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1. PHOTO ELECTRIC
EFFECT
PHY 209

2. PRESENTED BY
oMARIAM NAHAR MONI [2016-2-60-016]
oBONOSREE ROY [2016-2-60-097]
oS.M NAHID HASAN [2016-2-60-024]
oMOHAMMAD HEMAYET ULLAH [2016-2-60-146]
Presented to: M Ruhul Amin, Ph.D
Professor & Chairperson of Dept of MPS, EWU.

3. HISTORY
• In 1839, Alexandre Edmond Becquerel discovered the photovoltaic effect while
studying the effect of light on electrolytic cells
• When a surface is exposed to electromagnetic radiation above a certain
threshold frequency the radiation is absorbed, and electrons are emitted. This
phenomena is discovered Hertz and Hallwachs in 1887.
• In 1899, J. J. Thomson investigated ultraviolet light in Crookes tubes.
• The discovery of the ionization of gases by ultra-violet light was made by
Philipp Lenard in 1900.

4. HISTORY
• In 1905, Albert Einstein solved this apparent
paradox by describing light as composed of
discrete quanta, now called photons, rather
than continuous waves.
𝑬 = 𝒉𝝂
• This discovery led to the quantum revolution in
physics and earned Einstein the Nobel Prize in
Physics in 1921. By wave-particle duality the
effect can be analyzed purely in terms of waves
though not as conveniently.

5. WHAT IS PHOTO ELECTRIC EFFECT?
• Electromagnetic radiation can push electrons
free from the surface of a solid.
• This process is called the photoelectric effect.
• A material that can exhibit the photoelectric
effect is said to be photoemissive.
• Electrons ejected by the photoelectric effect
are called photoelectrons.

6. EXPERIMANTAL SET-UP
• Incident light triggers the emission of (photo)electrons
from the cathode.
• Some of them travel toward the collector (anode) with
an initial kinetic energy.
• The applied voltage V either accelerates (if positive) or
decelerates (if negative) the incoming electrons.
• The intensity I of the current measured by the ammeter
as a function of the applied voltage V is a measurement
of the photoelectron properties, and therefore a
measurement of the properties of the photoelectric
effect.

7. RELATION BETWEEN CURRENT AND APPLIED POTENTIAL
DIFFERENCE
• V is potential difference
• When V is positive , I increase limiting
value(saturation current) for each curve.
• When V is negative the current begins to decrease
• V0 is stopping potential. This potential is a measure
of the maximum kinetic energy of the electron.
i.e.
1
2
𝑚𝑣 𝑚
2 = 𝑒𝑉0

8. RELATION BETWEEN ENERGY OF PHOTON AND EMITTED
ELECTRON’S MAXIMUM KINETIC ENERGY
• The stopping potential V becomes zero it
indicating that no electrons are emitted
• Threshold frequency 𝑉0

9. LAWS & EQUATION OF PHOTOELECTRIC EFFECT
• 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.
𝐾 𝑚 = 𝐸 − 𝑊
𝐾𝐸 = ℎ𝜈 − ℎ𝜈0
𝐾 𝑚: maximum kinetic energy
𝐸: energy of photon’s
𝑊: Work function of metal

10. CLASSICAL PHYSICS CAN’T EXPLAIN. WHY?
• no photoelectrons are emitted when the incident light has a frequency below the
threshold,
• the maximum kinetic energy of the photoelectrons increases with the frequency
of the incident light,
• the maximum kinetic energy of the photoelectrons is independent of the intensity
of the incident light, and
• there is essentially no delay between absorption of the radiant energy and the
emission of photoelectrons.

11. USE OF PHOTOELECTRICITY

12. HAVE YOU ANY
QUESTION???

13. THANK YOU