PHYSICS: PARTICLE PHYSICS
Overview- The atom was discovered by John Dalton in 1802
- However, even more fundamental particles were discovered in the 20th century
- Particle physics focuses on subatomic particles including electrons, protons and neutrons
- Many fundamental particles do not occur in nature but can be created in high energy collisions of other particles
Standard Model of particle physics
- The Standard Model describes the current classification of elementary particles
- It describes strong, weak and electromagnetic forces using gauge bosons
- The Standard Model does not include gravitation, dark matter and dark energy
- The Standard Model was developed by Sheldon Glashow, Steven Weinberg and Abdus Salam in the 1960s. They won Nobel in Physics in 1979
- The Model contains 24 fundamental particles
- It predicts the existence of the Higgs Boson, which is yet to discovered
- All particles of the Standard Model have been observed in experiments, except the Higgs Boson
Elementary particles
- All elementary particles are either fermions or bosons
- Fermions are particles associated with matter, while bosons are particles associated with force
- Fermions can be divided into Quarks and Leptons
- Bosons can be divided into Gauge Bosons and Other Bosons (including Higgs Boson)
- Protons and neutrons are examples of Hadrons, which are composites of Quarks
- Electrons are elementary particles by themselves
PHYSICS: NUCLEAR PHYSICS
Nuclear Fission
- Nuclear fission is a reaction in which the nucleus of an atom splits into smaller parts
- Nuclear fission can either release energy or absorb energy: for nuclei lighter than iron fission absorbs energy, while for nuclei heavier than iron it releases energy
- Energy released can be in the form of electromagnetic radiation or kinetic energy
- The amount of free energy contained in nuclear fuel is about a million times that contained in a similar mass of chemical fuel (like petrol)
- The atom bomb or fission bomb is based on nuclear fission
- Example: fission of Uranium-235 to give Barium, Krypton and neutrons
Nuclear Fusion
- Nuclear fusion is the process by which multiple nuclei join together to form a heavier nucleus
- Nuclear fusion can result in either the release or absorption of energy: for nuclei lighter than iron fusion releases energy, while for nuclei heavier than iron it absorbs energy
- Nuclear fusion is the source of energy of stars.
- Nuclear fusion is responsible for the production of all but the lightest elements in the universe. This process is called nucleosynthesis
- Controlled nuclear fusion can result in a thermonuclear explosion – the concept behind the hydrogen bomb
- The energy density of nuclear fusion is much greater than that of nuclear fission
- Only direct conversion of mass into energy (collision of matter and anti matter) is more energetic than nuclear fusion
- Example: fusion of hydrogen nuclei to form helium
PIONEERS OF NUCLEAR PHYSICS RESEARCH
| Scientist | Nationality | Discovery | Recognition |
| J J Thomson | Britain | Electron (1897) | Nobel in Physics (1906) |
| Henri Becquerel | Belgium | Radioactivity (1896) | Nobel in Physics (1903) |
| Ernest Rutherford | New Zealand | Structure of atom (1907) | Nobel in Chemistry (1908) He is regarded as the father of nuclear physics |
| Franco Rasetti | Italy/USA | Nuclear spin (1929) | |
| James Chadwick | Britain | Neutron (1932) | Nobel in Physics (1935) |
| Enrico Fermi | Italy/USA | Nuclear chain reaction (1942) Neutron irradiation | Nobel in Physics (1938) |
| Hideki Yukawa | Japan | Strong nuclear force (1935) | Nobel in Physics (1949) |
| Hans Bethe | Germany/USA | Nuclear fusion (1939) | Nobel in Physics (1967) |
APPLICATIONS OF NUCLEAR PHYSICS
Application | Developed by | Working principle | Use |
Nuclear power | Enrico Fermi (Italy, 1934) | Nuclear fission | Power generation |
Nuclear weapons | Enrico Fermi (Italy, 1934) Edward Teller (USA, 1952) | Nuclear fission Nuclear fusion | Weapons |
Radioactive pharmaceuticals | Sam Seidlin (USA, 1946) | Radioactive decay | Cancer, endocrine tumours, bone treatment |
Medical imaging | David Kuhl, Roy Edwards (USA, 1950s) | Nuclear magnetic resonance (for MRI) Positron emission (for PET) | MRI: Musculosketal, cardiovascular, brain, cancer imaging PET: cancer, brain diseases imaging |
Radiocarbon dating | Willard Libby (USA, 1949) | Radioactive decay of carbon-14 | Archaeology |
IMPORTANT NUCLEAR RESEARCH FACILITIES
Nuclear research facilities in the world| Facility | Location | Established | Famous for |
| Brookhaven National Lab | New York | 1947 | Until 2008 world’s largest heavy-ion collider |
| European Organization for Nuclear Research (CERN) | Geneva | 1954 | World’s largest particle physics lab Birthplace of the World Wide Web Large Hadron Collider (LHC) |
| Fermilab | Chicago | 1967 | Tevatron – world’s second largest particle accelerator |
| ISIS | Oxfordshire (England) | 1985 | Neutron research |
| Joint Institute for Nuclear Research | Dubna, Russia | 1956 | Collaboration of 18 nations including former Soviet states, China, Cuba |
| Lawrence Berkeley National Lab | California | 1931 | Discovery of multiple elements including astatine, and plutonium |
| Lawrence Livermore National Lab | California | 1952 | |
| Los Alamos National Lab | New Mexico, USA | 1943 | The Manhattan Project |
| National Superconducting Cyclotron lab | Michigan | 1963 | Rare isotope research |
| Oak Ridge National Lab | Tennessee | 1943 | World’s fastest supercomputer – Jaguar |
| Sudbury Neutrino Lab | Ontario | 1999 | Located 2 km underground Studies solar neutrinos |
| TRIUMF (Tri University Meson Facility) | Vancouver | 1974 | World’s largest cyclotron |
| Yongbyon Nuclear Scientific Research Centre | Yongbyon, North Korea | 1980 | North Korea’s main nuclear facility |
| Sandia National Lab | New Mexico, USA | 1948 | Z Machine (largest X-ray generator in the world) |
| Institute of Nuclear Medicine, Oncology and Radiotherapy (INOR) | Abbottabad, NWFP (Pakistan) | ||
| Pakistan Institute of Nuclear Science and Technology (PINSTECH) | Islamabad | 1965 |
Nuclear research facilities in India
Facility | Location | Established | Famous for |
Bhabha Atomic Research Centre | Bombay | 1954 | India’s primary nuclear research centre India’s first reactor Apsara |
Variable Energy Cyclotron Centre (VECC) | Calcutta | 1977 | First cyclotron in India |
Institute for Plasma Research (IPR) | Gandhinagar | 1982 | Plasma physics |
Indira Gandhi Centre for Atomic Research (IGCAR) | Kalpakkam | 1971 | Fast breeder test reactor (FBTR) KAMINI (Kalapakkam Mini) light water reactor Built the reactor for Advanced Technology Vessel (ATV) |
Saha Institute for Nuclear Physics | Calcutta | 1949 | |
Tata Institute for Fundamental Research (TIFR) | Bombay | 1945 |
PHYSICS: OPTICS IN EVERYDAY LIFE
Working of the Human Eye- Light entering the eye passes through the cornea and the pupil
- Then, the lens focuses light onto an array of photoreceptor cells in the back of the eye, called the retina
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There are two types of photoreceptor cells:- Rod cells: they are responsible for black and white vision, night vision and peripheral vision. They are more in number
- Cone cells: they are responsible for colour vision. They are less numerous in number
Defects in vision
- Presbyopia: as people age, the lens becomes less flexible and near point recedes from the eye. As a result objects far away cannot be see. Can be corrected using a converging lens
- Hyperopia: lens cannot decrease focal length to focus on nearby objects and so nearby objects cannot be see. Corrected using a converging lens
- Myopia: lens cannotincrease focal length to focus on far away objects and so farther objects cannot be seen. Corrected using a diverging lens
- Astigmatism: occurs when the cornea is not spherical but instead elongated. Results in distorted images. Corrected using a cylindrical surface lens
Applications of Mirrors
- Kaleidoscope: A toy in which multiple images are formed by two mirrors placed inside a tube
- Periscope: Two plane mirrors fixed facing each other 45 degrees. Used in submarines
- Concave mirror: When used close to face gives magnified image. Used for shaving, personal care etc
- Convex mirror: Produces smaller image but gives wider range of view. Used in rear view mirrors
- Parabolic mirror: A concave mirror whose section is the shape of a parabola, helps in focusing. Used as reflectors in search lights, car head lights etc
Optical instruments and their applications
| Instrument | Working principle | Applications |
| Microscope | Convex lens (converging lens) system consisting of very short focal length eyepiece and longer focal length objective | Magnifying tiny objects: molecular studies |
| Telescope | Convex lens system that provides regular magnification | Magnifying distant objects: astronomy |
| Binocular | Pair of telescopes mounted side-by-side | General use |
| Interferometer | Superposition of waves | To study interference properties of light |
| Photometer | Uses a light sensitive element (like photomultiplier) to measure light intensity | Used to measure reflection, scattering, fluorescence etc |
| Polarimeter | Light from a source passing through a polarizer and then measured | Measures dispersion or rotation of polarized light |
| Spectrometer | Works by measuring light intensity | Used to measure light properties: astronomy |
| Autocollimator | Projects and image onto a target mirror and measures deflection of returned image | Component alignment, measure deflection in optomechanical systems |
Optics in the atmosphere
| Observed effect | Underlying cause | Description |
| Blue colour of sky | Rayleigh scattering | Higher frequencies (blue light) get more scattered than lower frequencies |
| Red colour of sunrise and sunset | Mei scattering | Scattering due to suspended particles (like dust) when sun’s rays have to travel longer distance |
| Halos/afterglows | Scattering | Scattering off ice particles |
| Sundog | Scattering | Scattering off ice crystals causing bright spots on the sky |
| Mirage | Refraction | |
| Novaya Zemlya effect | Refraction | Sun appears to rise earlier than predicted |
| Fata Morgana | Refraction due to temperature inversion | Objects beyond the horizon can be seen elevated |
| Rainbow | Total internal reflection |
Optics for photography
| Desired effect | Approach |
| Close up | Use macro lens |
| Long shot | Telephoto lens |
| Panoramic pictures | Wide angle lens |
| Handle low light conditions | Increase exposure time (decrease shutter speed) |
| Fast moving objects | Decrease exposure speed (increase shutter speed) |
| Increase depth of field (foreground and background both in focus) | Increase aperture i.e. f-number |
Optical Fibres
- Optical fibres are glass or plastic fibre that carries light
-
Advantages include
- low signal loss
- immunity from electromagnetic interference
- higher bandwidth (data rate)
- low power consumption
- Optical fibres work on the principle of Total Internal Reflection
- Applications include long distance communication, endoscopy, light decorations etc
Important particle physics labs
| Facility | Location | Established | Famous for | |||
| Brookhaven National Lab | New York | 1947 | World’s first heavy ion collider World’s only polarized proton collider | |||
| Budker Institute of Nuclear Physics | Novosibirsk (Russia) | 1959 | World’s first particle accelerator | |||
| European Organization for Nuclear Research | Geneva | 1954 | World’s largest particle physics lab Birthplace of World Wide Web Large Hadron Collider (LHC) | |||
| German Electron Synchrotron (DESY) | Hamburg | 1959 | ||||
| Fermilab | Chicago | 1967 | Tevatron – world’s second largest particle accelerator | |||
| High Energy Accelerator Research Organization (KEK) | Tsukuba (Japan) | |||||
| SLAC National Accelerator Lab | Stanford University | 1962 | Longest linear accelerator in the world |
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