Question Video: Identifying Regions of Scattered Electrons in a Lattice | Nagwa Question Video: Identifying Regions of Scattered Electrons in a Lattice | Nagwa

Question Video: Identifying Regions of Scattered Electrons in a Lattice Physics • Third Year of Secondary School

The following figure shows electrons from a focused electron beam being diffracted by a crystal lattice. Within which region shown are the electrons that are scattered from atoms in the crystal? [A] Region I [B] Region II [C] Region III [D] All of the regions shown [E] None of the regions shown

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Video Transcript

The following figure shows electrons from a focused electron beam being diffracted by a crystal lattice. Within which region shown are the electrons that are scattered from atoms in the crystal? (A) Region I, (B) Region II, (C) Region III, (D) all of the regions shown, (E) none of the regions shown.

In our diagram, these blue dots represent individual atoms in the crystal lattice. A beam of electrons is focused on this lattice, and these dotted blue lines represent the paths of incoming electrons in the beam. We see three different regions here: Regions I, II, and III. And we want to identify which ones, if any, show us where are the electrons that are scattered from atoms in the crystal.

Looking first at Region I, we see that this shows us paths of electrons that are in the incoming beam. Since the electrons in this region haven’t yet reached the crystal, they can’t have scattered from it. Among our answer options then, this means we can cross out option (A) and we can also cross out option (D), which includes Region I.

Let’s look next at Region II in our diagram. We see that this region does contain electrons. But notice that the electrons in this region have not been scattered by interactions with atoms in the crystal. These electrons have passed straight through undeflected. We can’t say then that electrons in this region are scattered electrons. This means we can cross out answer option (B) from consideration.

Lastly, we look at Region III. Like the other two regions, this region also contains electrons. We see electron paths passing through it. But unlike the other regions, this one contains electrons that have indeed scattered off of atoms in the crystal. We can see that change in the path of the electrons depicted by the change in the direction of these dotted blue lines. Region III then meets our condition. This region shows us where are the electrons that are scattered from atoms in the crystal. Our final answer is option (C).

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