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Figure 1 shows the apparatus used in an experiment to investigate electron diffraction and the de Broglie hypothesis - AQA - A-Level Physics - Question 1 - 2021 - Paper 7
Question 1
Figure 1 shows the apparatus used in an experiment to investigate electron diffraction and the de Broglie hypothesis. Explain how high-speed electrons are produced ... show full transcript
Worked Solution & Example Answer:Figure 1 shows the apparatus used in an experiment to investigate electron diffraction and the de Broglie hypothesis - AQA - A-Level Physics - Question 1 - 2021 - Paper 7
Step 1
Explain how high-speed electrons are produced in the apparatus in Figure 1.
Answer
Part A is the heated cathode which emits electrons when heated due to thermionic emission. Part B is the anode, which attracts the electrons due to a high positive potential. The potential difference serves to supply the energy necessary to heat the cathode for electron emission, while is responsible for accelerating the emitted electrons towards the target.
Step 2
Suggest a suitable value for $V_2$.
Answer
Considering the atomic diameter is approximately , the suitable wavelength is around . We can rearrange the equation:
ext{wavelength} = rac{h}{p}
To find , where the momentum , relating it to the energy:
ext{Energy} = eV = rac{mv^2}{2}
This suggests should be chosen around to achieve suitable electron speeds and therefore wavelengths.
Step 3
Explain how measurements made with the apparatus in Figure 1 can be used to support the de Broglie hypothesis.
Answer
Measurements of the diffraction pattern on the screen provide evidence for wave-like behavior of electrons, as predicted by the de Broglie hypothesis. The observed diffraction patterns suggest that electrons exhibit properties similar to waves, supporting the notion that they can be described with a wavelength, thus reinforcing the wave-particle duality of matter.
Step 4