\(E _{2}=\phi+ K _{2}\) \(...(2)\)

\(E _{1}- E _{2}= K _{1}- K _{2}\)

Now \(\frac{ V _{1}}{ V _{2}}=2\)

\(\frac{ K _{1}}{ K _{2}}=4\)

\(K _{1}=4 K _{2}\)

Now from equation \((2)\)

\(\Rightarrow 4-2.5=4 K _{2}- K _{2}\)

\(1.5=3 K _{2}\)

\(K _{2}=0.5 eV\)

Now putting This

Value in equation \(( 2 )\)

\(2.5=\phi+0.5 eV\)

\(\phi=2 ev\)