1. The Miller indices h, k, and l of parallel planes in a BCC lattice should satisfy which of the following X-ray diffraction reflection rules?
a) h + k + l should be even
b) h, k, and l should all be either even or odd
c) h, k, and l should form Pythagoras triplet
d) all planes allow reflections
Explanation: If the sum of Miller indices becomes odd for a BCC lattice, destructive interference occurs.
2. Minimum interplanar spacing required for Bragg’s diffraction is:
a) λ/4
b) λ/2
c) λ
d) 2λ
Explanation: Maximum value of incident angle can be 90° for which sine is 1. Hence d = λ/2 ( nλ = 2.d.sinθ)
3. Laue’s model pictures XRD as reflection from parallel crystalline planes. Reflection is different from refraction as:
a) diffraction occurs throughout the bulk
b) intensity of diffracted beams is less
c) diffraction in crystals occurs only at Bragg’s angles
d) all of the mentioned
Explanation: Reflection is a surface phenomenon, and large portions of the incident waves can be reflected. Moreover, reflection can occur at any angle of incidence whereas diffraction patterns (alternative dark and bright bands) occur only at Bragg’s angles.
4. In Bragg’s equation [nλ = 2.d.sinθ], θ is the angle between:
a) specimen surface and incident rays
b) normal to specimen surface and incident rays
c) parallel lattice surfaces d distance apart and incident rays
d) normal to parallel lattice surfaces d distance apart and incident rays
Explanation: parallel lattice surfaces d distance apart and incident rays
5. In the powder method of XRD, the intensities of various bright lines are compared to determine the crystal structure. For simple cubic lattice the ratio of intensities at first two maxima are:
a) 1⁄2
b) 3⁄4
c) 1⁄2
d) None of the mentioned
Explanation: For simple cubic lattice, the intensities at subsequent maxima are in the ratio 1:2:3:4:5:6:8
6. K-alpha x-rays have shorter wavelengths than K-beta x-rays?
a) True
b) False
Explanation: K-alpha is formed from a transfer of electrons from L shell to K while K-beta result from M-to-K transition. Hence K-alpha lines have lower energy (or longer wavelength).
7. Frenkel defect belongs to which of the following classes?
a) Point defect
b) Linear dislocation
c) Interfacial defect
d) Bulk defect
Explanation: Frenkel defect occurs when some of the smaller ions shift from their lattice point to interstitial positions.
8. The ratio of the number of vacancies to a total number of lattice points for a metal near melting temperature is of the order of 10-4. For lower temperatures, the ratio:
a) increases
b) decreases
c) remains the same
d) may increase or decrease depending on the metal
Explanation: At lower temperature, less energy is available in the system which means less number of atoms are able to leave their lattice sites to create vacancies.
9. Foreign species is present in which of the following defects?
a) Interstitial
b) Vacancy
c) Substitution
d) All of the mentioned
Explanation: In substitution defect, particles of other species having similar sizes replace the host particles in a lattice whereas interstitial defect occurs when particles of the same species are present at interstitial voids.
10. Edge dislocation and screw dislocation are linear crystalline defects.
a) True
b) False
Explanation: Edge dislocation and screw dislocations are linear crystalline defects or line defects.