• Mon. Jan 18th, 2021



Dear readers, boost up your preparation for SSC CPO and CGL 2016 by this well designed notes for science notes for general awareness portion.


  • Acarology : Branch of zoology dealing with ticks and mites.
  • Acoustics : The study of sound (or the science of sound).
  • Aerodynamics : The branch of mechanics that deals with the motion of air and other gases; the study of the motion and control of solid bodies like aircraft, missiles in air.
  • Aeronautics ; The science or art of flight.
  • Aerostatics : The branch of statics that deals with gases in equilib­rium and with gases and bodies in them.
  • Aetiology : The science of causation.
  • Agrobiology : The science of plant life and plant nutrition.
  • Agrology : Soil science dealing with production of crops.
  • Agronomy : The science of soil management and production of field crops.
  • Agrostology : The study of grasses.
  • Alchemy : Chemistry in ancient times.
  • Anatomy : The science dealing with the structure of animals, plants or human body.
  • Anaesthesiology : Branch of medicine dealing with administration of anaesthetics and the             patient’s condition while under anaesthesia.
  • Anthropology : The Science that deals with the origin and physical and cultural development of mankind.
  • Arboriculture : Cultivation of trees and vegetables.
  • Archaeology : The study of antiquities.
  • Astrochemistry ; Science relating to composition and reaction of sub­stances found in celestial
  • Astrogeology : Dealing with structure and formation of rocks and min­erals found in other
  • Astrology : The ancient art of predicting the course of human desti­nies with the help of          indications deduced from the position and move­ment of the heavenly bodies.
  • Astronautics : The science of space travel.
  • Astronomy ; The study of the heavenly bodies.
  • Astrophysics : The branch of astronomy concerned with the physical nature of heavenly bodies.
  • Bacteriology : The study of bacteria.
  • Biochemistry : The study of chemical processes of living things.
  • Biology : Science dealing with study of living things.
  • Biometry : The application of mathematics to the study of living things.
  • Bionics : The study of functions, characteristics and phenomena ob­served in the living world and                 the application of this knowledge to the world of machines.
  • Bionomics : The study of the relation of an organism to its environ­ment.
  • Bionomy : The science of the laws of life.
  • Biophysics : The physics of vital processes (living things).
  • Botany : The study of plants.
  • Cardiology : A branch of medicine dealing with the heart Carpology : The study of fruits and
  • Cetology : Dealing with the study of aquatic mammals
  • Chemistry : The study of elements and their laws of combination and behaviour.
  • Chemotherapy : The treatment of disease of using chemical substances.
  • Cherology : Study of geographical areas and distribution of plants/ animals.
  • Chxonobiology : The study of duration of life.
  • Chronology : The science of arranging time in periods ascertaining the dates and historical order of past
  • Conchology : The branch of zoology dealing with the cells of molluscs.
  • Cosmogony : The science of the nature of heavenly bodies. Cosmography : The science that                 describes and maps the chain fea­tures of the universe.
  • Cosmology : The science of the nature, origin and story of the uni­verse.
  • Craniology : Hie study of skulls.
  • Criminology : The study of crime and criminals.
  • Cryptography : The study of secret writings.
  • Crystallography : The study of structure, forms and properties of crys­tals.
  • Crybgfenics : The science dealing with the production, control and ap­plication of very low
  • Cytochemsitry : The branch of cytology dealing with chemistry of cells.
  • Cytogenetics : The branch of biology dealing with the body of heredity from the point of view of                 cytology and genetics.
  • Cytology : The study of cells, especially their formation, structure and functions.
  • Cytology : The study of cells, especially their formation, structure and functions.
  • Cytopathology : The study of cells in diseases.
  • Dactylography : The study of fingerprints for the purchase or identifi­cation.
  • Dactylology : The study of fingerprints.
  • Dandrology : Science dealing with study of trees.
  • Dietetics : Science dealing with study of diet and nutrition.
  • Ecology : The study of the relation of animals and ants to their sur­roundings/ animate arid
  • Econometrics : The application of mathematics in testing economic theo­ries.
  • Economics : The science dealing with the production, distribution and consumption of goods and services.
  • Embryology : The study of development of embryos.
  • Endocrinology : The study of endocrine glands and air secretions.
  • Entomology : The study of insects.
  • Epidemiology : The branch of medicine dealing with communicable diseases.
  • Epigraphy : The study of inscriptions.
  • Epistemology : Study of the nature of knowledge.
  • Eschatology : Study of death and destiny.
  • Ethnography : A branch of anthropology dealing with scientific descrip­tion of individual cultures.
  • Ethnology : A branch of anthropology that deals with origin; distribu­tion and distinguishing                      characteristics of races of mankind.
  • Ethology : The study of animal behaviour.
  • Eugenics : The study of the production of better offering by the care­ful selection of parents.
  • Exobiology : Branch of biology relating to the search study of extra­terrestrial living organisms.
  • Gcnecology : The study of genetical composition of plant population in relation to their habitat.
  • Genesiology : The science of generation.
  • Genetics : The branch of biology dealing with the phenomena of he­redity and the laws                                               governing it.
  • Geobiology : The biology of terrestrial life.
  • Geobotany : The branch of botany dealing with all aspects of relations between plants and the                 earth’s surface.
  • Geochemistry : The study of the chemical composition of the earth’s crust and the changes                     which take place within it.
  • Geology : The science that deals with the physical history of the earth.
  • Geomedicine : The branch of medicine dealing with the influence of climate and environmental                 conditions on health.
  • Geomorphology : The study of the characteristics, origin and devel­opment of landforms.
  • Geophysics : The physics of the earth.
  • Geriatrics : Branch of medicine relating to diagnosis and treatment of diseases afflicting the
  • Geriodontics : Dealing with dental problems of the elderly people.
  • Gerontology : The study of old age, its diseases, etc.
  • Gynaecology : Dealing with female diseases of the reproductive sys­tem.
  • Haemetology : Relating to study of blood and blood disorders.
  • Hepatology : Branch of medicine relating to study of liver and its dis­eases-
  • Histology : The study of tissues.
  • Horticulture : The cultivation of flowers, fruits, vegetables and orna­mental plants.
  • Hydrodynamics : The mathematical study of the forces, energy and pressure of liquid in motion.
  • Hydrography : The science of water measurements of the earth with special reference to their              use for navigation.
  • Hydrology : The study of water with reference to its occurrence and properties in the hydrosphere and atmospheres.
  • Hydropathy : The treatment of disease by the internal and external use of water.
  • Hydroponics : The cultivation of plants by placing the roots in liquid nutrient solutions rather than in soil.
  • Hydrostatics : The mathematical study of forces and pressures in liquids.
  • Hygiene : Science of health and its preservation.
  • Hypnology : Study of sleep.
  • Ichthyology : Study of fishes.
  • Immunology : Branch of medicine relating to the immune system in the body.
  • Lalopathology : Branch of medicine relating to study of speech disorders.
  • Lithology : Study of characteristics of rocks.
  • Malacology : Branch of zoology concerned with study of mollusks of shell-bearing organisms.
  • Metallography : Study of the crystalline structures of metals and alloys.
  • Meteorology : Science of the atmosphere and its phenomena.
  • Metrology : Scientific study of weights and measures, bacteria, molds and pathogenic protozoa.
  • Minerology : Study of distribution, identification and properties of min­erals.

SSC CGL Physics Notes: PHYSICS

Physics is the branch of science which is concerned with the study of matter and energy and their inter-relationship. Numerous developments have taken place in the realm of Physics, from the earlier stages of classical phys­ics to the emergence physics based on quantum theory. Classical physics included topics like optics, mechanics, electricity, magnetism, acoustics. In the twentieth century quantum physics has made much headway and it includes topics like atomic, nuclear, particle etc.



Some SI Derived Units
Quantity Name of Unit Symbol
Area square meter
Volume Cubic meter
Frequency hertz Hz
Mass density (density) kilogram per cubic meter kg/
Speed, velocity meter per second m/s
Angular velocity radian per second rad/s
Acceleration meter per second per second m/
Angular Acceleration Radian per second per second rad/
Force Newton N    kg.m/


Pressure pascal Pa
Work, energy, quantity of Heat Joule J             N.m
Power Watt W       J/s



Quantity of electric Charge Coulomb C        A.s
Potential Difference Volt V
Electromotive force Volt W/A
Electric field Strength Volt per meter or Newton per coulomb V/m       N/C
Electric resistance ohm      V/A
Capacitance farad F    A.s/V
Magnetic flux Weber Wb    V.s
Inductance henry H     V.s/A
Magnetic flux density tesla T     wb/
Magnetic field strength Ampere per meter A/m
Entropy Joule per Kelvin J/K
Specific heat Joule per kilogram per Kelvin W/(m.K)
Radiant Intensity Watt per steradian W/sr
Plane angle radian rad
Solid angle steradian sr


SSC CGL Physics Notes



  • Motion is change of position of a body with time.
  • Two types of Motion are, Linear Motion and Rotatory Motion.
  • Scalar quantities : Those physical quantities which are completely de­scribed by a magnitude (size) alone, are known as scalar quantities, e.g. length or distance, mass, time, area, volume,                 work, power, en­ergy, temperature, speed, pressure, charge and potential.
  • Vector quantities : Those physical which are completely described only if their magnitudes as well as directions are known, are called vector quantities, e.g. displacement, velocity,               acceleration, force, weight, moment, momentum and electric field.


  • The distance traveled by a body is the actual length of the path cov­ered by a moving body irrespective of the direction in which the body travels.
  • It is a scalar quantity having magnitude only.


  • When a body moves from one position to another, the shortest dis­tance between the initial position and final position of the body alongwith direction is known as its displacement.
  • Vector quantity have magnitude as well as direction.


  • Speed is the scalar form of velocity. It is defined as the distance trav­eled in one second. If the body covers a distance d in time t, then speed V = d/t


  • If the body covers unequal distance in equal interval of time, then it is said to be moving with a variable speed.
  • Acceleration is always present if the speed of the body is variable.


  • The speed of the body is. uniform if it covers equal distance in equal interval of time.
  • Acceleration may or may riot be there in the motion if the body is mov­ing in uniform speed e.g. a body moving in uniform circular motion has uniform speed but variable velocity therefore                acceleration is present in the circular motion.


  • If a body has travelled and ‘  distance with ‘ and ‘’ velocities,

Then average speed =


  • The rate of change of displacement is called velocity.
  • V =
  • It is a vector quantity.
  • Velocity may be positive and negative.


  • When a body covers equal displacement in equal interval of time the velocity is said to be
  • Acceleration is absent if the body moves with uniform velocity. VARIABLE VELOCITY
  • When a body covers unequal displacement in equal intervals of time then it is said to have variable velocity.
  • Acceleration is necessarily present in this motion.
  • In this case either direction of velocity or magnitude or both change with respect to time e.g. speed is constant in uniform circular motion but velocity is variable.


  • Average velocity is zero If the body returns to starting point in the given time interval.
  • If the body covers first half distance with velocity and next half with

velocity  then the average velocity =

  • If a body travels with uniform velocity for time  and with uniform velocity  for time ,                 then the average velocity is
  • A body whose velocity falls with the passage of time is said to be un­dergoing deceleration or A  retardation may be treated as a negative acceleration.
  • The acceleration of a moving body is the rate of change of its velocity, i.e.,

a =    where ‘a’ is the acceleration, ‘u’ is the initial velocity which becomes ‘ in ‘t’ second


  • Time rate of change in velocity is known as acceleration.
  • It is a vector quantity.
  • Negative acceleration is known as retardation. It indicates that the ve­locity of the object is decreasing with respect to time.



  • If the velocity of the body changes in different amounts during the same time intervals, then the acceleration of the body is known as variable acceleration.
  • Acceleration is variable if either its direction or magnitude or both changes with respect to time, g. acceleration in uniform circular mo­tion.



  • If the velocity of the body changes by same amounts in same intervals of time, then the acceleration of the body is known as uniform accel­eration, g. acceleration due to gravity.


(i)  = u + at, (ii) s = ut +  a                                                          (iii)   =  + 2 a s

Where initial velocity = u                                                Final velocity =

Elapsed time = t                                                                      Acceleration = a

Distance covered = s

  • The acceleration caused by the earth’s attraction is known as the acceleration due to gravity and it is identified by the symbol ‘g’ Mean value of g’ is 9.8 m/.
  • It the body travels downwards, then ‘g’ is positive. However, if the body is projected vertically upwards, then ‘g’ is negative.


  • Newton’s First Law of Motion : Every body continues to be in a state of rest or of uniform motion, unless compelled by an external force to change that state. The first law can be called               law of Inertia.
  • Newton’s Second Law of Motion : The rate of change of momentum is directly proportional to the applied force and takes place in the di­rection in which the force acts. The second law can be               termed as the law of acceleration.
  • Newton’s Third Law of Motion : For every action, there is an equal and opposite reaction.


  • A force is that pull or push which changes or tends to change the state of motion of a body.
  • The tendency of a body to remain in the state it is, either stationary or moving, is called its
  • The more the mass of the objects, the greater is their inertia.
  • The force (F) which causes an acceleration (a) in a moving object of mass (m) is given by F = ma
  • The SI unit of force is Newton.
  • To every action there is always an equal and opposite reaction and ac­tion-reaction forces act on different bodies.


  • The force which a body possesses, due to the combined effect of its mass and velocity is called
  • The greater the mass and velocity of an object, the larger is its mo­mentum.
  • For example, cars are heavy and fast. Thus, they have enough mo­mentum to crumple steel and break down brick walls when they crash to a halt.
  • According to the law of conservation of momentum, in a colliding sys­tem, the total momentum remains conserved.
  • When a force of very large magnitude is applied on a body for a very short interval of time, then collective effect of force and time is called impulse.


  • Gravity is the force which pulls all bodies towards the centre of the earth, keeps the planet revolving round the sun in definite paths and is responsible for the weight of all objects.
  • A falling body accelerates under the influence of gravity.
  • Different masses, fall to the ground together, because acceleration due to gravity is same for all
  • Every particle in the universe attracts every other particle with a force F which depends on the masses ‘m/ and ‘m2’ of the interacting par­ticles and on their separation V. Greater the masses              and smaller the separation, greater is the force of attraction. It is called Gravitational Force.
  • Gravity is a special form of Gravitational Force, in which the interact­ing bodies are the earth and any other object.
  • The value of acceleration due to gravity, i.e., ‘g’ decreases with height and depth.
  • The radius of the earth is slightly more at the equator than at the poles. So, ‘g’ is less at the equator than at the poles. So artificial satellites are launched from the places near or on the


  • Mass is measure of the atoms contained in an object, and the number of atoms in the object remains So, mass is an intrinsic, un­changing property of matter.
  • The force with which a body is attracted towards earth is called weight. W = mg; where ”W is the weight and ‘m’ is the mass.
  • Mass is measured with the help of physical balance, while a spring balance measures the weight of an object.


  • Friction is a kind of force that opposes relative motion.
  • It comes into existence at the common boundary of two bodies in con­tact with one another, when one of them either moves or tends to move relative to the other.
  • Force of friction does not depend on the area of contact.
  • Frictional force increases with weight.
  • On rough surfaces, frictional force is more than that on the smooth surfaces.
  • Less force is needed to maintain motion than to initiate it i.e.. Kinetic friction < Static friction.
  • Kinetic friction does not depend on the speed, when the speed is not large.
  • The vehicles are provided with wheels and their axles are supported with ball bearings, because the rolling friction is much less than the sliding friction.
  • Friction is necessary for the operation of belts, pulleys, clutches and brakes. Nails and screws remain firmly fixed in which they are driven because of friction.
  • For motion in a fluid, the frictional forces that oppose the motion are called drag forces,
  • The drag forces depend on area, shape and the velocity of the moving body. For faster motion, the drag force may be assumed to be propor­tional to the square of the velocity.


  • Static Friction: Frictional force arises on account of the contact of two surfaces. If the surfaces remain at rest, there is static friction.
  • Static friction acts as a resistance to the commencement of relative mo­tion between the two
  • Dynamic Friction: Friction that exists during the relative slipping of one surface over another is called dynamic or kinetic friction.
  • Dynamic friction is less than the Static Friction.
  • Rolling Friction: When a body rolls over a surface the frictional force that develops is known as rolling friction.


  • Work is said to be done only, when a force or its component causes displacement in its own
  • In SI system, unit of work is called Joule.
  • W = F x d; where is the work done, ‘F’ is the force and ‘d’ is the displacement.
  • Rate of doing work is called power. Power (P) can be defined as the product of force (f) and velocity (v).

P = fv

  • In SI system, absolute unit of power is called Joules/second or
  • The capacity of a body to do work is called
  • Energy is the total amount of work done by a body, therefore, its unit is the same as that of
  • Conveniently, energy is divided into (i) potential energy and (ii) kinetic energy.
  • When a body does work by virtue of its motion, it is said to have ki­netic energy. If ‘m’ is the mass of the body, moving with an initial ve­locity v, then its Kinetic Energy (KE) is given by

KE = m

  • A fast moving electron, running water, blowing wind; a speeding car; a shooting arrow etc., have kinetic energy.
  • Electric energy, radiant heat, light energy, mechanical energy can be regarded as kinetic energy.
  • If a body does work by virtue of its position or configuration, it is said to have potential energy.
  • If a body of mass ‘m’ be raised vertically through a height ‘h’ against the acceleration due to gravity ‘g’ then its Potential Energy (PE) is PE = mgh.
  • When a body is on the surface of earth, then the potential energy be­tween the system of body, and the earth is zero.
  • When the body moves vertically upward, the height of the body from ground increases, and hence potential energy between the system of the earth and the body increases.
  • When a body falls towards the earth, the height of the body from ground decreases. Thus the potential energy between the system of the earth and the body decreases.
  • When, the spring of watch is wounded, its configuration changes. Thus, it possess potential On unwinding, the potential energy moves hands of watch, by being converted into               kinetic energy.
  • Similarly, a stretched bow and arrow system, a cocked-up spring of an air gun, a stretched catapult, water stored high up in the dams, a stone lying on the top of the roof etc., posses               potential energy.
  • Magnetic energy, chemical energy, nuclear energy, energy of static elec­tricity are the forms of potential energy.
  • Law of conservation of energy states that the energy can neither be created, nor can be destroyed, It may be transformed from one form to another form, but total energy of the               system remains constant.
  • The phenomenon of transformation of energy from useful form to use­less forms, is known asdissipation of energy.


  • When hands are rubbed, the mechanical energy due to friction changes to heat energy.
  • When two stones are struck, the mechanical energy changes to heat and light energy.
  • When a knife is rubbed, against grinding stone the mechanical energy changes to heat, light and sound energy.
  • When brakes are applied, the mechanical energy changes to heat energy at the point where brakes rub against moving wheel.
  • When an arrow is stretched in a bow, the mechanical energy changes to potential energy. On releasing string, the potential energy changes to kinetic energy of arrow.
  • The water stored in. dams has potential energy. When this water is released, it changes to kinetic energy of flowing water. The kinetic en­ergy of flowing water turns blades of turbine said changes to mechanical            The mechanical energy of turbine drives dynamo and changes to electric energy.
  • When a torch is switched on, the chemical energy changes to electric energy. The electric energy on flowing through filament of bulb changes to heat and light energy.
  • The electric energy in an electromagnet changes to magnetic energy.
  • The electric energy flowing through an electric motor or fan changes to mechanical energy. It partly changes to heat energy.
  • The sound energy in a microphone changes to electric energy.
  • The electric energy changes to sound energy while flowing through speaker.
  • In an electric heater, electric oven, electric geyser etc.; the electric en­ergy changes into heat energy.
  • In steam engine, the heat energy of steam changes to mechanical energy.
  • In an electric generator, the mechanical energy changes to electric energy.
  • In photo voltaic cell, the light energy changes to electric energy.
  • In Television, the electric energy changes to sound and light energy.
  • When fuels are burnt the chemical energy of fuels changes to heat energy.
  • In matches, due to friction, the chemical energy changes to heat and light energy.
  • When a cracker is exploded; the chemical energy changes to heat, light and sound energy.
  • During photosynthesis, the light energy changes to chemical energy.
  • During charging of battery, the electric energy changes to chemical energy.
  • During respiration, the chemical energy of food changes to heat energy. It is the heat energy which keeps our bodies warm. It is the heat energy which changes to mechanical energy when we do perform
  • During nuclear fusion or fission, it is the nuclear energy, which ulti­mately changes to heat and light
  • During the pumping up of water into an overhead tank by an electric motor pump, the electric energy changes to kinetic energy of water. The kinetic energy of water, then changes to potential energy of the            stored water.


  • Pressure is defined as the thrust acting per unit area of the surface of contact i.e., P = F/A

Where ‘P’ is the pressure, ‘F’ is the thrust and ‘A’ is the area over which the thrust is acting.

  • The SI unit of pressure is known as
  • al (V) P = V.I.


  • Fuse is a safety device in an electrical circuit.
  • It is the weakest point In an electrical circuit.which melts and breaks the electric circuit, when the circuit gets :

(i) overloaded due to large withdraw of current,

(ii) due to short-circuiting in the electric circuit,

  • due to fluctuations of current in power supply system.
  • Fuse wire has a low melting point, and high resistance.
  • Earthing protects the user and the appliance from electric shock and bum out respectively.
  • Household distribution of electricity is done in parallel, so that:

(i) if there is short-circuit or overloading in one particular circuit, then only the fuse of that circuit will melt, but the power supply to other circuits is not affected.

(ii) As the resistance due to appliances goes on increasing, the over­all resistance of circuit decreases. Thus, more current flows in the various circuits depending upon the resistance of appliances. Hence, each appliance receives optimum amount of current, while potential difference at the-ends of each, appliance remains the same.

  • Switches are always placed in live wire, so that an appliance is com­pletely cut off from live wire in off Thus, a user will not re­ceive any accidental shock.
  • According to new international convention for colour coding of electric wires, brown is for live wire, light blue for neutral wire and green or yellow for earth wire.
  • Nichrome and Manganin are the common alloys used for making heat­ing elements of electric           appliances, because they have good resistivity, high melting point, low thermal expansion and do not get           oxidised till 1000°C.
  • In most of the cases, nichrome is used as heating element, e.g., in electric iron, electric heater, geyser
  • The heating element of heater becomes red hot, but not the connect­ing wires, because the resistance            of connecting wires is extremely small as compared to the element. So, the heat produced in connecting            coils is much less compared to that produced in element.
  • The filament of electric bulb is made up of tungsten.
  • The bulb is filled with a mixture of nitrogen and argon gases at very low pressure.


  1. During electrolysis, amount of the mass deposited on the electrode is directly proportional to the amount of electricity passes through it.

M  Q           M = ZIT

where, M = amount of mass deposited Q = charge   I = current

T = time

Z = electrochemical equivalent of element (ECE)

  1. During electrolysis, the amount of different elements deposited from the same current is proportional to their electrochemical equivalent.


  • Direct Current or DC is that whose magnitude remains constant as a function of time. An Alternative Current or AC is that which varies in magnitude continuously and whose direction varies periodically.


  • When a current carrying rectangular conductor is placed in a magnetic field at right angles to it, the forces acting on the two parallel lengths will be equal and opposite thus constituting a couple. The conductor            therefore rotate. This is the principle of electric motor. (The EM doesn’t work on the principle of electro-           magnetic induction)


  • It works on the reverse principle of the motor, i.e. Electro-magnetic induction.


  • Transformer is an electric device, by which the e.m.f. of an alternating current can be increased or decreased as per need of a particular situ­ation. The relation between the o/p voltage and i/p voltage is


The current ratio is in the inverse proportion in the case of step-down transformer




  • Force of attraction or repulsion between two point charges is directly proportional to the product of thier magnitude of charges and inversely proportional to the square of the distance between them and                 acting in the direction of the line joining the points. In SI system

F =

SSC CGL Physics Notes


  • The force experienced by a point charge of 1 coulumb in any electric field is called the intensity of the- electric field the point. It is a vector quantity and its unit is

Unit – N/C (N)                                                    F =    N/C



  • It is defined as the amount of work done fYV) in bringing a charge (qo) from infinity to any electric field.

V =  volt



  • The amount of work required in moving a charge of 1 Coulumb from a point to the another is called the potential difference between those points.


  • In case of pure metal the resistance increases with increase in tem­perature and vice-versa. It is given by the relation  =  (1+t) ( = coefficient of thermal resistance)



  • The rate of loss of electric power in any electric circuit is called the power (W)
  • Power = current x voltage
  • W = VA
  • Watt = volt x ampere


  • The amount of electric current passes through any conductor is di­rectly proportional to the potential difference between its both ends i.e. V = IR, (Unit = Ohm)
  • Ice has the highest specific latent heat. So, compared to other matter, it requires higher amount of energy for melting. That’s why;
  • Water bodies in cold countries do not freeze suddenly,
  • Snow melts slowly on the mountains in the summers, due to which, there are no flash floods, and the rivers contain water for whole year,
  • Soft drinks are cooled by ice rather than iced cold water.
  • Boiling point of a liquid rises with presence of dissolved impurities.
  • The phenomenon due to which, a liquid changes into its vapour state at any temperature, without the aid of any external source of heat is called evaporation. Evaporation is basically the internal property of


  • Light is the physical cause which produces sensation of sight and makes the surrounding objects visible to
  • Bodies which themselves emit light are called luminous objects. The luminous objects are usually hot. However, cold luminous objects also exist. The sun and the stars are examples of hot luminous objects,             whereas, the light emitting diodes used in digital instruments are ex­amples of cold luminous objects.
  • Objects which do not emit light themselves are called non-luminous objects. They become visible to us only when the light reflected (or scattered) by them is able to enter our eyes.
  • In a pin-hole camera, the image is always at focus, real, inverted and usually smaller than the object.
  • If the size of the pin-hole is increased, the image becomes blurred.
  • When the object is moved towards the pin-hole camera, the size of the image and its luminosity
  • When the screen is moved towards the pin-hole camera, the size of the image decreases but its luminosity increases.
  • Reflection is the phenomenon whereby light, on striking a surface is thrown back into the same medium.
  • An opaque body absorbs some of the light that falls on it and reflects the remaining light.
  • A transparent body like glass or water transmits almost all the light through it and does not reflect any
  • A smooth shining surface like a mirror reflects away almost all the light that falls on it.
  • When rays shooting from a point object, after reflection or refraction, appear to converse at a second                point, the second point is known as the real image of the first. A real image can be received on a screen                as it is actually formed by the intersection of rays.
  • When rays shooting from a point object, aften reflection or refraction. appear to diverge from a second point, the second point is said to be the virtual image of the first. A virtual image has no existence.             Hence, it cannot be received on the screen.


  • The image formed by a plane mirror is erect; laterally inverted and vir­tual. Also, it has the same size as the object and is as far behind the mirror as the object is in front of it.
  • A polished surface is visible only from that direction in which it re­flects the light.
  • In reflection from irregular surfaces, the object can be seen from all directions.
  • A man can see the whole of his body in a mirror, the size of which is half of his own height.
  • The minimum size of a plane mirror required to be fixed on the wall of a room so that an observer at the centre of the room can see the full image of the wall behind him is one-third the height of the wall behind the observer.
  • A set of two parallel mirrors, therefore, produces theoretically an infi­nite number of Images. However, in practice only a limited number of images are observed, since each successive image is fainter than the proceeding one.
  • The total number of images formed by two plane mirrors inclined at right angles is 3.
  • The portion of the mirror from where reflection actually takes place is known as Aperture.
  • In a concave mirror, the image is always real except when the object is within the focal length. In the latter case, the image is
  • In a convex mirror, irrespective of the position of the object, the image is always behind the mirror. It is always virtual and the image distance from the mirror is always less than the object’s distance.
  • The image formed by a concave mirror might be an enlarged or dimin­ished one depending upon the position of the object. But in a convex mirror, the image is always a diminished one.
  • A concave mirror is used as shaving mirror. Doctor’s reflector, reflec­tors of search light, telescope etc.
  • A convex mirror or a diverging mirror is used as driving mirror and street lamp reflector.













Leave a Reply

Your email address will not be published. Required fields are marked *