In an experiment, white light is shone vertically down upon a convex spherical lens that is resting $($curved side down$)$ on a flat piece of glass. Which of the following statements correctly explain why there is there a dark ring at the centre of the resulting interference pattern?

NOTE: More than one of the statements may be correct. To get full marks all correct and no incorrect statements must be selected.

Question $4$Select all that apply:

Destructive interference of two reflected rays occurs

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Destructive interference of the reflected ray and the refracted ray occurs

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Constructive interference of two reflected rays occurs

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The thickness of the air wedge is equal to one$-$half wavelength at that location

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The thickness of the air wedge is negligible at that location

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There is a $180$ degree phase difference $($due to reflection$)$ between the two reflected rays

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CheckQuestion $4$