be at a maximum, regardless of which half cycle it is on. > > Best regards, > > Horace Heffner > http://www.mtaonline.net/~hheffner/ > > >
