Question

If a strong diffraction peak is observed when electrons are incident at an angle 'i' from the normal to the crystal planes with distance 'd' between them (see figure). de-Broglie wavelength ${\lambda }_{dB}$ of electrons can be calculated by the relationship (n is an integer)

• A. $dsini=n{\lambda }_{dB}$
• B. $dcosi=n{\lambda }_{dB}$
• C. $2dsini=n{\lambda }_{dB}$
• D. $2dcosi=n{\lambda }_{dB}$

Answer 1

The correct option is D $2dcosi=n{\lambda }_{dB}$

From Bragg's law, $2d\sin \theta =n{\lambda }_{dB}$

or $2d\sin (90-i)=n{\lambda }_{dB}$

or $2d\cos i=n{\lambda }_{dB}$

So option D is correct.