# Engineering Physics Questions and Answers – Bragg’s Law

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This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Bragg’s Law”.

1. The correct expression for Bragg’s law is nλ = ___________
a) dsinθ
b) dcosθ
c) 2dsinθ
d) 2dcosθ

Explanation: Bragg’s law gives us the relation between the wavelength of the incident X-ray and the angle of incidence. The expression is: nλ = 2dsinθ.

2. Peaks of scattered intensity is observed when the path difference would be equal to __________
a) λ
b) λ/2
c) 3 λ/2
d) No peaks are observed at any condition

Explanation: In the Bragg’s law experiment, the x-ray radiations are scattered by the crystal lattice. The peaks of scattered intensity are observed when the path difference is equal to the integral multiple of wavelength. Also, the incident angle should be equal to the reflecting angle.

3. Bragg’s law is used in which process?
a) X-ray production
b) Gamma-ray production
c) X-ray crystallography
d) X-ray scan

Explanation: Bragg’s law is a special case of Laue diffraction. It is used in X-ray crystallography, the basis of which is to identify the crystal lattice.
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4. When X-ray are incident on an atom, they make an electronic cloud move.
a) True
b) False

Explanation: X-ray is an electromagnetic wave. So, just like any other electromagnetic wave, when X-ray is incident on an atom, it makes the electronic cloud around that atom to move.

5. The scattering of waves in Bragg’s law experiment is due to __________
a) Einstein’s scattering
b) Rayleigh scattering
c) Newton scattering
d) Inelastic scattering

Explanation: In Bragg’s law experiment, the phenomenon is observed due to the Rayleigh scattering, i.e., the movement of charges is re-radiated with the wave of same frequency.

6. Bragg’s law is a special case of Laue diffraction.
a) True
b) False

Explanation: Laue diffraction is the one used in X-ray crystallography. Bragg’s law is only a special case of Laue diffraction with the condition that the incident angle be equal to scattering angle and the wavelength is integer times the path difference.

7. Bragg’s law was proposed in __________
a) 1903
b) 1913
c) 1893
d) 1853

Explanation: Lawrence Bragg and William Henry Bragg proposed Bragg’s law in 1913. It was based on the fact that surprising patterns are observed when the X-rays are reflected by a crystalline solid.

8. If the angle of incidence is 30°, then the wavelength for first-order spectrum is equal to __________
a) d
b) 2d
c) d/2
d) d/3

Explanation: We know, nλ = 2dsinθ.
As, θ = 30° and n = 1, we get
λ = d.

9. If X-ray of wavelength 100 Å is incident on an atom at an angle of 90°, then what should be the value of d for first-order sepctrum?
a) 30 Å
b) 40 Å
c) 50 Å
d) 60 Å

Explanation: We know, nλ = 2dsinθ.
Here, λ = 10-8 m, n = 1, sinθ = 1.
Therefore, 10-8 = 2 X d X 1
d = 50 Å.

10. What should be the value of X?

a) θ
b) θ/2
c) 2θ
d) θ/3

Explanation: As we can see in the following figure, the angle X is between the incident light and the diffracted light. This angle should be 2θ, as the angle made by both with horizontal plane would be θ.

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