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Physics terms A-L.

posted Feb 8, 2015, 10:15 PM by Ranmini Perera   [ updated Jul 3, 2019, 9:46 PM by Upali Salpadoru ]


  • Fig. Light reflecting from inside a cup .

  • ABERRATION -  Distortion of an image due to unequal bending of different coloured light.

    Caustic curve formed in a cup of tea. 

    When the parallel light reflects from the inside of a tea cup you can see this curve.

     This is called   spherical aberration.

  •  A - Symbol for the unit Ampere in electricity.
  •  Ar - Relative atomic mass.
  •  α - Symbol for acceleration.
  •  AC or ac. = Alternating current.  This is the type of current supplied to houses. The flow of current changes 50 times in one second. It is called 50Hz.

  • ABSOLUTE ZERO  -The lowest possible temperature.  -273° C.   or  0. Kelvin According to Kinetic theory all molecular vibrations should cease at this point.  But it has been now shown that molecules could still possess some energy.
  • ABSOLUTE TEMPERATURE - Thermo dynamic temperature . Celsius temperature can be converted to Absolute by adding 273.
  • ACCUMULATOR - A battery that can be charged when discharged such as a lead acid car battery.

Any object, totally or partially immersed in a fluid, gets an upthrust  equal to the weight of the fluid displaced by the object.

  • ATOM

Smallest part of an element which is made up of sub atomic particles.   The lightest atom, Hydrogen is made up of a positively charged particle called a proton and a negative particle called an electron orbiting around it at quite a distance .

Fig. Ernest Rutherford model of the atom.

This is the pressure due to the envelope of air surrounding the Earth.

Fig. Aneroid Barometer.

This has to be measured by using a Barometer. Mercury barometer and the Aneroid barometer are the two common types.
The determination of this is crucial for weather forecasting.
The normal atmospheric pressure at sea level is 103360 Pascals. Sometimes this is given in a unit called a ‘bar’.   1 bar = 105 Pa.
  • AMPERE -  Unit for measuring electric current.
  • AMPERE HOUR - The charge that has passed when a 1 A current has flown for 1 hour.
  • AMPLITUDE- Largest displacement of a particle  in a wave.

  • BAR 
         A unit for the measurement of pressure.  1 Bar = 10 Pascals.
         An instrument to measure atmospheric pressure.There are two main types; Fortin's barometer              which use a mercuy column to balance the atmospheric pressure and the Aneroid barometer                which uses the compression on a metal plate and amplified by a lever mechanism.   
         In common conversation the Leclanche's cells used in flash lights etc, are called batteries but a              battery really means a collection of cells connected in series.
         The car battery is really an accumulator.

Developed in 1805 by Sir Francis Beaufort, U.K. Royal Navy

Scale name

Speed  meters/ second

Effects On Land

On  sea



Smoke rises vertically

Mirror like sea

1.Light air

1 - 2

Smoke shows wind.

Ripples arise

2. Light breeze

2 - 3

Feels on face. Leaves rustle.

Small waves.

3. Gentle breeze

4 - 5

Small twigs sway.

Crests break

4.Moderate breeze

6 - 8

Dust rises. Small branches move.

Longer waves with white caps.

5 Fresh breeze

9 - 11

Small trees move.

Waves over 4m long. Spray appears.

6 Strong breeze

12 - 14

Wires whistle.

Waves over 12 m. Lot of spray.

7. Near gale

14 - 17

Trees move.  Resistance felt when walking.

Waves up to 19 m. Lot of foam.

8. Gale

17 - 21

Twigs break up.

Foam brown in streaks.

9. Strong gale.

21 - 24

Loose sheets fly off the roof tops.

Spray covers vision.

10. Storm

25 - 28

Trees topple or break.

Waves over 30 ft.

11. Violent storm

29 - 32

Waves over 40 ft.

12, Hurricane


Visibility extremely poor. Air filled with foam.

 This principle states that an increase in the speed of a fluid causes a reduction in pressure. This is made use of in many sprayers.
Low pressure caused by the movement of air causes the liquid to rise.

These are the negatively charged rays coming out of radioactive substances. They really consist of fast moving electrons.
  •  Bose-Einstein condensates  .

Satyendra Nath Bose.Indian (1894-1974) predicted the existence of a 5th state. Eric Cornell and Carl Weiman cooled a sample of rubidium to within a few degrees of absolute zero. Then the molecular vibrations ceased and division into atoms disappeared and formed into a super atom. This condition exhibits the properties of super fluids.

Fig. A diagram of a capacitor.

A device that can store an electric charge in electrical circuits.
When the terminals of  high voltage DC is connected to the two plates , they develop opposite charges and exhibit an electric field between the plates.

    This is the ability of a capacitor to acquire a charge.  Unit of capacitance is Farad.  If a capacitor can hold one coulomb of charge when a voltage of 1V.  is applied the capacity would be 1 Farad. (F)
Capacitance depend on the area and nature of the plates, the gap between the plates and the material (dielectric) in between.
When thin tubes are dipped in water as shown here, the water level rises.

There are 3 forces that determine the capillary action.

1.      Cohesive force- In water every molecule gets pulled by the surrounding water molecules. ( Except the top layer, that will have no water molecules above them. This is the cause of surface tension)This is the inter molecular force between the molecules of the same kind in a liquid.

2.      Adhesive forces- This is the attractive forces between unlike molecules. When water is in a vessel, the molecules of the vessel, glass or metal will attract the water molecules. This is the reason for the curved meniscus in water and mercury as shown here

Movement of an object around a fixed centre. It may be uniform or varying. Even if the speed of the object is the same the velocity will not be the same as the direction is changing. As the velocity is changing, there has to be an un balanced force acting.  This will be towards the centre and is called the Centripetal force.
Convection currents occur in liquids and gases. In the case of a fire hot gases expand and rise due to decrease in density. This is the reason why the flames try to go upwards. Cooler air from the surrounding comes to fill the gap.
A substance that can easily transfer an electric current is described as a good conductor.
Similarly a substance that can transmit heat becomes a good conductor of heat.
Usually metals or good conductors of heat and electricity. 
(Opposite = Insulator)

         Calculations show that up to 90% of the universe should contain a mysterious substance which              has been detected only by its gravitational effects.
  • DC - Direct current. Electric current flowing only in one direction; positive to negative,
Mass of a unit volume. Usually given as grams per cubic centimetre or  per litre. The maximum density of water is 1g/cm3
        Formula:-              Density =  Mass / Volume.       
                                 That is:  D =M/V
Temperature at which air becomes saturated with water vapour present.
The spreading of a wave when it reaches an edge or an aperture.

Random motion of molecules specially in a gas. The smell of a flower spreads due to the diffusion of molecules from the flower.

Angle of deviation This is the change of direction due to refraction as shown below.




A device that allows the current to flow only in one direction; really an electric valve. If the current is reversed in this circuit the bulb will not light.

LED is a light emitting diode.


the separation of white light into colours or of any radiation according to wavelength.

This is a length measure considering the direction. It is a vector quantity. Go to velocity.
          A beam of rays may be parallel, diverging (spreading) or meet at a point (Converging) 

Please click Wave propertiws.


Dry cell.jpg

Allmost all kinds of dry cells are adaptations of the Leclanche's cell.  He used Carbon (graphite) and zinc as electrodes and a solution of ammonium chloride as the electrolyte.
As dry cells cannot have a liquid they use a paste keep the electrolyte moist.

This a ration to compare useful work obtained as to the total work done.
Efficiency =  Useful work / Total work
This can  also be  used to compare energy.
This ratio multiplied by 100 gives the Efficiency percentage.
  • Electric charges.
        In matter, normally the protons and electrons are balanced. So they are electrically neutral.

Electric current

This is the flow of electrons in a conductor. The electrons move from the negative terminal to the positive terminal but it is the convention to say that the current flows from positive to negative.

The current is measured in Amperes while the electrical pressure is given in Volts.

ii.    Direct current DC-This is the current we get from a cell or a battery. Current flows in one direction.

iii.    Alternating current AC-The current supplied to houses is of this nature. It reverses the direction of flow 50 times per second.  This is described as 50 Hertz.

iv.    Common Symbols used in Electrical Circuits.

Formulae connected with electricity

Ohm’s Law

The current flowing through a conductor is directly proportional to the potential difference (Voltage) applied across the two ends, provided the conditions such as temperature remains the same.

1.    This equation is derived from Ohm’s law.

      Resistance =  Potential difference / Current
     That is     R =  V /I       ( V= Volts, and I = Current in Amperes R-resistance in Ohms.)

2.    The product of current and time gives you the quantity of electricity in Coulombs. 
      Quantity = Current x time
     That is       Q = Amperes x seconds.
                   Q = I t.
3.    Electrical energy is measured in Joules.
       Joules = Volts x Current x time
                  J= VIt 
4.    Power is the rate of using energy. The unit for this is the Watt.
       Watt = VIt /t
       As t cancels the formula is     W = VI

5.    Resistors in Series and parallel circuits
      Combine resistance of a series circuit
      R  = r1 + r2  (when  r1 and r2 are two resistors connected in series)
6.    For a parallel connection the formula becomes
      !/R  =  1/r1 + 1/r2
7.    Electricity supplied to houses is measured by a unit called Kilowatthour (kWh)
       This is the electricity consumed by 1000W in one hour.  (W=Watt is the unit of power.)

Fig. Circuit for an electric bell.

For an account of this click
Electro magnetism.

         The wod  C R EA M  are the first letters of types of enerhy.

1.Chemical Energy

This is energy absorbed or given out during a chemical change.

Examples :-  1.Burning releases stored up chemical energy as heat and light. Electrical energy passed to a car battery stores it as chemical energy.

2.Radiant Energy

Rays and waves that can radiate in space.

Examples:-   1. Electromagnetic waves ( light, TV waves, X rays etc.)

                    2. Energetic particles from Radioactivity  as from radium

3.Electrical energy

Electric current is a rapid flow of electrons.

Objects can get electrically charged. ( such as the clouds which release the energy in the form of lightening)

4.Atomic energy

Energy stored up in the nucleus of an atom.

Examples :-

1. In the case of the atomic bomb, energy obtained by the breaking up of the nucleus of Uranium.

         2. In the sun energy is released by the fusion of Hydrogen nuclei to form Helium nuclei.

5.Mechanical energy =

This group includes, kinetic energy, potential energy and vibrational energy.


Common properties of these .

a. They travel at the highest velocity attainable. 300.000 km /second. (3 x10ms-1)

b. They can travel in a vacuum.  


 Fig. Electro Magnetic Waves.


Wave length




Gamma rays

Cosmic origin

Radio activity



10-15 to  10 -13

10–13 to 10 -12


10 23  to  10 20

 10 30 to 10 19

Comes from deep space.

 From the nuclei of radio active Isotopes.

Used by particle physicists.

 Cancer treatment.

X ‘ rays

10 -12 to 10 - 9

10 10 to 1017

Bombardment of heavy metal nuclei by fast electrons.


Metal industry.

Ultra violet rays

10 -9 to 10 -7

10 17 to 10 15

Movement of electrons from shells.

Killing bacteria

Fluorescent lighting.

Visible light

10 -6


390 to 750 nm

Vibration of electrons.

Sight of animal



Infra red

10 -6 to 10 -4

1015 to 10 13

Vibration of molecules.




Micro waves

10 -4 to 10 -1

10 13 to 10 9

Rotation of molecular arrangement




TV waves

Radio waves

10 -1 to 10 1

10 1 to 10 4


10 9 to 10 7

Motion of electrons & nuclei in electric and magnetic fields.


  •  ENTHALPY- is the amount of heat content used or released in a system at constant pressure. This isually expressed as the change in enthalpy. 
The change in enthalpy is related to a change in internal energy          
(U) and a change in the volume (V which is multiplied by the constant pressure of the system.
h = Plank's constant.
  •      F
  •  FORCE  A force may be defined as the effect that can change the velocity of a certain mass
               Types of Force

Muscular forces:-   Push, pull, kick etc.

Attractions:-          Electrical, Magnetic, Gravitational.

Repulsions:-          Electrical and Magnetic

Elastic forces:        Reaction forces,(Support force)  Friction.  



Boyle’s Law

Robert Boyle introduced this in 1662.

In a closed system at constant temperature the volume of a fixed mass of gas is inversely proportional to the pressure.

This results in the equation

Pressure 1 X Volume 1 =  Pressure 2 x Volume 2    

                         P1V1 = P2 V2

Charles’ Law

The volume of a fixed mass of a gas is directly proportional to the Absolute temperature at constant pressure.

  • g =  Symbol for gram.

g =  Acceleration due to Force of gravity.  equal to 9.8 ms-2.

Avogadro’s Law - Equal volumes of different gases at the same temperature and pressure  have an equal number of molecules.    V∝n

GALVANIC CELL-  Luigi Galvani (Italy) was an 18th Century biologist . While he was dissecting a frog his scalpel touched a piece of brass. The leg twitched. Further experiments showed that the procedure generated an electric current.  He called it animal electricity.

This was the first instance of getting electricity from a chemical change.

Today even a tiny current developed between some impurity such as carbon in iron when connected by a drop of rain water generates c current it is called   a Galvanic cell.

GAMMA RAYS - Refer electromagnetic Waves. The wave length  10 –13 to  10-12  m.


This is a simple device to detect radio activity.When the rays enter through the mica window gas molecules get ionized. These ions will conduct electricity and current can be detected by the meter.

-GM tube.jpg


A Mnemonic to remember the Eras

Camels often sit down carefully

Cambrian  Ordovician  Silurian  Devonian    Carboniferous

          Perhaps their joints creak.

              Premium  Triassic  Jurassic  cretaceous

                     Possibly early oiling might.

                           Palaeocene  Eocene  Oligocene  Miocene

                                          Prevent premature harm.

                                                                     Pleistocene  Pliocene  Holocene


  •  H - Symbol for enthalpy. 
  •   h  = Symbol for Plank's constant.

  • HEAT 

What is heat ?We can use heat to get work done; and as such it is a form of energy. Electricity is the movement of electrons. Kinetic energy is due to the movement of matter. What is the nature of Heat?

Heat is also a kind of Kinetic energy. It is the Kinetic energy present in the molecules. In a gas the molecules are in rapid motion. So they have translational k.e. In a liquid state also they show some movement. Even in a solid block molecules are not quiet but they vibrate.

The temperature depends on the state of movement. If the vibrations have a high amplitude or a high speed then the temperature will be high. Kelvin temperature has taken this factor seriously.

Heat Transfer

Heat always flow from a hot body (higher temperature) to a cooler body. There are three methods by which this can occur.

1.      Conduction:  In solids molecules are packed close to each other. Vibration of a molecule can disturb the neighboring molecules.  Passing of kinetic energy in this manner is ‘conduction’ While metals are good conductors of heat non metals and liquids (except mercury) are poor conductors. Gases do not conduct at all and referred to as heat insulators.

2.      Convection:-  In a candle flame, the wax vapour combines with oxygen releasing heat. (Chemical energy transferred to heat) As the temperature is very high part of the energy escape as light. Some energy emanate as infrared radiation. (Heat waves)  The hot gases formed. Carbon dioxide and steam carry most of the energy, 

  as internal energy. Due to expansion these gases become low dense which enables them to rise vertically. This creates an upward draft that draws air from the surroundings.             

In Convection molecules move in a stream. This can occur only in fluids. ( In solids molecules are not free to move)

3.      Radiation:-  T

his is the escaping of heat as infrared radiation. The Earth gets energy from the sun by radiation. At high temperatures other rays of the electromagnetic spectrum such as light of different colours are also produced. 


Fig.  Fig. The black and white arrows show convection currents . The red arrows show radiation.


  • HEAT ENERGYJoule is the unit for measurement of energy. One kilogram of water, in increasing the temperature by 1° C has to absorb 4200 Joules.
  • HEAT CAPACITY = The amount of heat required to change the temperature of a body by one degree.Unit J/C°.
  • HERTZ - Unit for Frequency usually given as number of cycles per second.

  •  This is an instrument to determine the Relative Density of a liquid. A special one called a Lactometer is used to test milk.


This is the product of average force and the time it had been acting.
Impulse = F xt..   Impulse is equal to change in momentum.

 This can be a slope that can facilitate to move heavy equipment to a higher level.

The forces due to an object on an incline. What do you think is the force necessary to stop the ball moving?

This is the reluctance of a mass to change its state of motion.
In the case of rotatory motion it depends on the torque.  Inertia = Torque / angular acceleration.
  •  ION
An ion is an electrically charged particle; a molecule or a radical. Examples H+  and OH -
When an atom or a molecule loses or gains an extra electron  what results is an negative or a positive ion This process is called ionization.

  • Ionization

  •  JET PROPULSION - All rockets , some planes and some animals in the sea use this mode of getting thrust . This is explained by Newton's third Law.
  • JET STREAM - A very fast moving mass of airin the upper sky  between 
  • K - Symbol for Kelvin ( Absolute temperature)

These are two laws regarding electrical circuits.
First Law:- In a closed circuit the sum of the currents coming in is equal to the sum of the currents leaving.
Second law:-  In a closed loop If you add up the voltages considering the direction of current the result will be zero.
  • In 1827 Robert Brown observed through a microscope the haphazard movement of pollen grain on the surface of water. This came to be known as ‘Brownian motion’ which had to be explained 78 years later by Albert Einstein. He concluded that in a fluid the atoms or molecules are in constant motion and they bang on a particle like a pollen grain. As the resultant force on the particle due to these bombardments changes direction the solid particle shows the zig zag movement.
This movement can also be seen in dust particles in a beam of light.
In the case of solids as the particles are held together by stronger bonds they can only vibrate.
The theory can also explain the phenomenon of pressure in fluids as well as the temperature rise due to gaining of heat energy.
    The Theory  states that matter is composed of a large number of small particles— atoms or molecules—that are in constant vibration or movement. This theory is also called the Kinetic Molecular Theory of Matter .
  • LATENT HEAT-The heat transferred from or to a substance when undergoing a change of state without changing the temperature. On evaporation it is Latent heat of evaporation, on melting it is the Latent heat of fusion.
  • Latent heat of fusion is 336 000 J/kg
  • Latent heat of evaporation is 2250 000 I/kg.

  • LASER- Light Amplification by Stimulated Emission of Radiation.
  • LIGHT-  Electro magnetic waves that may be detected by the human eyes.
  • LIGHT YEAR - The distance light can travel in 1 year.
  • LENSES-  Circular discs usually made of glass, that have concave or convex surfaces to refract light. Used in many optical instruments. Images formed by them.