University PhySICS Mongo Freeman Modern Physics
Chapter 38 Photons :
Light Waves Behaving as Particles
Photoeletric Effect when light is absorbed by a surface a causes electrons to be ejected
ejected electrons form a photocurrent
stopping
magnitude -potential
W
Prevency
of electron
CVo hf - I
charge
eVo
4
= * greater work function -
smaller photoelectron energy
, ,
-work
function
photoelection max energy of
absorbed
kinetic
energy photon
Experiment Results
1) photocurrent depends on the light frequency monochromatic light wh freq . below min threshold does not brod . photocurrent
where Vo & f graph meets o on X axis
2) no measurable time delay btw light turned on
a cathode
emitting photoelections
assuming freq . exceeds min threshold frequency , no matter how dim light is
3) stopping potential does NOT depend on
intensity
, but does depend on frequency
↳ effectively voltage
↳ units : volts
(E)
Work Vo(V)
[ 3
O
Wrot = -
eVo = k = 0 -
Kmax stopping potential
intensity
const
is independent
·
-
2 &
of intensity
Kmax EMVmax eVo =
hf Q-
-
inreshold
= =
work function
stopping
&
frequency O
min energy required
to eject electron potential
-
vo g
Vac
work
O o
function
0 25
.
0 5
.
05
If
* reverse potential difference a stopping potential C
-
-
10
na
Energy of a Photon E =
hf =
X
N
Momentum of a Photon p
=
E = =
/I
Plank's constant n =
6 626
.
x 1535 J 5 .
=
2 .
136x10-1 eVs
Ex 38 2 . .
Vo =
1 25V
.
a) Kmax =? =
eVo =
(1 .
60 x 10 - (J) (1 .
25 [v]) =
2 00 .
x 10. [5] =
e(1 25 [v]) .
=
1 25
. e
b) Vmax =? Kmax =
EMUmax
2 kmax 2(2 00 10 19)
-
. x
-
m
-
m
~ 6x105 m/s
382 X-Ray
Production / bectrons released & v .
high speeds by heated cathode slam into anode a momentum immediately goes to turoa
I/x) X-ray indensity X-rays are produced
X
50kV
40kV
Bremstrahling eVac =
ufmax =
max
Radiation
I(pc)
/
X-ray wavelength
12
(pc 10
-
= m
Chapter 38 Photons :
Light Waves Behaving as Particles
Photoeletric Effect when light is absorbed by a surface a causes electrons to be ejected
ejected electrons form a photocurrent
stopping
magnitude -potential
W
Prevency
of electron
CVo hf - I
charge
eVo
4
= * greater work function -
smaller photoelectron energy
, ,
-work
function
photoelection max energy of
absorbed
kinetic
energy photon
Experiment Results
1) photocurrent depends on the light frequency monochromatic light wh freq . below min threshold does not brod . photocurrent
where Vo & f graph meets o on X axis
2) no measurable time delay btw light turned on
a cathode
emitting photoelections
assuming freq . exceeds min threshold frequency , no matter how dim light is
3) stopping potential does NOT depend on
intensity
, but does depend on frequency
↳ effectively voltage
↳ units : volts
(E)
Work Vo(V)
[ 3
O
Wrot = -
eVo = k = 0 -
Kmax stopping potential
intensity
const
is independent
·
-
2 &
of intensity
Kmax EMVmax eVo =
hf Q-
-
inreshold
= =
work function
stopping
&
frequency O
min energy required
to eject electron potential
-
vo g
Vac
work
O o
function
0 25
.
0 5
.
05
If
* reverse potential difference a stopping potential C
-
-
10
na
Energy of a Photon E =
hf =
X
N
Momentum of a Photon p
=
E = =
/I
Plank's constant n =
6 626
.
x 1535 J 5 .
=
2 .
136x10-1 eVs
Ex 38 2 . .
Vo =
1 25V
.
a) Kmax =? =
eVo =
(1 .
60 x 10 - (J) (1 .
25 [v]) =
2 00 .
x 10. [5] =
e(1 25 [v]) .
=
1 25
. e
b) Vmax =? Kmax =
EMUmax
2 kmax 2(2 00 10 19)
-
. x
-
m
-
m
~ 6x105 m/s
382 X-Ray
Production / bectrons released & v .
high speeds by heated cathode slam into anode a momentum immediately goes to turoa
I/x) X-ray indensity X-rays are produced
X
50kV
40kV
Bremstrahling eVac =
ufmax =
max
Radiation
I(pc)
/
X-ray wavelength
12
(pc 10
-
= m
