Scientific laws are asked in almost every general science paper, and always in one of two forms — a law is named and you supply the scientist, or a phenomenon is described and you supply the law. The set is small, it never changes, and most candidates lose these marks only because they revise physics chapters instead of revising the law-to-scientist table. This post gives that table, explains what each law actually says in one line, and ends with previous year questions.
Key Points (Quick Revision)
- Archimedes' Principle — buoyant force equals the weight of fluid displaced
- Pascal's Law — pressure applied to an enclosed fluid is transmitted equally in all directions
- Bernoulli's Principle — where fluid speed increases, its pressure decreases
- Ohm's Law — current is proportional to voltage at constant temperature
- Doppler Effect — apparent change in frequency due to relative motion
1. Laws of motion and mechanics
| Law or principle | Scientist | What it states |
|---|---|---|
| First Law of Motion | Isaac Newton | A body stays at rest or in uniform motion unless acted on by an external force |
| Second Law of Motion | Isaac Newton | Force equals rate of change of momentum |
| Third Law of Motion | Isaac Newton | Every action has an equal and opposite reaction |
| Law of Universal Gravitation | Isaac Newton | Every mass attracts every other mass |
| Law of Conservation of Momentum | — | Total momentum of an isolated system stays constant |
| Hooke's Law | Robert Hooke | Within the elastic limit, stress is proportional to strain |
| Kepler's Laws | Johannes Kepler | Three laws describing planetary orbits around the Sun |
The first law is also called the law of inertia, and exams use that name as often as the number. The examples attached to it are the standard ones — a passenger lurching forward when a bus brakes, dust leaving a beaten carpet. The third law is asked through examples too: the recoil of a gun, the motion of a rocket, and walking.
2. Laws of fluids and pressure
| Principle | Scientist | Everyday application |
|---|---|---|
| Archimedes' Principle | Archimedes | Floating of ships; submarines; the hydrometer |
| Pascal's Law | Blaise Pascal | Hydraulic lift, hydraulic brakes, hydraulic press |
| Bernoulli's Principle | Daniel Bernoulli | Aircraft lift; the spin of a cricket ball; an atomiser |
| Boyle's Law | Robert Boyle | At constant temperature, pressure is inversely proportional to volume |
| Charles's Law | Jacques Charles | At constant pressure, volume is proportional to absolute temperature |
| Avogadro's Law | Amedeo Avogadro | Equal volumes of gases contain equal numbers of molecules |
| Graham's Law | Thomas Graham | Rate of diffusion is inversely proportional to the square root of density |
Three of these are asked through applications rather than statements. Pascal's Law is the hydraulic answer — brakes, lift, press. Bernoulli's Principle is the aerofoil answer — aircraft lift and the swing of a ball. Archimedes' Principle is the floating answer. If you fix those three application-to-principle links, most fluid questions resolve immediately.
Boyle's and Charles's laws are confused constantly because both involve gases. The separation is simple: Boyle holds temperature constant and links pressure to volume; Charles holds pressure constant and links volume to temperature.
3. Laws of electricity, magnetism and light
| Law | Scientist | What it states |
|---|---|---|
| Ohm's Law | Georg Ohm | Current is proportional to potential difference at constant temperature |
| Coulomb's Law | Charles-Augustin de Coulomb | Force between two charges varies inversely with the square of the distance |
| Faraday's Laws of Electromagnetic Induction | Michael Faraday | A changing magnetic field induces an electromotive force |
| Lenz's Law | Heinrich Lenz | Induced current opposes the change that produced it |
| Fleming's Left Hand Rule | John Ambrose Fleming | Direction of force on a current-carrying conductor in a magnetic field |
| Fleming's Right Hand Rule | John Ambrose Fleming | Direction of induced current in a moving conductor |
| Joule's Law of Heating | James Prescott Joule | Heat produced is proportional to the square of the current |
| Snell's Law | Willebrord Snell | Relates angles of incidence and refraction at a boundary |
The two Fleming rules are the classic trap. The way to hold them apart is by machine: the left hand rule applies to the motor, where current produces motion, and the right hand rule applies to the generator, where motion produces current. Lenz's Law is asked as the conservation-of-energy statement behind induction.
4. Laws of thermodynamics and chemistry
| Law | What it states |
|---|---|
| Zeroth Law of Thermodynamics | Two systems each in thermal equilibrium with a third are in equilibrium with each other |
| First Law of Thermodynamics | Energy can be neither created nor destroyed, only converted |
| Second Law of Thermodynamics | Heat flows spontaneously from a hotter to a colder body; entropy of an isolated system increases |
| Law of Conservation of Mass | Mass is neither created nor destroyed in a chemical reaction — Antoine Lavoisier |
| Law of Definite Proportions | A compound always contains the same elements in the same proportion by mass — Joseph Proust |
| Law of Multiple Proportions | Masses combining with a fixed mass of another element are in simple whole-number ratios — John Dalton |
| Le Chatelier's Principle | A system at equilibrium shifts to counteract an imposed change |
The first law of thermodynamics and the law of conservation of energy are the same statement in different words, and exams use both phrasings. The Zeroth Law is the basis of the thermometer, which is the application questions attach to it.
5. Other principles that appear regularly
| Principle | Scientist | Note |
|---|---|---|
| Doppler Effect | Christian Doppler | Change in apparent frequency due to relative motion; used in radar and to study receding galaxies |
| Heisenberg's Uncertainty Principle | Werner Heisenberg | Position and momentum cannot both be known exactly |
| Photoelectric Effect | Albert Einstein | Emission of electrons when light of sufficient frequency strikes a metal |
| Pauli Exclusion Principle | Wolfgang Pauli | No two electrons in an atom can have the same set of quantum numbers |
| Raman Effect | C. V. Raman | Scattering of light with a change in wavelength; Nobel Prize in Physics, 1930 |
| Tyndall Effect | John Tyndall | Scattering of light by colloidal particles |
| Bohr's Model | Niels Bohr | Electrons occupy fixed energy levels around the nucleus |
The Raman Effect deserves separate attention because it carries an Indian-science question attached to it: C. V. Raman received the Nobel Prize in Physics in 1930, and National Science Day is observed on 28 February to mark the discovery. That single entry answers questions in three different topics.
6. Application to law — the reverse table
Questions increasingly give the application rather than the name. This table runs the other way.
| Application | Law or principle |
|---|---|
| Hydraulic brakes and hydraulic lift | Pascal's Law |
| Lift of an aircraft wing | Bernoulli's Principle |
| Floating of a ship; the hydrometer | Archimedes' Principle |
| Working of an electric motor | Fleming's Left Hand Rule |
| Working of a generator or dynamo | Fleming's Right Hand Rule |
| Recoil of a gun; motion of a rocket | Newton's Third Law |
| Passenger lurching when a bus stops | Newton's First Law (inertia) |
| Heating in an electric iron or heater | Joule's Law of Heating |
| Changing pitch of an approaching siren | Doppler Effect |
| Visible beam of light in a dusty room | Tyndall Effect |
| Basis of the thermometer | Zeroth Law of Thermodynamics |
7. Previous year questions
- Hydraulic brakes work on which principle? — Pascal's Law
- The lift of an aircraft wing is explained by which principle? — Bernoulli's Principle
- Which principle explains the floating of ships? — Archimedes' Principle
- Ohm's Law relates current to which quantity? — Potential difference
- Which rule gives the direction of force in an electric motor? — Fleming's Left Hand Rule
- Which rule applies to a generator? — Fleming's Right Hand Rule
- The recoil of a gun illustrates which law? — Newton's Third Law of Motion
- Newton's First Law is also known as the law of what? — Inertia
- At constant temperature, pressure and volume of a gas are related by which law? — Boyle's Law
- The change in pitch of an approaching siren is due to which effect? — Doppler Effect
- C. V. Raman won the Nobel Prize for which discovery? — Raman Effect
- Which effect explains the scattering of light by colloidal particles? — Tyndall Effect
- The law of conservation of mass was given by which scientist? — Antoine Lavoisier
- Which principle states that position and momentum cannot both be known exactly? — Heisenberg's Uncertainty Principle
- Heat produced in a conductor is proportional to the square of the current — which law? — Joule's Law of Heating
8. Frequently Asked Questions
What is the difference between Boyle's Law and Charles's Law?
Boyle's Law keeps temperature constant and states that pressure is inversely proportional to volume. Charles's Law keeps pressure constant and states that volume is proportional to absolute temperature. Both are gas laws, which is why they appear as options against each other.
How do I remember Fleming's left and right hand rules?
By machine rather than by hand. The left hand rule applies to the motor, where current produces motion. The right hand rule applies to the generator, where motion produces current. Once you fix motor with left and generator with right, the direction questions follow.
Which law explains the working of a hydraulic lift?
Pascal's Law, which states that pressure applied to an enclosed fluid is transmitted equally in all directions. The same law explains hydraulic brakes and the hydraulic press, and all three appear as separate questions.
Are Newton's First Law and the law of inertia the same?
Yes. They are two names for the same statement — a body continues at rest or in uniform motion unless acted on by an external force. Exams use both names, so recognise either.
Which Indian scientist has a scientific effect named after him?
C. V. Raman, for the Raman Effect, the scattering of light with a change in wavelength. He received the Nobel Prize in Physics in 1930, and National Science Day is observed on 28 February to mark the discovery.
For more General Science topics in simple language, see our Newton's Laws of Motion and Scientific Instruments and their Uses posts, or browse the General Science section. Preparing for a specific exam? Start with the SSC CGL guide or join the 100 Hour GS Course.