An electron confined to a one$-$dimensional box has the ground state energy of $2\mathrm{.}8$ eV$.$

What is the width of the box $($in $)?($ Ans$)$Consider a neutron in a nucleus of

diameter L as a particle restricted inside a box of length L$.$ If the first energy level of this

neutron is $9\mathrm{.}35$ MeV, what is the diameter of the nucleus $($in fm$)?($Ans: $4\mathrm{.}69$ fm; $3\mathrm{.}65)$