Question

The energy required to dislodge electrons from sodium metal via the photoelectric effect is 275,what wavelength in mm of light has sufficient energy per photon to dislodge an electron from the surface of sodium

Answer 1

I got
430
n
m

Explanation:
You need
275
k
J
to dislodge one mol of electrons so we need:

275
×
10
3
6
×
10
23
=
4.6
×
10
−
19
J
for one electron only.

We can use Einstein`s relationship between energy
E
and frequency
f
and between frequency and wavelength
λ
:

E
=
h
f
=
h
c
λ

to find the wavelength (
h
is Plank`s Constant and
c
the speed of light).
We get:
λ
=
h
c
E
=
(
6.6
×
10
−
34
)
⋅
3
×
10
8
4.6
×
10
−
19
=
4.3
×
10
−
7
m
=
430
n
m