Question

Two charged particles having the same charge but different masses are passed through a potential difference V. When V is varied, de-Broglie wavelength (λ) of the particles varies as shown in the graph below. Which graph is for heavier particles and why?

Answer 1

λ = `h/(sqrt(2 meV))`

`λ ∝ 1/sqrtm xx 1/sqrtV`

So, in the λ vs `1/sqrtV` graph, slope ∝ `1/sqrtm`.

Heavier particles have a smaller slope (since slope ∝ `1/sqrtm`​). Therefore, line A represents the heavier particle, while line B (steeper) represents the lighter particle.