An atom absorbs a photon of wavelength 500 nm and emits another photon of wavelength 600 nm. The net energy absorbed by the atom in this process is $n \times 10 ^ { - 4 } \mathrm { eV }$. The value of $n$ is [Assume the atom to be stationary during the absorption and emission process] (Take $h = 6.6 \times 10 ^ { - 34 } \mathrm {~J} \cdot \mathrm {~s}$ and $c = 3 \times 10 ^ { 8 } \mathrm {~m} \mathrm {~s} ^ { - 1 }$).