This document contains information about a team of 5 students and milestones in quantum physics. It discusses J.J. Thomson's discovery of the electron, Einstein's explanation of the photoelectric effect using the photon model, and key observations about the photoelectric effect that classical physics could not explain but quantum theory could.

2. Team Members:
1.Abubakar Siddique Monir
ID:163-15-8318
2.Md.Jahid Hasan Miah
ID:163-15-8529
3.Sahariar Islam
ID:163-15-8426
4.Mst.Sirazam Manira
ID:163-15-8466
5.Muslima Tuz Zahra
163-15-7724

5. MILESTONES OF QUANTUM PHYSICS :
J.J.Thomson Established electron as a fundamental
particle of nature. He measured its charge to mass
ratio using a Crooke's tube.
Electric current = flow of electrons
Animation of electrons moving
and being deflected by an electric
or magnetic field.
Crooke's tube:
Evacuated tube
Visualization of
electron beam

6. The other great theory of modern physics
Deals with very small objects
 Electrons, atoms, molecules
Grew out of problems that seemed simple
 Black-body radiation
 Photoelectric Effect
 Atomic Spectra
Produces some very strange results…

7. OUR QUANTUM WORLD
In the 20th century, study of atomic systems required a
fundamental revision of these classical ideas about
physical objects.
1. Light waves exhibited particle like properties –
phenomena called photo-electric effect in which light impinging
on certain metals cause instanteous emission of electrons
in a billiard ball like impact.
– the basis of automatic door openers in grocery stores
2. Electrons (particles) exhibit wave like properties – they
can pass through each other ! Phenomenon of
electron interference – basis of electron microscopes

8. The Quantum of Light or the Photon :
Particle nature of light was proposed by
Einstein in 1905 to explain the photo-electric
effect. Photo-electric effect – automatic door
openers in grocery stores. Particles of light
are called light quanta or photons
Energy of a Photon = h (frequency of
light)
h is a fundamental constant of nature and
it is
very small in size.

9. THE BOHR ATOM:
Bohr proposed a revolutionary model:
An atom with discrete (Quantum) states
– an ad hoc model
Bohr’s atom model achieved three
important results:
1. Atoms are stable
2. Different atoms of the same
element are identical.
3. Atoms regenerate if they are taken apart and
then allowed to reform.

11. Photoelectric Effect
When light shines on a
metal surface, the
surface emits electrons.
For example, I can measure a
current in a circuit just by shining a
light on a metal plate.

12. Einstein successful explained the
photoelectric effect within the
context of quantum physics.
Einstein proposed that light delivers its energy in
chunks; light consists of little particles, or quanta,
called photons, each with an energy of Planck's
constant times its frequency.
E = h f
h: Planck’s constant
F: Frequency of Radiation
E: Energy
h = 6.6 x 10-34 J.s.

13. Quantum Physics: the “quantum” comes
from quantization: we need to understand
the origin of this.
The Photoelectric Effect
metal
light
Electron
detector
electrons

14. metal
light
Electron
detector
electrons
Actual Experimental Observations:
[1] There is no delay between the light hitting the
surface and the electrons being ejected
[2] Electrons are ejected only if the incident light has a
frequency above some threshold value (i.e., it depend
on the color of the light!!)

15. Observations:
1) Number of electrons
depends on intensity
2) Energy of electrons
DOES
NOT depend on
intensity3) Cut-off frequency:
minimum frequency to
get
any emission
4) Above cut-off, energy increases
linearly with frequency

16. Observations:
1) Number of electrons depends on
intensity
2) Energy of electrons DOES NOT
depend on intensity
3) Cut-off frequency: minimum
frequency to get any emission
4) Above cut-off, energy increases
linearly with frequency
Higher intensity More quanta
Only one photon to eject
𝐾𝐸 = ℎ𝑓 − 𝜙 Einstein in 1921
Nobel Prize portra
Cited for PE Effect

17. Newtonian
Physics
Regular old classical
physics
When things get small
Quantum
physics
When things get fast Special
relativity
Quantum
field theory
Small &
fast