When photons of wavelength ${\lambda _1}$ are incident on an isolated sphere, the corresponding stopping potential is found to be V. When photons of wavelength ${\lambda _2}$ are used, the corresponding stopping potential was thrice that of the above value. If light of wavelength ${\lambda _3}$ is used then find the stopping potential for this case :
${{hc} \over e}\left[ {{1 \over {{\lambda _3}}} - {1 \over {{\lambda _2}}} - {1 \over {{\lambda _1}}}} \right]$
${{hc} \over e}\left[ {{1 \over {{\lambda _3}}} + {1 \over {{\lambda _2}}} - {1 \over {{\lambda _1}}}} \right]$
${{hc} \over e}\left[ {{1 \over {{\lambda _3}}} + {1 \over {2{\lambda _2}}} - {3 \over {2{\lambda _1}}}} \right]$
${{hc} \over e}\left[ {{1 \over {{\lambda _3}}} + {1 \over {2{\lambda _2}}} - {1 \over {{\lambda _1}}}} \right]$
