Suppose you are measuring double-slit interference patterns using an optics kit that contains the following options that you can mix and match: a red laser or a green laser, a slit width of 0.04 or 0.08 mm; a slit separation of 0.25 or 0.50 mm. Estimate the minimum distance L you can place a screen from the double slit that will give you an interference pattern on the screen that you can accurately measure using an ordinary 30 cm (12 in) ruler.

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hocelwsmjc · Accepted Answer

The minimum fringe width which can be measured by using the scale 30 cm is 1 cm. Thus, the minimum fringe width is   β  =  1     c  mThe slit separation should be minimum d=0.25 mm.The wavelength for red light is   λ  =  700  ×      10          −      9           m  .The expression for minimum distance is:  L  =            β      d        λ  Substitute all the known values in the above equation.  L  =            (      1             c      m      ×                        1                     m                          100                     c          m                    )      (      0.25             m      m      ×                                    10                          −              3                                           m                          1                     m          m                    )              700      ×              10                  −          9                           m      L=3.6 mThus, the minimum distance is 3.6 m.

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