From Einstein's photoelectric equation, hν=ϕ+T
For metal A, 4.25 eV=ϕA+TA ...... (1)
For metal B, 4.70 eV=ϕB+TB......(2)
The de Brogile wavelength λ=1√2mT
λBλA=√TATb=2 (given)
TA=4TB, but TB=(TA−1.50) eV (given)
TA4=TA−1.50
34TA=1.50
TA=2 eV and TB=0.50 eV.
Substitute these values in equations (1) and (2).
ϕA=2.25 eV and ϕB=4.20 eV