A proton is fired from very far away towards a nucleus with charge Q = 120 e, where e is the electronic charge. It makes a closest approach of 10 fm to the nucleus. The de Broglie wavelength (in units of fm) of the proton at its start is : (take the proton mass, m_p = (5/3) × 10^–27 kg ; h/e = 4.2 × 10^–15 J.s/C ;
 $\frac{1}{4{\mathrm{\pi \epsilon }}_0}$  = 9 × 10⁹ m/F ; 1fm = 10^–15 m)