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Photoelectric Effect
Em radiation
when
:
electrons to be
causes
emitted from
surface
metals
a
1887HeinrichHer
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Em
photons
E
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.
e
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charged with
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positively charged
ecmateeddp%FE%Ee.eon.ms
( problem
envied
through photoelectric
to
become
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on
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negative high ]V
Note : this causes
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leaf
,
will fall as e
emitted and electroscope
-
power supply
neutralise s
Key Observations
.
N cannot be
explained by wave
model !
1905 : Einsteins photon model
①
④ explained observations
I
-
I
: ÷ ÷ ÷ ÷ ÷ ÷ : ÷ ÷ ÷ ÷ : ÷ :/
.
① Photoelectrons were
emitted
a
only
f was above
when
threshold frequency
This
above
.
ie
electrons
.
instantaneous
was
were
not
'
!
up
③ If the incident radiation was
the threshold f , the
emission
regardless of
was
Intensity
② If incident radiation was
energy
'
.
building
increasing the intensity of
the EM
① The energy supplied by the ④ Each e- requires
radiation is not due
to
intensity 1
amount
brightness
which
a
certain
radiation did not
more
instead
were
caused
emitted
.
of E to be emitted
f did
KE
.
more
Only by increasing
have more KE
the e-
supplied by
must be
will emit
necessarily
they do
E each
have
enough
not
no
time
an
e- There is
delay
.
dependent on
is left
.
.
of emission a Iof
after
over
is
emitted
to
emit e- is the
the
work
.
key Ideas
→
a
( for photons)
f
② It is a
one
③ AS IT
rate
,
-
to
-
of
one
-
e
e-
The E needed
.
~
① E
E
how much
function ¢ [minimum EI
incident EM radiation
Three
e-
:÷÷÷÷÷÷÷÷÷÷
the metal per second but
Rate
e-
give
.
It
Em
the threshold f then
above
interaction
between
emission increases
.
a
photon and e-
.
.
|
Einstein
applied
the
conservation
Energy of each photon would
I
Free
.
2
e
an
-
Remaining e
-
.
work function
in
a
one
-
transferred
the
to
-
one
interaction
KE
of e-
to
:
.hf=dtkEm
✓
~
electron
an
Max
If
a
use
a
consistent
unit
for
photoelectron strikes with fo
,
all
no
.
(
e.g
.
KE
a
particular metal
nrsjinneyreradgiubirinomto.ae Insane a' Eons: emitted
"
work function
energy
from
K E
"
UNITS : must
.
.
¢ minimum energy required to free
energy of photon
photoelectric effect
( above d)
:
to
of energy
↳
they
are
the metal
'
-
closer to
'
positive ions in
.
eV or J)
is
transferred
so :
hf
::*
Graphical Representation
KE max N
-
I
;
f too low
teemed
i
Rearranging the equation gives
µ Ema.
:
,
=
④g ④
4.
-
I
's intercept
-
'
a.em
pairing
'
gradient
v
.
I
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"
"
'
¢
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