Using monochromatic light, interference fringes are produced on a screen placed a distance D from a pair of slits of separation a. The separation of the fringes is x. Both a and D are now doubled. What is the new fringe separation?
Correct answer: B. x
- A. 2x
- B. x
- C. 3x
- D. 4x
Explanation
For double slits: Wavelength λ = xa / Dwhere x: separation of fringes,a: slit separation / distance between slits,D = distance from slits to screen.So, separation of fringes, x = λD / aWhen both a and D are doubled, the fringe separation x = λD / aThe separation between the fringes denoted by x is directly proportional to distance between the slits and screen and inversely proportional to separation between the two slits. Thus doubling the two quantities would ultimately result in cancellation of each other.
This question appeared on the ETEA MDCAT 2014 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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