Physics

Problem

In a free He

^{+}

ion

(Z=2)

initially at rest, an electron makes a transition from the third orbit to the second orbit and a photon is emitted. Using

h = 6.63\times10^{-34}\,\text{J s}

c = 3.00\times10^{8}\,\text{m s}^{-1}

, mass of the helium nucleus

M = 6.64\times10^{-27}\,\text{kg}

, and

1\,\text{eV} = 1.602\times10^{-19}\,\text{J}

, the recoil kinetic energy gained by the ion is closest to a)

7.6 \times 10^{-7}\,\text{eV}

7.6 \times 10^{-9}\,\text{eV}

1.2 \times 10^{-8}\,\text{eV}

1.2 \times 10^{-6}\,\text{eV}