page 169

These values are now substituted back in to give the equations,

	25.35	[ ( n1 – N1) + ( 0.29) ]
G – GN =	------------
	2
	20.02	[ ( n2 – N2) + ( 0.89) ]
G – GN =	------------
	2
	18.42	[ ( n3 – N3) + ( 0.19) ]
G – GN =	------------
	2

XXXXXXXXXXXXX

given that the values for (n1-N1), (n2-N2), (n3-N3) are small whole numbers, we can now find the values looking for the point of coincidence on the special slide rule. In this example we found,

( n1 – N1) = 2

( n2 – N2) = 2

( n3 – N3) = 3

• The use of this magical slide rule is described below,

This seems to be a special ways to search for actual values when only the fractions are known. The basic procedure is, (assuming the numbers are .45 and .56)

1.pick one of the two values (say .45).

2.start looping from 0.45, 1.45, 2.45, 3.45, etc and find the value that results for the other value. Continue until a match occurs.

35.5.0.2 - Laser Measurements of Relative Distance

• In this application, the movable mirror is attached to some test piece. If it moves towards or away, then the detector will see pulses.

page 170

stationary mirror

moving mirror

laser

beam splitter

measured distance

detector

35.5.0.2.1 - Practice Problems

1.Show that the distance between two interference fringes is related to the change in height by calculating path distances.