PHOTONS,

ELECTRONS,
AND ATOMS
PREPARED BY:
MIKKO AYSON
ALIANA CAWALING
ELLAINE MAE FLORES
JEANETTE SALVADOR
MICAH SURBANO
ALIYAH ZASPA
 LEARNING GOALS

By studying this chapter, you will learn:

• How experiments involving line spectra, the photoelectric effect, and x rays pointed the way to a
radical reinterpretation of the nature of light.
• How Einstein's photon picture of light explains the photoelectric effect.
• How the spectrum of light emitted by atomic hydrogen reveals the existence of atomic energy
levels.
• How physicists discovered the atomic nucleus.
• How Bohr's model of electron orbits explained the spectra of hydrogen and hydrogen like atoms.
• The operating principles of a laser
• How experiments with says helped confirm the photon picture of light
• How the photon picture explains the spectrum of light emitted by a hot, opaque object.
• How we can reconcile the wave and particle aspects of light.
EMISSION AND ABSORPTION OF LIGHT

Emission of light occurs when atoms or molecules release

energy in the form of photons. Absorption happens when
these entities absorb photons and gain energy, transitioning
to higher energy states. These processes are fundamental in
understanding light interactions in various phenomena, like
fluorescence or photosynthesis.
Light spectra
Substitution
• Light spectra refer to the distribution of light wavelengths
emitted or absorbed by a substance. When light passes
through a prism, it separates into different colors, creating
a spectrum.
• It was discovered early in the 19th century that each
element in it's gaseous state has a unique set of
wavelengths in its line spectrum.
Photoelectric Effect
There were also mysteries associated with absorption of light. ln 1887,
during his electro magnetic wave experiments, Hertz discovered the
photoelectric effect. When light struck a metal surface, some electrons
near the surface absorbed enough energy to overcome the attraction of
the positive ions in the metal and escape into the surrounding space.
X Rays

Other unsolved problems in the emission and absorption of

radiation centered on the production and scattering of x rays,
discovered in 1895. These rays were produced in high-voltage
electric discharge tubes, but no one understood how or why they
were produced or what determined their wavelengths (which are
much shorter those of visible light).
 Photons and energy level

Alright, let's break it down:

1. Photons: Imagine tiny bits of light called photons. They're like
little energy carriers.
2. Energy Levels: Picture electrons in an atom living on different
floors, or energy levels. The ground floor is low energy, and higher
floors mean higher energy.
3. Interaction: When electrons move between these energy levels,
they exchange energy with photons. Going up absorbs energy, and
going down emits energy in the form of photons.
The Photoelectric Effect
The photoelectric effect is the emission of electrons when light
strikes a surface. This effect has numerous practical applications. To
escape from the surface, the electron must absorb enough energy
from the incident radiation to overcome the attraction of positive
ions in the material of the surface.
Photon momentum
Example: FM radio photons
Radio station WQED in Pittsburgh broadcasts at 89.3 MHz
with a radiated power of 43.0 kW.
(a) What is the magnitude of the momentum of each photon?
(b) How many photons does WOED emit each second?
Atomic Line Spectra and Energy Levels

Photon Emission by Atom

Bohr's hypothesis represented a bold breakaway from

19th century ideas. His reasoning went like this. The
line spectrum of an element result from the Emission of
a photon, the internal energy of the atom changes by
an amount equal to the energy of the photon.
The hydrogen spectrum

By 1913 the spectrum of hydrogen, the simplest and least

massive atom, had been studied intensively. In an electric
discharge tube, atomic hydrogen emits the series of line.
The Franck-hertz Experiment

In 1914, James Franck and Gustav Hertz found even more

direct experimental evidence for the existence of atomic
energy level. Frank and Hertz studies the motion of
electrons though mercury vapor.
Energy levels

Only a few atoms and ions (such as hydrogen,singly ionized

helium,doubly ionized lithium)have spectra whose wavelengths
can be represented by a simple formula such as Balmer's. But it
is always possible to analyze the more complicated spectra of
other elements in terms of transitions among various energy
levels and deduce the numerical values of these levels from
measured spectrum wavelengths.
The Nuclear Atom

J.J Thompson had discovered the electron and measured its

charge-to-mass ratio (e/m) in 1897; by 1909, Milikan had
completed his first measurements of electron charge –e.
These and other experiments showed that almost all the
mass of an atom had to be associated with positive charge,
not with electrons.
Rutherford's Exploration of the Atom

Rutherford scattering experiments, carry out in 1910-

1911 by Earnest Rutherford and two of his students, Hans
Geiger and Earnest Marsden, at the University
Manchester in England.
The scattering of alpha particles by a thin metal foil. The source of the alpha
particles is radioactive elements such as radium. The two lead screens with
small holes form a narrow beam alpha particles, which are scattered by the
foil. The direction of the flashes on the scintillation screens.
The Bohr model is a simplified depiction of the structure of
atoms, proposed by Danish physicist Niels Bohr in 1913. It
suggests that electrons orbit the nucleus of an atom in
specific, quantized energy levels, rather than continuously
moving in any orbit. This model helped explain the stability
of atoms and laid the groundwork for understanding atomic
structure and quantum mechanics.
X-RAY PRODUCTION AND SCATTERING
Substitution

The production and scattering of x rays provide additional

examples of the quantum nature of electromagnetic radiation.
X rays are produced when rapidly moving electrons that have
been accelerated through a potential difference of the order of
10^3 V to 10^6 V strike a metal target.
First produced in 1895 by Wilhelm Rontgen (1845-1923).
X-RAY PHOTONS
Substitution
The energy of an x-ray photon is related to its frequency
and wavelength in the same way as for photons of light.

X-ray emission is the inverse of the photoelectric effect. In

photoelectric emission there is a transformation of the
energy of a photon into the kinetic energy of an electron;
in x-ray production there is a transformation of the kinetic
energy of an electron into the energy of a photon.
X-RAY PHOTONS
Substitution
In the first process, some electrons are slowed down or
stopped by the target, and part or all of their kinetic
energy is converted directly to a continuous spectrum of
photons, including x rays and this process is called
Bremsstrahlung.

The second process gives peak in the x-ray spectrum at

characteristics frequencies and wavelengths that do
depend on the target material.
COMPTON SCATTERING
Substitution
A phenomenon called Compton scattering, first explained in
1923 by the American physicist Arthur H. Compton, provides
additional direct confirmation of the quantum nature of x
rays.

When x rays strike matter, some of the radiation is scattered,

just as visible light falling on a rough surface undergoes
diffuse reflection.
APPLICATIONS OF X-RAYS
Substitution

Detects bone fractures, certain tumors and other

abnormal masses, pneumonia, some types of injuries,
calcifications, foreign objects, or dental problems.
CONTINUOUS SPECTRA
Substitution

Line spectra are emitted by matter in the gaseous state,

in which the atoms are so far apart that interactions
between them are negligible and each atom behaves as
an isolated system. Hot matter in condensed states
(solid or liquid) nearly always emits radiation with a
continuous distribution of wavelengths rather than a line
spectrum.
Bohr's Atomic Model

Atom is the smallest part of a substances that cannot be

broken down chemically. The atom is the basic particle of the
chemical elements. An atom consists of a nucleus of protons
and generally neutrons, surrounded by an electromagnetically-
bound swarm of electrons. The chemical elements are
distinguished from each other by the number of protons that
are in their atoms.
The electrons revolve rapidly around the nucleus in fixed
circular paths called energy levels or shells. The 'energy
levels' or 'shells' or 'orbits' are represented in two ways:
either by the numbers 1, 2, 3, 4, 5 and 6 or by letters K, L, M,
N, O and P. The energy levels are counted from centre
outwards.
The energy change is accompanied by absorption of
radiation energy of E = E, E, h where, h is a constant called
'Planck's constant' and is the frequency of radiation
absorbed or emitted.
Postulates of Bohr's Atomic Model

• Electrons revolve round the nucleus with definite velocities

in concentric circular orbits situated at definite distances
from the nucleus. The energy of an electron in a certain orbit
remains constant. As long as it remains in that orbit, it
neither emits nor absorbs energy. These are termed
stationary states or main energy states.
The stationary states or allowed energy levels are only
those where n = 1, 2, 3, This is called Bohr quantum
condition. The energy of an electron changes only when it
moves from one orbit to another. An electronic transition
from an inner orbit to outer orbit involves absorption of
energy. Similarly, when an electron jumps from an outer
orbit to inner orbit it releases energy, which is equal to the
difference between the two energy levels.
Rayleigh and the “Ultraviolet Catastrophe”
Rayleigh-Jeans Law

Rayleigh-Jeans law was a proposed formula that

attempted to describe the spectral radiance of a black
body at different wavelengths.
Rayleigh-Jeans Law

The law states that the intensity of the radiation emitted

by a black body is directly proportional to the temperature
and inversely proportional to the wavelength raised to a
power of four.
Mathematically, this law can be expressed as:

Here,
T is the temperature
c is the speed of light in a vacuum
k is Boltzmann's constant
Ultraviolet Catastrophe

The Rayleigh-Jeans law predicts that radiance

energy is continuous and will increase to infinity if the
wavelength gets very small. This prediction led to a
problem known as the ultraviolet catastrophe.
Planck and the Quantum Hypothesis
Quantum Hypothesis

The quantum hypothesis, first suggested by Max Planck (1858–

1947) in 1900, postulates that light energy can only be emitted
and absorbed in discrete bundles called quanta. Planck came
up with the idea when attempting to explain blackbody
radiation, work that provided the foundation for his quantum
theory.
This law can be expressed as:
Example Problem
Wave-Particle Duality

Wave-particle duality is the concept in quantum mechanics

that every particle or quantum entity may be described as
either a particle or a wave.
Quantum Electrodynamics

Quantum electrodynamics (QED) is a branch of theoretical

physics that deals with how light and matter interact at a
fundamental level.
DEMOSTRATING THE PHOTOELECTRIC EFFECT
End of presentation,

THANK
YOU.