Answer:
8.59
⋅
10
17
Explanation:
You can start by figuring out the energy of a single photon of wavelength
505 nm
=
505
⋅
10
−
9
m
.
To do that, use the equation
E
=
h
⋅
c
λ
Here
h
is Planck's constant, equal to
6.626
⋅
10
−
34
.
J s
c
is the speed of light in a vacuum, usually given as
3
⋅
10
8
.
m s
−
1
λ
is the wavelength of the photon, expressed in meters
Plug in your value to find--notice that the wavelength of the photon must be expressed in meters in order for it to work here.
E
=
6.626
⋅
10
−
34
J
s
⋅
3
⋅
10
8
m
s
−
1
505
⋅
10
−
9
m
E
=
3.936
⋅
10
−
19
J
So, you know that one photon of this wavelength has an energy of
3.936
⋅
10
−
19
J
and that your laser pulse produces a total of
0.338 J
of energy, so all that you need to do now is to find how many photons are needed to get the energy output given to you.
0.338
J
⋅
1 photon
3.936
⋅
10
−
19
J
=
8.59
⋅
10
17
photons
−−−−−−−−−−−−−−−−−
The answer is rounded to three sig figs.
