The centre of Newton rings is dark due to:
Correct answer: B. Destructive interference.
- A. Polarization
- B. Destructive interference.
- C. Constructive interference.
- D. Reflection.
Explanation
During constructive interference the path difference between the concave lens and the reflective surface i.e. glass slab must be an odd multiple of λ/2, [2n-1×(λ/2)], where n=natural numbers, for destructive interference it must be an even multiple of λ/2, the centre point of newton rings is formed at the point of contact between the lens and the glass. Since the path difference is zero, the condition of destructive interference is satisfied and the centre point is dark.
This question appeared on the UHS MDCAT 2008 paper, which you can sit online with every answer explained.
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About Superposition and Interference
Superposition states that overlapping waves produce a resultant displacement equal to the algebraic sum of their individual displacements. Interference covers constructive and destructive interference, phase difference, path difference, coherent sources, and conditions for maxima and minima. It differs from diffraction, which involves spreading around openings or obstacles.
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