As , `eV_0=(hc)/lambda-phi_0`,
so `2.5V_0e=(hc)/lambda-phi_0.....(i)`
and `V_0e=(hc)/(1.5lambda)-phi_0.....(ii)`
From (i),
`eV_0=(hc)/(2.5lambda)-(phi_0)/2.5......(iii)`
From (ii) and (iii),
`(hc)/(1.5lambda)-phi_0=(hc)/(2.5lambda)-(phi_0)/2.5`
or `(hc)/lambda[1/1.5-1/2.5]=phi_0(1-1/2.5)=1.5/2.5 phi_0=3/5phi_0`
of `(hc)/lambda[10/15-10/25]=3/2 (hc)/(lambda_0)`
or `(hc)/lambda[4/15]=3/5 (hc)/(lambda_0)`
or `lambda_0=9/4 lambda=2.25lambda`