Constants v Part A A very thin sheet of plastic (71, = 1.57) covers one slit of a double-slit apparatus illuminated by What is the (minimum)

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Constants v Part AA very thin sheet of plastic (71, = 1.57) covers one slit of a double-slit apparatus illuminated by What is the (minimum) thickness of the plastic?680 nm light. The center point on the screen, _ _ _ _ _ _ _instead of being a maximum, is dark. Express your answer to two Significant figures and include the appropriate units.