Physics
🔒 Log in to trackNuclear physics, inventions and scientists
🔒 Log in to trackNuclear physics
- Radioactivity discovered by Henri Becquerel (1896); Marie and Pierre Curie discovered polonium and radium.
- Alpha (helium nucleus) — least penetrating; beta (electrons); gamma (EM waves) — most penetrating.
- Carbon-14 dating (W.F. Libby) estimates the age of fossils and ancient organic remains.
- Nuclear fission — a heavy nucleus (e.g. U-235) splits on neutron capture → atom bomb, nuclear power reactors. Nuclear fusion — light nuclei (hydrogen isotopes) join → energy of the Sun and stars, hydrogen bomb.
- Mass–energy equivalence E = mc² (Einstein).
- In a reactor: moderator slows neutrons (heavy water, graphite); control rods absorb neutrons (cadmium, boron); coolant (water, liquid sodium).
- India: Apsara (1956, Trombay) — first research reactor in Asia; Tarapur (1969) — first nuclear power station. Homi J. Bhabha — father of India's nuclear programme; Vikram Sarabhai — father of India's space programme.
Inventions and discoveries
| Invention / discovery | Person |
|---|---|
| Laws of motion, gravitation | Isaac Newton |
| Telescope (astronomical use), thermometer (thermoscope) | Galileo Galilei |
| Barometer | Evangelista Torricelli |
| Improved steam engine | James Watt |
| Electromagnetic induction, dynamo | Michael Faraday |
| Telephone | Alexander Graham Bell |
| Electric bulb, phonograph | Thomas Edison |
| Radio (wireless telegraphy) | Guglielmo Marconi (J.C. Bose did pioneering microwave work) |
| Television | John Logie Baird |
| X-rays | Wilhelm Röntgen (first Physics Nobel, 1901) |
| Electron | J.J. Thomson |
| Nucleus (gold-foil experiment) | Ernest Rutherford |
| Neutron | James Chadwick (1932) |
| Theory of relativity, photoelectric effect | Albert Einstein (Nobel 1921 for the photoelectric effect) |
| Aeroplane (1903) | Wright brothers |
| Laser (1960) | Theodore Maiman |
| Dynamite | Alfred Nobel |
| Crescograph (plant growth) | J.C. Bose |
| Raman effect | C.V. Raman (Nobel 1930) |
| Chandrasekhar limit | S. Chandrasekhar (Nobel 1983) |
| Bose–Einstein statistics ('boson') | Satyendra Nath Bose |
Inside the atom
An atom has a tiny dense nucleus (protons + neutrons) with electrons moving around it. The particles were found one by one:
- Electron — negative charge, found by J.J. Thomson (1897) in cathode-ray experiments.
- Proton — positive charge, seen in canal rays by E. Goldstein.
- Neutron — no charge, discovered by James Chadwick (1932).
- Nucleus — shown by Rutherford's gold-foil experiment (1911): most alpha particles passed straight through, a few bounced back, so nearly all mass and positive charge sit in a tiny centre. Bohr (1913) added fixed orbits for electrons.
Radioactivity
Henri Becquerel (1896) discovered that uranium salts give out invisible penetrating rays — radioactivity, a property of heavy unstable nuclei. Marie and Pierre Curie discovered polonium and radium; Marie Curie won Nobel Prizes in both Physics (1903) and Chemistry (1911) — the only person with Nobels in two different sciences. The alpha ray is a helium nucleus (least penetrating, stopped by paper), beta is a fast electron (stopped by aluminium), and gamma is an electromagnetic wave (most penetrating, needs thick lead). A Geiger–Müller counter detects radiation. Willard Libby's carbon-14 dating finds the age of old organic remains from the C-14 left in them.
Fission, fusion and reactors
- Nuclear fission: a heavy nucleus such as U-235 splits into two smaller nuclei when hit by a neutron, releasing energy and more neutrons — a chain reaction. Uncontrolled → atom bomb (Hiroshima, 1945). Controlled in reactors → electricity.
- Nuclear fusion: two light nuclei (hydrogen isotopes) join into a heavier one — this powers the Sun and stars, and the hydrogen bomb (far more destructive than a fission bomb).
- Both follow Einstein's E = mc²: a little lost mass becomes a lot of energy.
- In a reactor: the moderator (heavy water, graphite) slows neutrons, control rods (cadmium, boron) absorb neutrons to control the chain reaction, and a coolant carries the heat away. Reactors use fission, not fusion.
India's atomic and space programmes
Homi J. Bhabha is the father of India's nuclear programme; he set up the Tata Institute of Fundamental Research (1945) and BARC at Trombay. Apsara (1956) was India's (and Asia's) first research reactor; Tarapur in Maharashtra (1969) is India's first nuclear power station. India's first nuclear test was at Pokhran in 1974 ("Smiling Buddha"); Pokhran-II followed in May 1998. In space, Vikram Sarabhai is the father of the Indian space programme and ISRO was formed in 1969. Aryabhata (1975) was the first Indian satellite. Chandrayaan-1 (2008) found water molecules on the Moon; Mangalyaan (Mars Orbiter Mission, 2013) made India the first country to reach Mars orbit in its first attempt; Chandrayaan-3 (23 August 2023) made India the first nation to soft-land near the Moon's south pole — the date is now National Space Day. Aditya-L1 (2023) is India's first solar mission. Rakesh Sharma (1984) was the first Indian in space; Shubhanshu Shukla (2025, Axiom-4) the first Indian to visit the International Space Station.
Inventions — who did what
| Invention / discovery | Person |
|---|---|
| Laws of motion, gravitation | Newton |
| Astronomical telescope | Galileo |
| Barometer | Torricelli |
| Improved steam engine | James Watt |
| Electromagnetic induction, dynamo | Michael Faraday |
| Telephone | Alexander Graham Bell |
| Electric bulb, phonograph | Thomas Edison |
| Radio (wireless) | Guglielmo Marconi |
| Television | John Logie Baird |
| Telegraph | Samuel Morse |
| Aeroplane | Wright brothers (1903) |
| X-rays | Wilhelm Röntgen (first Physics Nobel, 1901) |
| Laser (first working, ruby) | Theodore Maiman (1960) |
| A laser gives an intense beam of one wavelength, in step (coherent) — used in surgery, barcode scanners, CD/DVD players and optical-fibre communication. At CERN's Large Hadron Collider (2012) scientists found the Higgs boson, the "God particle" that explains why other particles have mass. |
Question types you will see
Each type: how to recognise it, the method step by step, and one question to try.
Particle or ray ↔ discoverer
'Who discovered the neutron/electron/proton/X-rays/radioactivity/nucleus?' or a match-the-column of particles and scientists.
Particles: electron–J.J. Thomson, proton–E. Goldstein (canal rays), neutron–James Chadwick, nucleus–Rutherford.
Rays: X-rays–Röntgen, radioactivity–Becquerel, radium–Curies.
Models: gold-foil experiment–Rutherford, orbits–Bohr.
each name is fixed by history, so only recall plus elimination works.
The canal rays that led to the discovery of the proton were observed by —
Show solutionHide solution
E. Goldstein. J.J. Thomson found the electron in cathode rays; Chadwick found the neutron in 1932.
Device ↔ inventor
'Who invented the telephone/television/radio/electric bulb/dynamo/steam engine/aeroplane?'
Bell–telephone, Baird–television, Marconi–radio, Edison–bulb and phonograph, Morse–telegraph.
Faraday–electromagnetic induction and dynamo, Watt–improved steam engine, Wright brothers–aeroplane (1903), Galileo–astronomical telescope, Torricelli–barometer.
Eliminate near-names: J.C. Bose did pioneering radio/microwave work but wireless telegraphy's exam answer is Marconi.
The television was invented by —
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John Logie Baird (first public demonstration, 1926). Telephone–Bell, radio–Marconi.
Radioactivity and alpha/beta/gamma
'Which radiation has the most penetrating power?', 'an alpha particle is …', who discovered radioactivity, which instrument detects radiation.
Radioactivity–Becquerel (1896); radium and polonium–the Curies.
α = helium nucleus (2 protons + 2 neutrons), stopped by paper; β = fast electron; γ = electromagnetic wave, most penetrating.
Detection: Geiger–Müller counter. Dating of old remains: carbon-14 (Libby).
An alpha (α) particle is identical to —
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A helium nucleus — 2 protons and 2 neutrons, no electrons.
Fission vs fusion; reactor parts
'The Sun's energy comes from…', 'an atom bomb works on…', 'control rods are made of…', difference between the two bombs.
Heavy nucleus splits → fission (reactors, atom bomb).
Light nuclei join → fusion (Sun and stars, hydrogen bomb).
Reactor parts: moderator slows neutrons (heavy water/graphite); control rods absorb them (cadmium/boron); coolant removes heat.
both processes follow E = mc², but the size of the nucleus tells you which one it is.
The energy of the Sun and stars is due to —
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Nuclear fusion — hydrogen nuclei join into helium at enormous temperature and pressure, releasing energy per E = mc².
India's atomic and space milestones
First reactor/power station/satellite/Mars or Moon mission, fathers of the two programmes, Pokhran tests, National Space Day.
Atomic: Bhabha (father), Apsara 1956 (first research reactor), Tarapur 1969 (first power station), Pokhran 1974 and 1998.
Space: Sarabhai (father), ISRO 1969, Aryabhata 1975 (first satellite), Chandrayaan-1 2008, Mangalyaan 2013 (Mars orbit, first attempt), Chandrayaan-3 south-pole landing on 23 Aug 2023 (National Space Day), Aditya-L1 solar mission.
Persons: Rakesh Sharma first Indian in space (1984); Shubhanshu Shukla first Indian on the ISS (2025).
India's first nuclear power station was set up at —
Show solutionHide solution
Tarapur, Maharashtra (1969). Apsara (1956, Trombay) was the first research reactor.
Modern physics miscellany
E = mc², the 'God particle', laser properties, carbon dating, first Nobels — one-line fact questions from modern physics.
E = mc² — Einstein: mass can convert into energy; the base of both fission and fusion.
Higgs boson ('God particle') — found at CERN's LHC in 2012.
Laser light: one wavelength (monochromatic), in step (coherent), highly directional.
Carbon-14 dating — Willard Libby; ages of fossils and old organic objects.
The 'God particle' whose existence was confirmed at CERN in 2012 is the —
Show solutionHide solution
Higgs boson, predicted by Peter Higgs; it explains how other particles get their mass.
Formula sheet
Einstein
Shortcuts that save time
Fission = split (heavy → lighter, reactors, atom bomb). Fusion = fuse (light → heavier, Sun, hydrogen bomb).
The Sun's energy comes from?
Show solutionHide solution
Nuclear fusion of hydrogen into helium.
Electron — Thomson (1897); nucleus/proton — Rutherford; neutron — Chadwick (1932).
Mistakes to avoid
Where most students lose marks on this subtopic.
Naming Einstein's Nobel for relativity — it was for the photoelectric effect.
Calling the moderator the neutron absorber — control rods (cadmium/boron) absorb; the moderator slows neutrons.
Crediting Edison with the telephone — it was Graham Bell.
Quick revision
Read this the night before the exam.
Electron–Thomson, proton–Goldstein (canal rays), neutron–Chadwick, nucleus–Rutherford, orbits–Bohr.
Radioactivity–Becquerel; radium/polonium–Curies; C-14 dating–Libby; counter–Geiger.
α = helium nucleus, β = electron, γ = EM wave (most penetrating).
Fission = heavy splits (reactor, atom bomb); fusion = light join (Sun, H-bomb); E = mc².
Bhabha (atomic), Sarabhai (space); Apsara 1956, Tarapur 1969, Pokhran 1974/1998.
Aryabhata 1975, Chandrayaan-3 land 23-08-2023, Mars orbit first try 2014.
Practice: 22 questions
Sets of 10, mixed across the question types above. Every answer has a step-by-step explanation.
Topic test · 10 questions
Suggested time 3 min · wrong answers go to your mistake notebook automatically.