The path difference 'BD' for destructive interference is:
Correct answer: A. (m + ½) λ
- A. (m + ½) λ
- B. mλ
- C. d sin θ
- D. 3λ
Explanation
Destructive interference occurs when the path difference between two waves is an odd multiple of half wavelengths, expressed as (m + ½)λ, where m is an integer. This causes the waves to cancel out. Option A is correct as it matches this condition. Option B is incorrect since it represents the condition for constructive interference, where waves reinforce each other. Option C is a formula derived from Bragg's Law, used in crystallography, not directly related to interference path differences. Option D is an arbitrary multiple of the wavelength that does not fit the criteria for either type of interference.
This question appeared on the UHS MDCAT 2010 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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