A proton and an α–particle are accelerated from rest to the same energy. The de Broglie wavelengths λp and λα are in the ratio,
4 : 1
2 : 1
1 : 1
2:1
As λ=hp=h2mKE
∴λ∝1m (Kinetic energies are same) λpλα=mαmp λpλα=4 mpmp ∴λpλα=21