Gauss's law : The net electric flux enclosed by a surface is To times,

Definitions and laws

the charge enclosed by the surface.
↑

Electric charge : It is the intrinsic property.S.I unit is Coulomb (C). Electrostatic potential energy difference : It is the work done by an
Coulomb's law: The force of attraction or repulsion between two charges is external force in moving a charge Q from one point to another.
directly proportional to product of the charges, and it is inversely Electrostatic potential energy : potential energy of charge Q at a point
proportional to the square of distance between them. is the work done by the external force in bringing the charge Q from
infinity to that point.
E =

Tis 9
I Ea
U =
Unit :
joule(i)
Electric flux : Number of electric field lines passing normally through
a surface is known as electric flux. Electrostatic potential : It is the amount of work done by an external
Unit Nm2C force in bringing a unit positive charge from infinity to that point.
. :

q E =

Electric field : electric field at a point P is defined as the force

V
=E Unit : Volt (v)

experienced by a unit positive charge placed at that point. Capacitance : It is the ratio of charge stored in the capacitor plates to the
potential difference across the capacitor plates.
= unit : NC-

= fard
c Unit : e

Electric dipole : Two equal and opposite charges separated by a very small
Capacitor : It is a device used to store charges and electrostatic energy. It
distance is known as electric dipole.
has two parallel plates separated by a distance ,d.
Electric dipole moment : It is a vector whose magnitude is a product of Electrostatic shielding: the net electric field inside the cavity is always
either of the charges and distance between them. zero.
Unit Cm :

p (2019) P
=

Equipotential surface :equipotential surface is a surface with a constant

Quantisation of charge : The total charge of the system is equal to an value of potential at all points on the surface.
integral multiple of basic charge, e. Polar molecule : polar molecule is one in which the centres of positive
ne
q =

and negative charges are separated. Such molecules have permanent

Superposition of force: In a system of N particles the net force acting dipole moment.
on one charge is equal to the vector sum of the forces exerted on the Example, water and HCl
charge by all the other charges. Non - polar molecule : in non-polar molecules, the centres of positive
and negative charges coincide. The molecule has no permanent dipole
Exot = I +..... I moment.
Linear charg density : charge per unit length. [x =
4] unit : Cm
+
Example, oxygen and hydrogen
unit : (m Polarisation: when a polar or a non-polar molecule is placed in an
Surface charge density : charge per unit area. [u = external electric field, it develops a net dipole moment. The net dipole
Unit : Cm moment per unit volume is called as polarisation.
Volume charge density : Charge per unit volume. [f =

] i =E
.
 Definitions and laws

Electric current : The rate of flow of charge is known as electric Temperature coefficient of resistivity: it is defined as the ratio of increase in resistivity
current. per degree rise in temperature to its resistivity at standard reference temperature.

Ohm's law: The current in a conductor is directly proportional to

Power: It is the rate at which the electrical potential energy is delivered.
the potential difference across the ends of the conductor.

Resistance :The opposition shown by the resistor to the flow of emf :It is the voltage provided by the battery when no current flows in the external
current is known as resistance. circuit.

Terminal voltage: it is the potential difference across the terminals of a load when
Resistivity: It is defined as the resistance of a conductor of unit, current flows in a circuit.
cross-section area and unit length.
Internal resistance:The battery is made up of electrodes and electrolyte. There is
resistance to the flow of charges within the battery and this resistance is called as
Conductivity: It is defined as the reciprocal of resistivity. internal resistance.

Current density : Electric current per unit area.

Kirchhoff's rule:
First rule :The net electric current at a junction is equal to zero
Drift velocity: The average velocity attained by electrons between
two successive collisions when subjected to an external electric
field is known as drift velocity. Second rule : The sum of all voltages around a close loop in a circuit must be equal
to zero.

Relaxation time: The time taken between two successive Mobility: The drift velocity attained per unit electric field.
collisions.
 Definitions and laws

Biot - savant Law :It states that the magnitude of magnetic field is Ampere’s Circuital law : the line integral of. is equal to times
proportional to the current, element length, and is inversely proportional to current enclosed.
the square of the distance .

Faraday's Law: Change in flux produces emf.

Change in flux is directly proportional to the induced emf.
Flemings left hand rule :The thumb, the fore finger and the middle finger
of the left hand are projected in mutually perpendicular directions. If the
fore finger represents the direction of magnetic field and the middle finger
Lenz's law:The polarity of induced emf is such that it tends to produce a
represents the direction of the charge or the current, then the thumb gives us
current which opposes the change in magnetic flux that of produces it.
the direction of the force experienced.
Fleming’s right hand rule : The thumb, the fore finger and the middle
finger of the right hand are opened mutually perpendicular to each other.
Then the thumb points towards the direction of motion of the conductor Self inductance:It is defined as the flux linkage with the coil when
related to the magnetic field,The fore finger points towards the direction of one ampere current flows through it.
the magnetic field and the middle finger points towards the direction of
induced current.
Right hand thumb rule :Curl the palm of your right hand around the Mutual induction:When an electric current passing through a coil
circular wire with the fingers, pointing in the direction of the current, the changes with time, an emf is induced in the neighbouring coil. This
right hand thumb gives the direction of magnetic field. phenomenon is known as mutual induction.
Mutual inductance: Mutual inductance is defined as the flux
Right hand rule :When you hold the wire in your right hand, with your linkage with the second coil, when one ampere current flows through
thumb pointing in the direction of the current then your fingers will curl the first coil.
around in the direction of the magnetic field.

Torsional constant : It is the restoring torque per unit twist . Gauss's law in magnetism: The magnetic flux through any closed
surface is equal to zero.
Current sensitivity:It is defined as the deflection per unit current.

Voltage sensitivity: it is deflection per unit voltage . Self-induction: If the flux is changed by changing the current in the
coil and emf is induced in the same coil. This phenomenon is known
as self induction.
 &

Definitions and laws :

Inductive reactance: It is the opposition offered by the inductor to
the flow of current through it.
Magnetic susceptibility : It is defined as the ratio of the Intensity of
Unit Ohm (ef
magnetisation (M) to the the magnetising field (H). X = Lw :

Capacitive reactance:It is the opposition offered by the capacitor to the

Xm =

Ite No unit
flow of current through it.
Xc
= 1
CW
Unit : ohm (et

Relative permeability: It is defined as the ratio between absolute permeability of Impedance : The net opposition offered by a series LCR circuit to the
the medium to the permeability free of space. flow of current through it.
Unit :
Ohm(e)

to
V
Mo (X Xc)2
z =
= ,
-

Electrical resonance: When a system is driven by an energy

source at a frequency, that is near the natural frequency, the
Magnetic induction: The magnetic induction is equal to the sum of magnetic amplitude of oscillation is found to be large and the current in the
field produced in vacuum due to the magnetising field and the magnetic field circuit will be maximum.
due to the induced magnetism of the substance. Q-factor:The degree of sharpness of resonance is known as Q -
unit : Tesla (T)
- =
Mo (F +TY)
factor.
a
V
=

Displacement current:The changing electric field produces

Intensity of magnetisation: the net magnetic moment per unit volume of the
displacement current.
material. in
Ed
unit Amt : =

T =

Lume
Modified Ampere's - Maxwell Law:
d [ic "d ]
65 .
=
Mo +

Magnetising field or Magnetic intensity:The magnetic field which is

used to Magnetize a sample is called magnetising field.(Fi)
=
Moic +
MoEo (d)
Unit : Am

Maxwell's Law:Changing electric field produces a magnetic field.

Electromagnetic induction:The process in which change in magnetic
· B dT - (P)
.
= =

- &E .
flux induces an emf is known as electromagnetic induction.
 Definitions and laws :

Laws of refraction: Stopping potential: It is that value of the negative (retarding) potential given
(1)The incident ray, the refracted ray and the normal are co-planar. to the collecting electrode A which is just sufficient to stop the most energetic
(2)The ratio of sine of angle of incidence to sine of angle of photoelectrons emitted and make the photocurrent zero.
refraction is equal to constant
De-broglie hypothesis: All metal particles in motion are associated with
waves(material particles can behave as a wave). These waves are called debris,
waves or matter waves.
Laws of reflection:
(I) The incident ray, the reflected ray and the normal are co-planar. Distance of closest approach: the minimum distance between the centre of the
(2) angle of incidence = angle of reflection. nucleus and the alpha particle just before it gets reflected back by 180°.
Total internal reflection:When the angle of incidence is greater than
the critical angle, the incident ray is reflected back to the medium.
This phenomenon is known as total internal reflection. Impact parameter:The perpendicular distance between the centre of the
nucleus and the direction of initial velocity vector of the alpha particle.

Interference: The phenomenon of superposition of two light waves which

produces increase in intensity at some points and decrease in
intensity at some other points is called interference of light. Excitation energy:The energy required to excite an electron from lower
energy state to any higher energy state is known as excitation energy.
Diffraction: It is bending of waves around sharp edges into the
geometrically shadowed region . Ionization energy : The minimum energy required to remove an electron
Polarisation:The phenomenon of restricting the vibrations of light to from an atom in the ground State is known as ionisation energy.
one direction perpendicular to the direction of propagation of wave is
called polarisation of light.
Photoelectric effect:When an electromagnetic radiation of suitable Excitation potential: excitation potential is defined as excitation energy per
frequency is incident on the surface of the metal, electrons are unit charge .
ejected from the metal surface. this phenomenon is known as
Ionization potential : It is defined as the ionisation energy per unit charge.
photoelectric effect.
Work function: The minimum energy needed for an electron to escape Mass defect:The difference in expected mass and actual mass of a nucleus is
from the metal surface is called work function of that metal. known as mass defect.

Threshold frequency: The minimum frequency required for the

photoelectric effect to take place.
Binding energy:It is the energy required to bind all the nucleons
together, or it is the energy required to break the nucleus into its
constituents.

Fusion: lighter nuclei fuse into stable, heavier nuclei.

Valence band:The occupied energy states form a band known as

valence band.

Fission: heavy nucleus split into stable, lighter nuclei.

Isobars:Nuclei with different atomic number and same mass number.

Isotopes:Nuclei with same atomic number and different mass number.

Isotones : nuclei with same number of neutrons is known as isotones.

Conduction band:The unoccupied energy states from a band known

as conduction band.

Energy band gap :The gap between the top of the valance band and the
bottom of the conduction band is called as the energy gap.

Intrinsic semiconductor:Purest form of semiconductor.

Extrinsic semiconductor:When a small amount of dopant is added to

the pure semiconductor, the conductivity of the semiconductor is
increased. Such materials are known as extrinsic semiconductors.