Read the following :
(A) The width of central band in diffraction pattern.
(B) The width of first bright band in diffraction pattern.
(C) The width of central band in diffraction pattern if D is doubled
(D) The width of first bright band in diffraction pattern if D is tripled
Choose the correct answer from the options given below in increasing order of width.
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (B), (A), (D), (C)
In single-slit diffraction (slit width \( a \), screen at distance \( D \)), the central maximum is twice as wide as each secondary bright band.
\( \text{central band: } 2\lambda D/a \)
\( \text{first bright band: } \lambda D/a \)
Write every width in units of \( \lambda D/a \):
(A) The width of central band in diffraction pattern — \( 2\lambda D/a \)
(B) The width of first bright band in diffraction pattern — \( \lambda D/a \)
(C) The width of central band in diffraction pattern if D is doubled — \( 2\lambda(2D)/a = 4\lambda D/a \)
(D) The width of first bright band in diffraction pattern if D is tripled — \( \lambda(3D)/a = 3\lambda D/a \)
\( (B) \lt (A) \lt (D) \lt (C) \)
The increasing order is (B), (A), (D), (C).