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In Young's double-slit experiment (YDSE), which of the following statements about the wavelength of light used are correct?

1. A larger wavelength of light produces a larger fringe width.
2. The position of the central maximum depends on the wavelength of light used.
3. If white light is used in YDSE, the violet colour forms its first-order maximum closest to the central maximum.
4. The central maxima of all wavelengths coincide at the same point.

Correct answer: A larger wavelength of light produces a larger fringe width.

Solution

Fringe width beta = lambda*D/d, so it increases with lambda. (A) correct. The central maximum (zero path difference) is always at the geometric centre regardless of wavelength. (B) incorrect. For white light, y1 = lambda*D/d; violet has the smallest lambda so its first maximum is closest to the central fringe. (C) correct. Since zero path difference is satisfied by all wavelengths at the centre, the central maxima of all colours coincide. (D) correct. Correct statements: A, C, D.

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