A Critique of the Proposed National Education Policy Reform
Fundamental particles.pptx
1. Topic for senior secondary or A-level physics students
~Lalit Kishore
2. Historical perspective
Till 19th centaury atom was considered to the fundamental
particle (ultimate: not formed by any other particles or sub-
atomic prticles)
In 20th centaury, Chadwick discovered independent neutrons
and protons...protons were found in solar flares...some stars
behaved as if they were neutron stars. Studies of cosmic rays led
to discovery of new fundamental particles
Nuclear force was – the strongest force that can could bind like
charges – studied
With high power / energy particle accelerators, very many new
particles and their anti-particles were discovered and are still
being discovered
Families / classifications/ series have created to find the missing
particles including the God particle
3. Hadrons particles
Hadrons as new fundamental particles
Quark model of hadrons with six
flavours and their charge value and
strangeness
With discovery of new particles using
particle accelerators (collision experiments)
to be classified in categories of those
affected by strong forces and those not
affected
2 conclusions from collision experiments /
nuclear reactions
Total charge always remains constant
Total number of nucleons at times but
rarely changed
The particles with properties different from
neutrons and protons discovered which
were called hadrons
From the collision studies lead to quark
model of hadrons
It was proposed that hadrons was further
made of fundamental particles called
quarks which led to discovery more
particles
Many types or ‘flavours’ (six)of quarks were
discovered and proposed
4. Hadrons’ classification as baryons
and mesons
With discovery of anti-quarks and various
combination with quarks led to new
classification of hadrons called baryons
and mesons
Baryon family : protons, Neutrons and
their anti-particles, they consist of 3
quarks
Meson family (consisting of quarks / anti-
quarks): Pions and kappas
5. Leptons
Definition and neutron
decay
Quark model reaction
The fundamental particles
not affected by strong
forces – no more composed
of smaller particles
Examples: Electron;
positron, neutrino, anti-
neutrino
In the decay of a neutron;
proton, electron and
antineutrino are emitted
6. Beta decay explanation in terms of
quarks and leptons
Weak force presence Proton decay quark model reaction
Beta decay is not due strong
force and, therefore, must be
due to another force called
‘weak force’ or ‘weak
interaction’
In beta decay, the lepton
number before and after
decay remains the same
During the decay of a proton
in the nucleus, a neutron is
formed and a neutrino is
emitted
7. Quark model facts
Quark model attributes Some quark compositions
Quark model has 6 flavours of
quark
Up
Down
Strange
Charm
Bottom
Top
Quarks have fractional charges
A meson contains a quark and
an antiquark
Baryons contain three either 3
quarks or 3 antiquarks
Protons are composed of
quarks up, up, and down
Neutrons are composed of
quarks up, up and down
During minus beta decay, a
down quark quark changes to
an up quark
During plus beta decay, an
up quark changes to a down
quark