A proton and an α-particle are accelerated, using the same potential difference. How are the de-Broglie wavelengths λp and λα  related to each other?

Hint: The de-Broglie wavelength depends on the momentum given to the particle.
Step 1: Find λ in terms of m and q.
As 
λ=h2mqvλ1mqStep 2: Find the relative wavelengths of proton and α-particle.λpλα=mαqαmpqp=4mn×2emρ×e=8λp=8λα
i.e wavelength of the proton is 8 times the wavelength of α-particle.