\(K _{2}=\frac{1.5}{2} h { v }_ 0- h v_ 0=-0.25 h v_{ 0}\)
\(\because\) Kinetic energy can never be negative So, no emission and \(i=0\)
OR
In second case the incident frequency is halved
Incident frequency \(=\frac{1.5}{2} v_{0}=0.75 v _{0}\)
Now the incident frequency is less than threshold frequency so no emission of electron take place therefore no current. \((i=0)\)