Physics 9702 · AS & A Level · Wave-particle duality
Wave-particle duality — practice question
Electrons in a vacuum begin from rest and are accelerated by a potential difference (p.d.) $V$ so that a beam is produced. Each electron has mass $m$ and charge $q$. This beam is directed at a graphite crystal, which serves as a diffraction grating. After it passes through the crystal, the beam arrives at a fluorescent screen, where an interference pattern is seen.
(a)[1]
Explain what this observation reveals about the nature of electrons.
(b)[3]
Determine an expression, in terms of $m$, $q$ and $V$, for the momentum $p$ of an electron in the beam.
(c)[2]
The p.d. through which the electrons are accelerated is now increased to a larger value. Describe and explain the effect of this change on the interference pattern observed.
(d(i))[2]
On Fig. 9.1, sketch how $p$ varies with $\frac{1}{\lambda}$.
(d(ii))[1]
State the name of the quantity that the gradient of the line in Fig. 9.1 represents.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “The diffraction pattern shows that electrons have wave behaviour.” …