CERTIFICATE

This is to certify that this project to work and titled photoelectric effect
is submitted by Anmol Malhotra for completion of his physics project
work for requirement of practical examination by CBSE New Delhi

Anmol has worked under my supervision and his project work is

complete for submission

Anmol carried out the work assigned him very sincerely

Anmol carried my best wishes

Ms. Preeti
(PGT Physics)

ACKNOWLEDGEMENT
I would like to express my heartfelt gratitude to everyone who contributed to
the successful completion of this project.

First and foremost, I am deeply thankful to Ms. Preeti Solanki (PGT Physics)
for their invaluable guidance, encouragement, and support throughout this
project. Their insightful feedback and expertise helped shape this work and
provided me with a clearer understanding of the subject.

I would also like to thank Dr. Vijay Pal, Principal, DAV Centenary Public School,
Kalanaur for providing the necessary resources and a conducive learning
environment to carry out this project.

Finally, I am immensely grateful to my family for their unwavering support,

patience, and motivation throughout this journey. Their belief in my abilities has
been my greatest source of strength.

Thank you all for being a part of this learning experience.

Name: Anmol Malhotra

Class:XII

INDEX
SL PAGE
DESCRIPTION
NO NO
 1 HISTORY 05

2 WHAT IS PHOTON.? 07

3 PHOTOELECTRIC EFFECT 08

EXPRIMENTAL SET-UP TO STUDY PHOTOELECTRIC

4 10
EFFECT

EFFECT OF INTENSITY, FREQUENCY,POTENTIAL ON

5 11
P.E. CURRENT

6 LAWS OF PHOTOELECTRIC EMISSION 15

7 EINSTEIN’S PHOTOELECTRIC EQUATION 16

VERIFICATION OF LAWS OF PHOTOELECTRIC EFFECT

8 18
BASED ON EINSTEIN’S PHOTOELECTRIC EQUATION

9 APPLICATION OF PHOTOELECTRIC EFFECT 19

History of Photoelectric
Effect:
Before Albert Einstein explained the matter, several scientists
made similar observations but were unable to clarify the concept.
In the 1800s, James Clark Maxwell and Hendrik Lorentz of
Scottish and Dutch origin resolved that light behaves like a wave.
The theory was proven when light waves demonstrated
interference, scattering, and diffraction. German physicist Heinrich
Rudolf Hertz, in 1887, discovered the photoelectric effect.
Regarding the theory of radio waves, Heinrich’s observation
claimed that sparking takes place when two metal electrodes are
shone with ultraviolet light, there is a voltage change because of
the light.

In 1899, JJ Thompson discovered that if ultraviolet light is being

hit on a metal surface, then it causes electron ejection. Another
scientist Philipp Lenard, in 1902, clarified the connection between
electricity and light, which further proved the theory of the
photoelectric effect. There are further studies conducted on the
subject that strengthened the connection between matter which
can’t be explained by physics and light. This relation described
light as an electromagnetic wave. Einstein conveyed that light is
made up of small packets, which were initially called quanta but
later named photons.
Theoretical studies were done by Arthur Compton in 1922 further
proved that X-rays could be treated as photons. He earned the
Nobel Prize in 1927 for the same. In 1931, Ralph Howard Fowler
did theoretical studies to link photoelectric currents with metal
temperatures.

Photon
A packet or bundle of energy is called a photon.
Energy of a photon is E = 𝒉𝒄/ 𝛌 = hν
where h is the Planck’s constant, ν is the frequency of the
radiation or photon, c is the speed of light (e.m. wave) and λ is
. the wavelength
Properties of photons:

i) A photon travels at a speed of light c in vacuum. (i.e. 3 x 10-8 m/s)

ii) It has zero rest mass. i.e. the photon can not exist at rest.

iii) Photons are not deviated by magnetic and

electric fields.

iv) The momentum of a photon is, p = 𝑬/𝒄 = 𝒉/ 𝛌

v) Photons travel in a straight line.

vi) Energy of a photon depends upon frequency of the photon; so the

energy of the photon does not change when photon travels from
one medium to another.

vii) Wavelength of the photon changes in different media; so,

velocity of a photon is different in different media.

viii) Photons are electrically neutral.

ix) Photons may show diffraction under given conditions.

Photoelectric Effect:
➢ The phenomenon of emission of electrons from mainly
metal surfaces exposed to light energy (X – rays, γ –
rays, UV rays, Visible light and even Infra Red rays) of
suitable frequency is known as photoelectric effect.

➢ The electrons emitted by this effect are called

photoelectrons.
 ➢ The current constituted by photoelectrons is known
as photoelectric current.

Note: Non metals also show photoelectric effect.

Liquids and gases also show this effect but to limited
extent.

Characteristics Of Photoelectric
Effect

• The threshold frequency varies with material, it is

different for different materials.
• The photoelectric current is directly proportional to the
light intensity.
• The kinetic energy of the photoelectrons is directly
proportional to the light frequency.
 • The stopping potential is directly proportional to the
frequency and the process is instantaneous.

Factors affecting Photoelectric

Effect
1. The intensity of incident radiation.
2. A potential difference between metal plate and collector.
3. Frequency of incident radiation.

Conditions for the Photoelectric

Effect
The minimum condition required for the emission of electrons
from the outermost shell of an atom is that the frequency of
incident rays should be very high. This will provide energy to
the electron to leave its outermost shell.

Importance of the Photoelectric

Effect
The study of the photoelectric effect has led to expanding our
understanding of the quantum nature of light and electrons.
It has further influenced the formation of the concept of
wave-particle duality. The photoelectric effect is also widely
used to investigate electron energy levels in the matter
Experimental Set-up to study
Photoelectric Effect:

➢ Glass transmits only visible and infra-red lights

but not UV light.

➢ Quartz transmits UV light.

➢ When light of suitable frequency falls on the
metallic cathode, photoelectrons are emitted.
These photoelectrons are attracted towards the
+ve anode and hence photoelectric current is
constituted.

Effect of (Intensity) of Incident Light on

Photoelectric Current:
➢ For a fixed frequency, the photoelectric current
increases linearly with increase in intensity of
 incident light.

Effect of (Potential) on Photoelectric

Current:
➢ For a fixed frequency and intensity of incident light,
the photoelectric current increases with increase in
+ve potential applied to the anode.

➢ When all the photoelectrons reach the plate A, current

becomes maximum and is known as saturation
current.

➢ When the potential is decreased, the current

decreases but does not become zero at zero potential.

➢ This shows that even in the absence of accelerating

potential, a few photoelectrons manage to reach the
plate on their own due to their K.E.

➢ When –ve potential is applied to the plate A w.r.t. C,

photoelectric current becomes zero at a particular
value of –ve potential called stopping potential or
cutoff potential.

➢ Intensity of incident light does not affect the stopping

potential.
Effect of Frequency of Incident Light on
Photoelectric Current:
➢ For a fixed intensity of incident light, the photoelectric
current does not depend on the frequency of the
➢ incident light. Because, the photoelectric current
simply depends on the number of photoelectrons
emitted and in turn on the number of photons incident
and not on the energy of photons.
Effect of Frequency of Incident Light on
Stopping Potential:
➢ For a fixed intensity of incident light, the photoelectric
current increases and is saturated with increase in +ve
potential applied to the anode.

➢ However, the saturation current is same for different

frequencies of the incident lights.

➢ When potential is decreased and taken below zero,

photoelectric current decreases to zero but at different
stopping potentials for different frequencies.

(Higher the frequency, higher the stopping potential. i.e. V S α ν)

Threshold Frequency:
➢ The graph between stopping potential and
frequency does not pass through the origin. It
shows that there is a minimum value of
frequency called threshold frequency below
which photoelectric emission is not possible
however high the intensity of incident light may
be. It depends on the nature of the metal emitting
photoelectrons.
Laws of Photoelectric Emission:
i) For a given substance, there is a minimum value of
frequency of incident light called threshold frequency
below which no photoelectric emission is possible,
howsoever, the intensity of incident light may be.

ii) The number of photoelectrons emitted per second (i.e.

photoelectric current) is directly proportional to the
intensity of incident light provided the frequency is
above the threshold frequency.
 iii) The maximum kinetic energy of the photoelectrons is
directly proportional to the frequency provided the
frequency is above the threshold frequency.

iv) The maximum kinetic energy of the photoelectrons is

independent of the intensity of the incident light.

v) The process of photoelectric emission is

instantaneous. i.e. as soon as the photon of suitable
frequency falls on the substance, it emits
photoelectrons.

vi) The photoelectric emission is one-to-one. i.e. for every

photon of suitable frequency one electron is emitted.

Einstein’s Photoelectric Equation:

When a photon of energy hν falls on a metal surface,
the energy of the photon is absorbed by the electron
and is used in two ways:
➢ A part of energy is used to overcome the surface
barrier and come out of the metal surface. This part of
the energy is called ‘work function’ (Ф = hν0).

➢ The remaining part of the energy is used in giving a

velocity ‘v’ to the emitted photoelectron. This is equal
to the maximum kinetic energy of the photoelectrons
( ½ mv2 max ) where ‘m’ is mass of the photoelectron.
According to law of conservation of energy,

hν = Ф + ½ mv2max
= hν0 + ½ mv2max

½ mv2 max = h ( ν - ν0 )

Relationship between the Frequency

of the
Incident Photon and the Kinetic
Energy of the Emitted Photoelectron :
Therefore, the relationship between the energy of the
photon and the kinetic energy of the emitted
photoelectron can be written as follows.

Ephoton = Φ + Eelectron
⇒ h𝜈 = h𝜈th + ½mev2
Where,
• Ephoton denotes the energy of the incident photon, which is
equal to h𝜈.
• Φ denotes the threshold energy of the metal surface, which
is equal to h𝜈th.
• Eelectron denotes the kinetic energy of the photoelectron,
which is equal to ½mev2 (me = mass of electron = 9.1*10-31
kg).

➢ If the energy of the photon is less than the threshold

energy, there will be no emission of photoelectrons (since the

overcome). Thus, the photoelectric effect will not occur if 𝜈 <

attractive forces between the nuclei and the electrons cannot be

𝜈th. If the frequency of the photon is exactly equal to the

threshold frequency (𝜈 = 𝜈th), there will be an emission of
photoelectrons, but their kinetic energy will be equal to zero. An
illustration detailing the effect of the frequency of the incident
light on the kinetic energy of the photoelectron is provided
below.

Verification of Laws of Photoelectric Emission

based on Einstein’s Photoelectric Equation:

½ mv2 max = h ( ν - ν0 )
i) If ν < ν0, then ½ mv2 max is negative, which is not
possible. Therefore, for photoelectric emission to
take place ν > ν0.

ii) Since one photon emits one electron, so the

number photoelectrons emitted per second is
directly proportional to the intensity of incident
light.

iii) It is clear that ½ mv2 max α ν as h and ν0 are

constant. This shows that K.E. of the
photoelectrons is directly proportional to the
frequency of the incident light.

iv) Photoelectric emission is due to collision

between a photon and an electron. As such there
can not be any significant time lag between the
incidence of photon and emission of
photoelectron. i.e. the process is instantaneous.
It is found that delay is only 10-8 seconds.
 Application of Photoelectric
Effect:
1. Automatic fire alarm
2. Automatic burglar alarm
3. Scanners in Television transmission
4. Reproduction of sound in cinema film
5. In paper industry to measure the thickness of paper
6. To locate flaws or holes in the finished goods
7. In astronomy
8. To determine opacity of solids and liquids
9. Automatic switching of street lights
10.To control the temperature of furnace
11.Photometry
12.Beauty meter – To measure the fair complexion of skin

13.Light meters used in cinema industry to check the light

14.Photoelectric sorting

15.Photo counting
16.Meteorology
THANK
YOU