A) 2.5
B) \[5.6\times {{10}^{-10}}\]
C) \[4\times {{10}^{-10}}\]
D) \[4.6\times {{10}^{-10}}\]
Correct Answer: B
Solution :
Key Idea: From Bragg?s law, the condition for the reflection of X-rays from series of atomic layers in a given plane is, \[2d\,\sin \theta =n\lambda \] From key idea, wavelength \[\lambda =\frac{2d\,\sin \theta }{n}\] \[{{\lambda }_{\max }}=\frac{2\,d\,{{(\sin \,\theta )}_{\max }}}{n}\] \[=\frac{2\,d\times 1}{1}\,[\because \,\,{{(\sin \theta )}_{\max }}=1]\] = 2d \[=2\times 2.8\times {{10}^{-10}}\,m\] \[=5.6\times {{10}^{-10}}\,m\] Note: Bragg?s reflection can occur only for wavelength \[\lambda \le 2d\]. Due to this fact, the visible light wavelength cannot be used in diffraction.
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