State the de Broglie hypothesis.

Determine the de Broglie wavelength of a proton that has been accelerated from rest through a potential difference of 1.2 kV.

Explain why a precise knowledge of the de Broglie wavelength of the proton implies that its position cannot be observed.

particles have an associated wavelength;
wavelength=\(\frac{h}{{mv}}\) or \(\frac{h}{{p}}\); (symbols must be defined)

\(\lambda  = \frac{h}{{\sqrt {2{\rm{meV}}} }}\);
8.3×10⁻¹³m;

(Heisenberg suggests that) ΔpΔx is a constant or \( \ge \frac{h}{{4\pi }}\);
if λ is known then Δp is zero therefore uncertainty in position Δx is infinite/very large;
Award [1 max] if Δp and Δx not defined.

or

(the Uncertainty Principle states that) it is impossible to know the position and momentum of a particle at the same time;
if λ is precise then momentum is precise so position is not known;