2. Izhar Ullah
(Reg#CSEE-XF12-200)

4. OUTLINE:
Introduction.
 Laws of Photo Electric Effect.

 EINSTEIN’S
EQUATION.
 APPLICATION.

5. INTRODUCTION:
First observed by Heinrich Hertz in 1887, the
phenomenon is also known as the Hertz effect.
 Hertz observed and then showed that
electrodes illuminated with ultraviolet light
create electric sparks more easily.


6. The ejection of electrons from a metallic surface
when the light of suitable frequency is allowed
to fall on the surface.

7. • This suitable frequency is called
Threshold
Frequency
and
the
corresponding wavelength is called
threshold wavelength.
• Work function: The work function is
the energy required to remove an
electron from the highest filled level in
the Fermi distribution of a solid.

8. • Photoelectric effect is directly proportional to intensity.
•
If the frequency of the incident light is less than the
threshold frequency then no electron ejected, no
matter what the intensity.
•
The maximum kinetic energy of the electrons
depend on the frequency of the incident light.
• The electrons were emitted immediately - no time lag.

9. EINSTEIN’S EQUATIONS FOR THE
PHOTOELECTRIC EFFECT
Einstein's interpretation of the
photoelectric effect results in
equations which are valid for
visible and ultraviolet light:
energy of photon = energy
needed to remove an electron
+ kinetic energy of the emitted
electron
 hν = W + E
Where

h is Planck's constant
ν is the frequency of the
incident photon
W is the work
function, which is the
minimum energy required to
remove an electron from the
surface of a given metal: hν0
E is the maximum
kinetic energy of ejected
electrons: 1/2 mv2
ν0 is the threshold frequency
for the photoelectric effect
m is the rest mass of
the ejected electron
v is the speed of the
ejected electron

10. EINSTEIN’S EQUATIONS FOR THE
PHOTOELECTRIC EFFECT :

No electron will be emitted if the incident photon's
energy is less than the work function.

11. Km:- maximum kinetic energy
E :- energy of photon’s
W :- work function of metal

12. WORK FUNCTIONS OF SELECTED METALS
Metal
Ø (eV)
Na
2.46
Al
4.08
Cu
4.70
Zn
4.31
Ag
4.73
Pt
6.35
Pb
4.14
Fe
4.50

13. APPLICATION OF PHOTO ELECTRIC EFFECT:
 Television
Camera Tubes
 Light-Activated Counters
 Automatic Doors
 Intrusion Alarms
 Turn on Street Lights at Dawn