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Chapter 18 - 18.16

16. At the location of the detector, the phase diﬀerence between the wave which traveled straight down the

tube and the other one which took the semi-circular detour is

∆ φ = k ∆ d = 2 π

λ ( πr

−

2 r ) .

For r = r min we have ∆ φ = π , which is the smallest phase diﬀerence for a destructive interference to

occur. Thus

40 . 0cm

2( π

r min =

2) =

2) =17 . 5cm .

2( π

−