A proton and an $\alpha$ particle are accelerated through a potential difference of $100\;v$ . The ratio of the wave length associated with the proton to that associated with an $\alpha$ particle is

Question

$\begin{array}{1 1} \sqrt 2 :1 \\ 2: 1\\ 2 \sqrt 2 :1 \\ \frac{1}{2 \sqrt 2} :1 \end{array} $