Notes Notes and pdf Physics physics

Important Scientific Instruments and their usage

Important Scientific Instruments and their usage


It is used to store electrical energy


It measures altitudes and is used in aircraft.


It measures the strength of electric current (in amperes).


It measures the force and velocity of the wind.


It measures the intensity of sound.


It is used for improving the imperfect sense of hearing.


It is used for continuous recording of atmospheric pressure.


It measures atmospheric pressure.


It is used to view distant objects


It measures heat radiation


It measures the quantity of heat.


It is used in an internal combustion engine for charging the air with petrol vapor.


It traces movements of the heart, recorded on a cardiograph.


It determines the longitude of a place in a ship.


It is an instrument used in cinema making to throw on screen and enlarged image of the photograph.


An instrument for comparing intensities of colour.


An instrument to change or remove the direction of an electric current, in dynamo used to convert alternating current into direct current.

Cresco graph

It measures the growth in plants.


A charged particle accelerator which can accelerate charged particles to high energies.


It converts mechanical energy into electrical energy


It measures force, torque, and power


It detects the presence of an electric charge.


It examines the internal parts of the body.


A glass tube for measuring volume changes in chemical reactions between gases.


It measures the depth of the ocean.


It measures the electric current of low magnitude.


It measures the specific gravity of liquids.


It measures sound under water.


It measures humidity in the air.


It graphically records physiological movements (Blood pressure and heartbeat).


It determines the purity of milk.


It measures the pressure of gases.

Mariner’s compass

It is an instrument used by the sailors to determine the direction.


It converts the sound waves into electrical vibrations and to magnify the sound.


It is used to obtain a magnified view of small objects.


An instrument by which the distance covered by wheeled vehicles is measured.


It is used to view objects above sea level (used in submarines)


An instrument for producing sound.


The instrument compares the luminous intensity of the source of light


It is used for comparing the electromotive force of cells.


It measures very high temperature.

Quartz Clock

A highly accurate clock used in astronomical observations and other precision work


Radio, angle, detection and range is used to detect the direction and range of an approaching aeroplane by means of radio micro waves


It measures the emission of radiant energy.

Rain Gauge

An apparatus for recording rainfall at a particular place.


An instrument used for the conversion of AC into DC.


It measures refractive index.


It measures the amount of sugar in the solution.


It determines salinity of solution.


It measures the intensity of earthquake shocks.


This is used by navigators to find the latitude of a place by measuring the elevation above the horizon of the sun or another star.


It is an instrument for measuring the energy distribution of a particular type of radiation.


An instrument used for spectrum analysis


It is an instrument placed in a vehicle to record its speed.


It measures the curvatures of surfaces.


It measures blood pressure.


It is used to view two dimensional pictures.


An instrument which is used by the doctors to hear and analyse heart and lung sounds.


It is used to view rapidly moving objects.


An instrument used in measuring speeds of aero planes and motor boats.


This instrument receives and sends typed messages from one place to another.


It views distant objects in space.


It measures horizontal and vertical angles.


This instrument is used for the measurement of temperatures.


It regulates the temperature at a particular point.


A small device which may be used to amplify currents and perform other functions usually performed by a thermionic valve


It is used to measure the amount of liquid precipitation over a set period of time. It is also called Rain Gauge.


An adjustable scale for measuring small subdivisions of scale


It measures the viscosity of liquids.


It measures the electric potential difference between two points.


Notes on Atomic models and Quantum numbers

➤Atomic Models:

To show the arrangement of fundamental particles in an atom various models were proposed, some important models are as follows:

➤Dalton’s Atomic Theory:

The different assumptions of this theory are as follows;

• All matters are made up of atoms which are indivisible and indestructible.

• All the atoms of a given element have identical properties including identical mass.

• Atoms combine in small whole numbers to form the compound.

• Chemical reactions involve only combination, separation or rearrangement of atoms.

➤Thomson’s Atomic Model:

• Every atom consists of uniformly positively charge sphere having the radius in the order of 10-10 m  in which entire mass is uniformly distributed and negatively charges electrons are embedded randomly.

• Thomson uses the cathode ray tube to gives its atomic model.

• This model is known as the plum pudding model.

• According to him, negative charge particles are distributed in the atom and to balance this negative charge some positive charge particles also present in it.

• The atom as a whole is neutral.

➤Drawbacks of Thomson’s Atomic Model:

• It could not explain the origin of spectral series of hydrogen and other atoms.

• It could not explain large-angle scattering of alpha particles.

➤Rutherford’s Atomic Model:

• He fired a beam of the alpha particle on a sheet of gold to gives its model theory.

• The existence of nucleus was proved by Rutherford in his alpha particle scattering experiment.

• The entire positive charge and almost entire mass of the atom is concentrated at its centre in a very tiny region of the order of 10-15m, called the nucleus.

• The negatively charged electrons revolve around the nucleus in different orbits.

• The total positive charge on the nucleus is equal to the total negative charge on electron; therefore atom as overall is neutral.

• A nucleus consists of positively charged protons and electrically neutral neutrons.

➤Limitations of Rutherford’s Atomic models:

• According to Maxwell electromagnetic wave theory, an accelerated charged particle emits its energy in the form of electromagnetic waves. Therefore an electron must emit emits energy during its course of accelerated motion around the nucleus. Due to which the radius of its path will decrease gradually and ultimately it will fall in the nucleus.

➤Plank’s Quantum Theory:

 Planck gave a new revolutionary theory of radiation known as the quantum theory of radiation.

According to this theory

Radiant energy is not emitted or absorbed continuously but discontinuously in the form of small packets of energy known as photons (quanta).

The amount of energy associated with a quantum of radiation is proportional to the frequency of radiation.

Energy = hν

Where h is Planck’s constant

➤Bohr’s Model:

• Bohr’s model is based on the quantum physics i.e. quantization of energy

• This model is similar to the planetary model in which electron revolves around the nucleus in the specific orbit

• Bohr’s model is considered as the primitive hydrogen atom model

• Every orbit has a specific size and energy level.

• Smallest energy is found in the smallest orbit as energy is related to the size of the orbit.

• Electrons can move from one orbit to another by emitting or absorbing energies according to quantum mechanisms.

➤Heisenberg’s Uncertainty Principle:

• According to this theory, the position and velocity or momentum cannot be measured at a single instant.

• Heisenberg principle is not applicable to macroscopic objects

➤De-Broglie Concept:

• De Broglie states that electron has dual nature i.e. wave nature and particle nature

• Wavelength (l) of an electron is inversely proportional to its momentum (p)

        l=h/p=h/mv, where h is Planck’s constant


The electron has a definite energy characteristic of the orbit in which it is moving. These orbit or energy levels or shells therefore also known as stationary orbits.


Shell =K,L,M,N

The shell with n=1 is closest to the nucleus and an electron in this level has the lowest energy as it is closest to the positive charge of the nucleus.

➤Distribution of electrons in different orbits:

• It was suggested by Bohr and Burry and the rules that govern it are as follows:

• The maximum number of electrons present in a shell is given by the formula 2n2 where n=1,2,3 and 4 for K, L, M and N shells respectively.

• The maximum number of electrons that can be accommodated in the outermost orbit is 8.

• The shells are filled in a step-wise manner.

➤Electronic Configuration:

• It is the arrangement of electrons in various shells, subshells and orbitals in an atom.

• It is written as 2,8,8,18,32  

• The maximum number of the electron in a shell is given by 2n2

➤Filling or orbitals in Atoms:

The filling of electrons into orbitals of different atoms takes place according to the Aufbau Principle, Pauli Exclusion Principle and Hund’s rule of maximum multiplicity.

According to Aufbau principle in the ground state of an atom, electron enters the orbital of lowest energy first and subsequent electrons enter in the order of increasing energies.

The lower the value of (n+l) for an orbital, the lower is its energy.

here l is the azimuthal quantum number and n indicates the principle quantum number

If two orbitals have same (n+l) value, the orbital with the lower value of n has lower energy.

Hund’s rule of maximum multiplicity deals with the filling of electrons into the orbitals belonging to the same sub-shell. According to this rule, electron pairing will not take place in the orbital of the same energy until each orbital is first singly filled with parallel spin.

➤Quantum Numbers:

Each electron in an atom is characterised by a set of definite values of three quantum numbers n, l and m. In addition of these three numbers, fourth quantum numbers is also needed which specifies the spin of the electron.

1. Principal quantum number (n):

Determines the main energy level of the shell in which the electron is present.

The various values of n are 1, 2, 3 and 4 etc. also known as K, L, M and N etc. respectively, as the value of n increases the energy of electron also increases.

2. Azimuthal quantum number (l) determines the sub-level or sub-shell (s, p, d and f) in a given principal energy level or shell to which an electron belongs.

3. Magnetic quantum number (m) gives information about the orientation of the orbitals.

Spin quantum number(s) describe the spin orientation of the electron; the electron can spin only in two ways, i.e. clockwise or anticlockwise.

4. Pauli Exclusion Principle:

It states that no two electrons in an atom can have the same set of four quantum numbers.