For a certain metal, when monochromatic light of wavelength λ is incident, the stopping potential for photoelectrons is 3 V_o. When the same metal is…

For a certain metal, when monochromatic light of wavelength $\displaystyle \lambda$ is incident, the stopping potential for photoelectrons is $\displaystyle 3 \mathrm{V}_o$. When the same metal is illuminated by light of wavelength $\displaystyle 2 \lambda$, then the stopping potential becomes $\displaystyle \mathrm{V}_o$. The threshold wavelength for photoelectric emission for the given metal is $\displaystyle \alpha \lambda$. The value of $\displaystyle \alpha$ is $\displaystyle \_\_\_\_$.