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ARCHIMEDE”S PRINCIPLE: When a body is partially or fully immersed in a fluid, it will experience a lost in weight which is equal to the weight of the fluid displaced.

AVOGADRO”S LAW: Equal volume of all gases, at the same temperature and pressure, contain the same number of particles.


The change in energy when electrons move from one energy level to another obeys planck’s equation.

BOYLE’S LAW: The volume of a fixed mass of a gas is inversely proportional to the pressure, provided that the temperature remains constant.

CHARLES’ LAW: The volume of a fixed mass of a gas is directly proportional to the absolute temperature, provided that the pressure remains constant.

CLENCHED FIST RULE (or RIGHT HAND GRIP RULE): If a straight wire is grasped with the right hand so that the thumb points in the direction of the current, then the direction in which the fingers are curled, indicates the direction of the magnetic field.

COULOMB’S LAW: The force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.



FIRST LAW: The mass of the element deposited or liberated at the electrodes during electrolysis is directly proportional to the quantity of electricity that passed through the electrolyte.

SECOND LAW: The masses of different elements deposited or liberated by the same quantity of electricity are directly proportional to the electrochemical equivalents of the element.


FIRST LAW: Whenever there is a change in the magnetic flux linked with a circuit, electromotive force is induced in the circuit.

SECOND LAW: The magnitude of the induced e.m.f is directly proportional to the rate of change of the magnetic flux.

FLEMING’S LEFT HAND RULE: If the left hand is held with the fore finger, the second finger and the thumb mutually at right angles to each other, with the fore-finger pointing in the direction of the magnetic field and the second finger pointing in the direction of the current, then the thumb will point in the direction of the motion or force producing it.

FLEMING’S RIGHT HAND RULE: If the thumb, fore-finger and middle finger of the right hand are held mutually at right angles to each other, with the fore-finger pointing in the direction of the field and the thumb pointing in the direction of motion, then the middle finger will point in the direction of the induced e.m.f or current.

FUNDAMENTAL LAW OF MAGNETISM: Like poles repel while unlike poles attract.

FUNDAMENTAL LAW OF STATIC ELECTRICITY: Like charges repel while unlike charges attract.

HEISENBERG UNCERTAINTY PRINCIPLE (or INDETERMINACY PRINCIPLE): The position and momentum of a particle cannot be determined simultaneously with high degree of accuracy.

HOOKE’S LAW: The extension produced by an elastic material is directly proportional to the applied force provided that the elastic limit is not exceeded. (Also the stress on an elastic material is directly proportional to strain provided that the elastic limit is not exceeded).

JOULE’S LAW: The quantity of heat produced in a given metallic conductor is directly proportional to the product of the resistance of the conductor, square of the current and the time.


FIRST LAW: The planets, each travels along an ellipse with the sun at one focus.

SECOND LAW: The line joining the sun and the planets sweeps out equal areas in equal time.

THIRD LAW: The square of the period of revolution of the planets are proportional to the cubes of their mean distances from the sun.



The particles of gases are in constant random motion and obey Newton’s laws of motion.

As they move, the particles collide with one another and with the walls of their containers.

The diameter of a molecule is small compared with the distance traveled between two successive collisions.

Collisions between molecules occurs in a very short negligible time interval.

When the particles collide with one another and with the walls of the contain momentum is conserved.

The volume of the molecules is a negligible small fraction of the volume occupied by the gas.

The temperature of the gas is a measure of it’s average kinetic energy.

LAW OF CONSERVATION OF ENERGY: Energy can neither be created nor destroyed but can be converted from one form to another.

LAW OF CONSERVATION OF LINEAR MOMENTUM: When two or more bodies on a straight line collide, the total linear momentum before collision is equal to the total linear momentum after collision.


LAW OF REVERSIBILITY OF LIGHT: The path taken by light in its propagation is reversible.


FIRST LAW: the incidence ray, the reflected ray and the normal, at the point of incidence, all lie on the same plane.

SECOND LAW: The angle of incidence is equal to the angle of reflection.


FIRST LAW: The incident ray, the refracted ray and the normal, at the point of incidence, all lie on the same plane.

SECOND LAW (SNELL’S LAW): The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant value for a given pair of media.

LENZ’S LAW: The induced e.m.f in a circuit is in such a direction as to oppose the change producing it.

MAXWELL’S CORKSCREW RULE: If a right handed corkscrew is turned so that its tip travels along the direction of current, the direction of rotation of the corkscrew gives the direction of the magnetic field or magnetic lines of force.

NEWTON’S LAW OF COOLING: The rate of cooling of a body is directly proportional to the temperature difference between the body and its environment.

NEWTON’S LAW OF UNIVERSAL GRAVITATION: Every object in space attracts every other object by a force that is proportional to the product of their masses and inversely proportional to the square of their distance apart.


FIRST LAW: A body will continue in its state of rest or uniform motion on a straight line, unless it is acted upon by a force.

SECOND LAW: The rate of change of momentum is directly proportional to the applied force and it takes place in the direction of force.

THIRD LAW: For every action, there is an equal but opposite reaction.

NUCLEAR THEORY OF ATOM (RUTHERFORD’S ATOMIC MODEL): An atom consists of a centered nucleus which is massive and positively charged (proton). Also at the centre of an atom and as part of the nucleus is another particle with zero charge but with mass equal that of a proton (neutron). Revolving round the nucleus are electrons which are negatively charged with negligible masses.

OHM’S LAW: The current flowing through a metallic conductor is directly proportional to the potential difference across the terminals of the conductor, provided that temperature and all other physical quantities remain constant.

PARALLELOGRAM LAW OF VECTOR ADDITION: If two vectors are represented in magnitude and direction by the adjacent sides of a parallelogram, the diagonal of the parallelogram drawn from the point of intersection of the vectors represents the resultant vector in magnitude and direction.

PASCAL’S PRINCIPLE: The pressure applied to an enclosed fluid is transmitted undiminished to every portion of the fluid and the walls of the containing vessel.

PRESSURE LAW: (Also, GAY-LUSAC’S PRESSURE LAW) The pressure of a fixed volume of a gas is directly proportional to the absolute temperature.

PRINCIPLE OF CONSERVATION OF MECHANICAL ENERGY: In a closed system, the total mechanical energy is always conserved, it can only be changed from one form to another.

PRINCIPLE OF FLOTATION: A body will float in a fluid if it is able to displace its own volume of the fluid.

PRINCIPLE OF MOMENT: If a body is in equilibrium, the sum of clockwise moment about any point on the body is equal to the sum of anticlockwise moment about the same point

PRINCIPLE OF SUPERPOSITION: When two or more disturbances are simultaneously present in the same medium, the displacement caused by each disturbance is the same as it produces when it acts alone.

QUANTUM THEORY OF LIGHT: Light exhibits particulate nature. The particles have quantum energy or photon which is directly proportional to the frequency of light waves. E-hv, where E = photon energy, h=Planck’ constant = 6;63 x 1014 Js. V = frequency.

RIGHT HAND GRIP RULE: See Clenched Fist Rule.

RUTHERFORD’S LAW OF ARTIFICIAL TRANSMUTATION: If an atom gains an alpha particle during nuclear transmutation, it will change to the atom of an element two-step after it in the periodic table and if it gains a beta particle, it will change to the atom of an element a step before it in the periodic table.

SNELL’S LAW: Second law of reflection. See Laws of reflection.

SOUND INVERSE SQUARE LAW: The intensity of energy carried by a wave is inversely proportional to the square of the distance the wave has travelled.

TRIANGLE LAW OF VECTOR ADDITION: If two vectors are represented in magnitude and direction by two sides of a triangle taken in order, the resultant vector is represented in magnitude by the third side.


An atom consists of an inner nucleus around which are some energy levels (shells).

Each energy level contains one or more sub energy levels (orbitals) where electrons can be found.

The electrons in the orbitals show some properties of waves.

The distribution of the electrons in the orbitals depends on the number and kind of energy level occupied.





ABSCISSA: The horizontal coordinate of a point in a two dimensional rectangular Cartesian coordinate system. It can as well refer to the horizontal axis (x-axis). Compare Ordinate

ABSCISSA AXIS: The horizontal axis (x-axis) of a two dimensional graph.


ABSOLUTE HUMIDITY: Mass of water vapour in a unit volume of air in the atmosphere.

ABSOLUTE TEMPERATURE SCALE: Also Thermodynamics Scale, Kelvin Scale. Temperature measuring scale which measures temperature in Kelvin and fixes the triple point of water (i.e the temperature at which water exists simultaneously as solid, liquid and gas) as 273.16 Kelvin (K). On this scale, the freezing point of water (0oC) corresponds to 273.15K and the boiling point of water (100oC) corresponds to 373.15K. One Kelvin change in temperature is equivalent to one degree Celsius change. And T (K) = t (oC) + 273.15

ABSOLUTE TEMPERATURE: Temperature measured in Kelvin temperature scale (K).

ABSOLUTE ZERO TEMPERATURE: The temperature at which a gas volume is zero on a temperature-volume curve. Numerically 0K (-273oC)


ACCELERATION: 1. (Linear) The rate of change of velocity with time. The ratio of the change in velocity to the time taken. It is a vector quantity and is measured in m/s2. If the velocity changes by equal amount in equal time interval the acceleration is called UNIFORM ACCELERATION.

ACCELERATION DUE TO GRAVITY: Also Acceleration of Free Fall Due to Gravity. The rate of change of the velocity of an object falling under the influence of gravity alone. The acceleration of a body due to the gravitational force. The force acting on a unit mass on the earth’s surface.


ACCELERATION OF FREE FALL: See Acceleration Due to Gravity.

ACCEPTOR ELEMENT: (of a semiconductor) See Semiconductor.

AC CIRCUIT: An electric circuit in which alternating current flows. See Electric Circuit, Alternating Current.

ACCOMMODATION: (of an eye) Ability of the eye to alter its focal length in order to focus images at varying distances.

ACCUMAULATOR: See Secondary Cell.

ACHROMATIC LENS: A lens that deviates light ray but does not disperse it. It is produced by combining two lenses of which the dispersion of one is equal and opposite to that of the other, hence no separartion of light into colours occurs. See Chromatic aberration.

ACHROMATIC PRISM: A prism that deviates light rays without separating it into spectrum.

ACOUSTIC RESONANCE: Resonance caused by sound vibration. See Resonance.

ACOUSTICAL PROPERTY: Property related to sound.

ACOUSTICS: The science of sound.

ACTION AND REACTION FORCES: (From Newton’s law) Whenever a force acts on a body, there is always an equal force acting back in opposite direction. The force acting on the body is called the ACTION FORCE and the force acting back in opposite direction is called the REACTION FORCE. Action and reaction are equal but opposite. See Newton’s Laws of Motion.

ACTIVITY: (of a radioactive element) The number of disintegrations of a radioactive element per second until a stable nucleus is formed.

ACTIVITY SERIES: (of element) Arrangement of elements in order of their increasing reactivity.

ADDITIVE COLOUR MIXING: Mixing of coloured light to obtain another coloured light. In additive colour mixing, combination of red and blue colours gives magenta, combination of blue and green gives cyan, combination of green and red gives yellow and combination of red, blue and green gives white. Compare Subtractive Colour Mixing. See Colour Triangle.

ADHESION: Force of attraction between molecules of different substances. Compare Cohesion.

ADIABATIC PROCESS: A process in which there is no exchange of heat between the substance and its environment.

AIR COLUMN: Air confined into a tube.

AIR: A mixture of gases consisting 78% nitrogen, 20.8% oxygen, 1% noble gases, 0.03% carbon di oxide and some water vapour by volume.

ALLOY: A mixture of two or more elements in which the major element (called base element) is a metal and the other (called alloying element) may be a metal or a non metal. Common alloys are

ALNICO: Alloy of (25%) iron, (20-30%) nickel, (5-35%) copper and (about 15%) aluminium. It is used for making magnets.

ALUMINIUM BRONZE: Alloy of aluminium and copper used in construction of aircraft’s part.

BALL BEARING METAL: Alloy of 82% tin, 14% lead and 4%copper used in locomotives.

BRASS: Alloy containing 60-80% copper and 20-40% zinc. It is used for making casting, ornamental objects, nuts and bolts.

BRONZE: Alloy containing 80-90% copper and 10-20% tin. It is used for casting and engraving, sculptural works, coins and medals.

DURALUMIN: Alloy of aluminium with 3% copper, 1% magnesium and 1%manganese. It is used extensively for construction of aircraft, ships and cars.

MAGNALUM: Alloy of aluminium and magnesium used in construction of aircraft’s parts.

PERMALLORY: Alloy containing about 20% iron and 80% nickel used in making electromagnets.

SILVER COIN: Alloy of aluminium, copper and nickel.

SOLDER: Alloy of lead, tin and antimony. It is used for welding, printing and plumbing work. SOFT SOLDER contains eutectic lead-tin alloy while HARD SOLDER (also called BRAZING METAL) is a low melting metal.

STEEL: An alloy of iron and carbon. Stainless steel if (10-20%) chromium, (10-20%) nickel and (less than 0.4%) carbon are added. Hard steel if the carbon percentage is relatively high, nickel is absent and chromium reduced. Steels have wide range of application which include its use for construction of bridges and machinery, surgery equipment and house utensils.

TYPE METAL: Alloy of 75% tin and 25% lead.

ALNICO: See Alloy

ALPHA PARTICLE: A radioactive ray, consisting of fast traveling stream of particles each consisting of two protons and two neutrons and carrying two positive charges. It has atomic number of two, mass number of four, high ionization power, low penetrating power (can be stopped by a sheet of paper) and move with the speed of about 1.5 x 107m/s. they are slightly deflected by strong electromagnetic fields towards the negative side. Compare Beta Particle, Gamma Ray.

ALPHA RAY: See Alpha Particle

ALTERNATING CURRENT: An electric current that varies in such a way as to reverse its direction periodically.

ALTIMETER: An instrument used for measuring the altitude (height above sea level) of a place. It is usually an aneroid barometer graduated with a height scale.


AMALGAMATION: Act of coating the surface of a metal (usually zinc) with mercury. It is used to prevent local action in electrochemical cells. See Cell, Local Action.

AMMETER: Instrument used for measuring electric current. See Electric Current. Compare Galvanometer.

AMORPHOUS SUBSTANCE: Also Non Crystalline Substance. A Substance with particles not arranged in a regular repetitive pattern. Compare Crystalline substance.

AMPERE: Unit of electric current. It is a fundamental units and expressed as A. The current is one Ampere if one coulomb of electric charges passes through a conductor in one second.

AMPLIFIER: A device used to increase the amplitude of a wave.

AMPLITUDE: 1. (of a wave). The maximum displacement of a wave from its mean position. 2 (of a simple harmonic motion) The maximum displacement of a body performing Simple Harmonic Motion from its mean position. See Simple Harmonic Motion.


ANGLE OF DECLINATION: Also called Angle of Variation or Angle of Deviation. The angle between a free horizontal compass needle (magnetic north) and the true geographic north, i.e. the angle between the magnetic north and the vertical. Compare angle of Dip

ANGLE OF DEVIATION: 1. (of light) The angle between the incident ray and the emergent ray of light in a prism. Angle at which a light ray is deviated in a prism. Minimum deviation occurs in a prism when the angle at which the ray enters one face is equal to the angle at which it leaves the opposite face. 2. (of earth magnetism) See Angle of Declination.

ANGLE OF DIP: Also Angle of Inclination. Angle between the free magnetic needle and the horizontal plane. Compare Angle of Declination.

ANGLE OF EMERGENCE: The angle which a ray of light coming out from a medium makes with the normal (a line drawn perpendicularly to the surface of the medium at the point of emergence).

ANGLE OF INCIDENCE: The angle at which a wave (usually light ray) travelling from one medium to another enters a medium when measured with reference to a line drawn perpendicularly to the boundary between the two media (normal) at the point it enters the medium.





ANGLE OF REPOSE: (of an inclined plane) The maximum angle of inclination to the horizontal at which an object on an inclined plane can remain at rest.

ANGLE OF VARIATION: See Angle of Declination.


ANGULAR DISPLACEMENT: The angle turned through by a body undergoing rotational motion.

ANGULAR DISTANCE: See Angular displacement

ANGULAR MAGNIFICATION: (of a microscope) The ratio of the angle subtended at the eye by the image formed by the microscope to the angle subtended by the object when it is at the point of most distinct vision


ANGULAR MOMENTUM: The product of the moment of inertia of a body and its angular velocity for a body undergoing a rotational motion.



ANION: See Ion.


ANODE: A positive electrode in an electrolytic cell or a negative electrode in an electrochemical cell, through which electrons enter the circuit and on which anions are deposited during electrolysis. Oxidation takes place at the anode. See Electrolysis, Electrode, Cell, Anion. Compare Cathode.

ANOMALOUS EXPANSION: Irregular expansion of a substance when heated. ANOMALOUS EXPANSION OF WATER refers to the irregular expansion of water when heated. When water is heated from 0oC to 4oC it contracts rather than expanding but starts expanding from 4oC to 100oC, hence having its lowest volume and highest density at 4oC.

ANTINODAL LINE: A line of constructive interference observed when two circular waves are superposed in the same phase.

ANTINODE: (of a wave) The point of maximum displacement of the particles of a stationary wave. Compare Node. See Stationary Wave.

APERTURE: See Mirror


APPARENT DEPTH: Usually used to describe the depth of a body when viewed from another medium due to the refraction of light in the medium. The apparent depth is smaller than real depth if a dense medium is viewed from a less dense medium.

APPARENT DISPLACEMENT: The difference between the real depth and the apparent depth. See Apparent depth.

ARCHIMEDE: Archimedes of Syracuse ( 287 BC – 212 BC) A Greek mathematician, physicist, engineer, inventor, and astronomer. Among his advances in physics are the foundations of hydrostatics, statics and an explanation of the principle of the lever. He is credited with designing innovative machines, including siege engines and the screw pump. in his treatise “On Floating Bodies”, Archimeds described the principle of upthrust which is known today as Archimede’s principle. He also gave the law of flotation. The most widely known anecdote about Archimedes tells of how he invented a method for determining the volume of an object with an irregular shape. A crown had been made for King Hiero II, who had supplied the pure gold to be used, and Archimedes was asked to determine whether some silver had been substituted by the dishonest goldsmith. Archimedes had to solve the problem without damaging the crown, so he could not melt it down into a regularly shaped body in order to calculate its density. While taking a bath, he noticed that the level of the water in the tub rose as he got in, and realized that this effect could be used to determine the volume of the crown. For practical purposes water is incompressible, so the submerged crown would displace an amount of water equal to its own volume. By dividing the mass of the crown by the volume of water displaced, the density of the crown could be obtained. This density would be lower than that of gold if cheaper and less dense metals had been added. Archimedes then took to the streets naked, so excited by his discovery that he had forgotten to dress, crying “Eureka!” (Greek: “εὕρηκα!,”meaning “I have found it!”). The test was conducted successfully, proving that silver had indeed been mixed in.

ARCHIMEDES PRINCIPLE: See Laws, Theories and Principles.

AREA EXPANSION: Also Superficial Expansion. Increase in area when a body is heated. See also Linear Expansion, Cubic expansion

AREA EXPANSIVITY: Also Superficial Expansivity. Coefficient of area expansion. Increase in area per unit area for each degree rise in temperature. Usually denoted as β. It is measured in k-1

ARMATURE: A moving part of an electric motor or generator

ARTIFICIAL NUCLEAR TRANSMUTATION: Process of changing an element into another element by bombarding it with radioactive rays.



ASTEROID: Small rocky body usually moving along circular orbits between Mars and Jupiter. They are believed to be formed from planetary bodies that have broken up long time ago.

ASTHENOSPHERE: Layer of the earth after the lithosphere. It is made up of molten materials.

ASTRONAUT: Space traveler. A researcher that travels to the space.



ATMOSPHERE: The gaseous part of the earth.

ATMOSPHERIC PRESSURE: The pressure exerted by the atmospheric air on the surface of the earth. One atmospheric pressure (atm) is equivalent to 105 N/m2 or 760mmHg

ATOM: The smallest part of an element that can retain the chemical property of the element. The smallest part of an element that can take part in a chemical reaction. An atom consists of an inner part called the NUCLEUS and an outer part called SHELL or ORBIT. A typical atom consists of three particles generally called SUBATOMIC PARTICLES. They are the PROTONS which are located in the nucleus, carrying positive charges (each of magnitude 1.602 X 10-19) and having relative mass of 1 each (real mass of about 1.67 X 10-27Kg), The NEUTRONS which are also located in the nucleus, have no electric charge and a relative mass of 1 (real mass of about 1.67 X 10-27Kg) and the ELECTRONS which are found constantly revolving round the shells, carrying negative charges (each of magnitude 1.602 X 10-19) and have relative mass of 1/1850 each (real mass of about 9.11 X 10-31Kg). Particles found inside the nucleus (the protons and the neutrons) are called the NUCLEON.

ATOMIC BOMB: Also Fission Bomb: A nuclear weapon designed to explode. Usually used as a weapon in military campaign. It releases energy through nuclear fission.

ATOMIC ENERGY LEVEL: Any of the orbital of energy where electrons can be found.


ATOMIC MASS: See Relative Atomic Mass.

ATOMIC MODEL: See Bohr’s Atomic Model, Rutherford’s Atomic Model, Electron Cloud Model.

ATOMIC NUMBER: The number of protons present in the nucleus of the atom of an element. It is also the same as the number of electrons present in the atom of the element if the atom is electrically neutral.

ATOMIC REACTOR: See Nuclear reactor

ATTENUATION: Loss in power by an electromagnetic wave passing through a medium due to the absorption of the wave energy by the medium.

AUDIOMETER: See Sonometer

AUTOTRANSFORMER: A kind of transformer that uses the same coil as both primary coil and secondary coil.

AVOGADRO’S CONSTANT: Also Avogadro’s number. Number of particles (atoms, ions, molecules) contained by one mole of an element. It numerically equals to 6.023 X 1023

AVOGADRO’S NUMBER: See Avogadro’s Constant.

AVOMETER: See Multimeter.




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