AP EAMCET Engineering 22 Apr 2019 Shift 1 Paper

The energy of the incident light is calculated as,
E=

hc

λ

E=

6.6×10−34×3×108

4×10−7

J
E=

4.95×1019

1.6×10−19

eV
E≈31eV
The acceleration (retardation) of the emitted electrons in the electric field is,
a=

qE

m

The initial speed of the electron is,
v2=u2−2as
(0)2=u2−2(

qE

m

)(1)
u2=

2qE

m

The maximum kinetic energy of the electron is calculated as,
Kmax=

1

2

mu2
Kmax=

1

2

m(

2qE

m

)
Kmax=qE
Kmax=(1.6≈10−19)(2)
Kmax=3.2≈10−19 J=2eV
So, the work function of the surface is,
W0=E−Kmax
W0=3.1−2
W0=1.1eV