19.4
λ= 3.19 x 10^-7
f = v / λ
= 3 x 10^8 / 3.19 x 10^-7
= 9.4 x 10^14
φ + KE = hf
hf= 6.24 x 10^-18
KE = 5.86 x 10^-18 J
φ= 3.78 x 10^-19


Vs=KE=Vs x q
5.86 x 10^-18= Vs x 1.6 x 10^-19
Vs = 36.6 V


19.5
f = v / λ
f= 3x10^8 / 5 x 10^-7
=6 x 10^14
φ + KE = hf
6.63 x 10^-24 x 6 x 10^14 = φ + 2.4 x 10^-15
φ= 1.878 x 10^-19 J


KE now= 9 x 10^-19 J
hf= 1.878 x 10^-19 + 9x 10^-19
= 1.0878 x 10^-18
f= 1.64 x 10^15


λ = v/f
=3 x10^8 / 1.64 x 10^15
=1.83 x 10^-7 m