Verified Solution • 2025–26 Session moderate

QJEEM17Ph98ca: JEE Main 2017 Physics - Class 12 JEEM17Ph98ca Solution: A single slit of width b is illuminated by a coherent…

A single slit of width b is illuminated by a coherent monochromatic light of wavelength λ. If the second and fourthminima in the diffraction pattern at a distance 1 m from the slit are at 3 cm and 6 cm respectively from the central maximum, what is the width of the central maximum ? (i.e. distance between first minimum on either side of the central maximum)

Multiple Choice Options

  • A 1.5 cm
  • B 3.0 cm
  • C 4.5 cm
  • D 6.0 cm

Step-by-Step Verified Solution

For single slit diffraction, sinθ = nλb

From central maxima the position of nth minima = nλDb

Now when,

n = 2, then x2 = 2λDb = 0.03 . . . .(1)

n = 4, then x4 = 4λDb = 0.06 . . . .(2)

Performing (2) − (1) we get,

x4 − x2 = 2λDb = 0.03

∴ λDb = 0.032

As, width of crntral maximum

= 2λDb

= 2 × 0.032

= 0.03 m

= 3 cm

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