Descriptive questions:

Basic properties of charges:

· Additive ·
Quantisation ·
Conservation

Total & =
Algebraic Q = ne Charges can neither be

sum
of all charges created nor destroyed

Properties of electric field lines:

· For positive isolated charge field ,
lines are in radially outward direction
.

isolated
· For
negative charge field , lines are in radially inward direction.

Electric field lines start

from positive charge and end at negative charge
·
.

· Electric field lines are continuous

.

·
Electric field lines do not form closed
loops.
the direction that
The tangent drawn at
point gives of field at
point
·
a .

·
Two electric field lines never intersect each other .

Properties of equipotential surface:

Work done to
charge from point to another equipotential
·
move a one on an

is equal to
surface zero
.

·
Electric field is normal to equipotential surface
.

Temperature depends on resistivity:

is
Conductors
Temperature coefficient of resistivity positive for conductors
·
: .

f =
ne2

When temperature is increased , no .

of collissions increase then ,

relaxation time I ,
decreases and hence resistivity increases
.

is
Semiconductor : Temperature coefficient of resistivity negative for semiconductors
·
.

When temperature is increased , no .

of free electrons increase and

resistivity decreases .

Ohm's law limitation:

·

voltage ceases to be
proportional to current .

·
In GaAs ,
there is more than one value of V for same I

for the in forward bias the current

In diodes , value
of voltage reverse and
·
same ,

is different.
 Motion in a magnetic field:

Properties of magnetic field lines:

Behaviour of dielectric and conductor when placed in uniform external electric field:

Analogy : inertia and self inductance :

Lenz's law and conservation of energy:

Electrical resonance:

Properties of electromagnetic waves:

Total internal reflection:

Electromagnetic spectrum:

Radio waves: cellular phone-tele communication.

Microwaves: radar system used in aircraft navigation, microwave ovens.

Infrared waves: infrared lamps, Helps in green-house effect, electronic devices such as
TV sets, video recorders and hi-fi systems night vision goggles

Visible rays: vision, fibre optic communication.

UV rays: LASIK, to kill germs in water purifier

X-rays: Treatment of cancer, to diagnose defect in bones

Gamma rays: Destroy cancer cells.

 Transformers : Principle: electromagnetic induction and mutual induction.

Construction: It has two coils - primary and secondary coil, which have high mutual inductance.it is wounded on a
laminated iron core.

Working: The input voltage is connected to the primary coil. AC Current flows through the primary coil. The magnetic
fund linked with the coil changes and emf is induced in the secondary coil.

Energy losses in transformer and methods to reduce it :

Huygen's principle:

Wavefront:
Advantages of reflecting telescope over refracting telescope:

Reflecting telescope has no chromatic and spherical aberration.

Reflecting telescope require less mechanical support.
Reflecting telescope is cost efficient.

Types of electron emission:

Thermionic emission: emission of electrons due to temperature raise.
Field emission: emission of electrons due to applied external electric field.
Secondary emission: emission of electrons from the metal surface when high energy
primary electrons strike on it.
Photoelectric emission: emission of electron from metal surface when radiation of
sufficient frequency strikes on the metal surface.

Properties of photons:
It is massless.
Energy of the photon is given by,

The momentum of photon is given by,

They do not get deflected by electric field and magnetic field.

They posses energy and momentum.

Limitations of classical theory of light-photoelectric effect :

According to wave theory, if more intensity beams of radiation are incident, then this
energy is transferred to the electrons and thus the energy of ejected electrons would be
high. But according to photon picture, energy is independent of intensity .
According to wave theory, high intensity beam can produce photoelectric effect and the
existence of threshold frequency is not explained.
It could not explain why photoelectric effect is instantaneous.
Einstein's explanation for photoelectric effect:
Einstein's photoelectric equation,

·
is the energy of the incident photon. It is completely absorbed by single electron and
hy

the electron will get ejected. Incident energy is used for: Ci) overcoming potential barrier
(ii) kinetic energy of ejected electron.

Explanation:
As intensity increases, the number of electrons emitted increases and thus photocurrent
increases.
From the equation it is clear that the kinetic energy is independent of intensity.
Minimum energy equal to the work function is required for photo electric effect take
place. Consequently, there exist a minimum frequency called threshold frequency below
which no photoelectric emission takes place.
Transfer of photon energy to electron is instantaneous, so there is no time lag in
photoelectric emission.

Rutherford's alpha ray scattering experiment / Geiger-Marsden experiment :

Rutheford's experimental result:
Most of the alpha particles were un-deflected
. through the gold foil
Some of the alpha particles were deflected
by a small angle

A very few alpha particles returned back

Alpha - particle trajectory: by 180°

Alpha particle closer to the nucleus has small

impact parameter and suffers larger scattering.
 Size of the nucleus:
Radius of the nucleus is given by the equation,

Density of nucleus:

Properties of nuclear force:

Short range force.Force is saturated and hence binding energy per nucleon remains
constant.
Strongest force.
Force is charge independent.

De-Broglie's explanation of Bohr's quantisation rule:

Electron in circular orbit should be seen as a particle wave.
Waves can produce standing waves under resonant conditions.
Standing waves are formed when the total distance travelled by the wave is an
integral multiple of its wavelength.

Depletion layer:

The region free from mobile charge carriers is known as depletion layer.
Potential barrier:
The potential across the p-n junction, which prevents the flow of majority charge
carriers across the junction is known as potential barrier.
Moving coil galvanometer:
Principle:
When a loop carrying current is placed in uniform magnetic field, it experiences a torque.

Construction and working:

Consists of a coil, with many turns free to rotate about fixed axis.
A cylindrical iron core is placed in radial magnetic field.
The iron core make the field radial and strengthens the magnetic field.
If the field is radial, then the torque acting will be maximum.

The torque acting on the coil is,

Conversion of galvanometer to ammeter:

Conversion of galvanometer to voltmeter:

Intrinsic semiconductor:

In intrinsic semiconductors, the number of free electrons is equal to the number of

holes . That is where is called intrinsic carrier concentration.
An intrinsic semiconductor will behave like an insulator at T = 0 K.
When temperature is increased,electrons gain thermal energy and move to conduction
band and leaves behind a hole in valence band.
Extrinsic semiconductor:

When a small amount, of a suitable

impurity(dopant) is added to the pure
semiconductor, the conductivity of the
semiconductor is increased manifold. Such
materials are known as extrinsic
semiconductors or impurity semiconductors and
the process is known as doping.
There are two types of dopants used in doping the
tetravalent Si or Ge:
(i) Pentavalent (valency 5); like Arsenic (As), Antimony (Sb),
Phosphorous (P), etc.
(ii) Trivalent (valency 3); like Indium (In), Boron (B),
Aluminium (Al), etc.
Ac generator:

Principle of working:
Rotating a coil in uniform magnetic field induces an emf - electromagnetic induction.
↑

Use: It is used to convert mechanical energy to electrical energy.

Construction:
It consists of a coil mounted on a rotor shaft.
The axis of rotation is perpendicular to the external uniform magnetic field.
The ends of the coil are connected to an external circuit by means of slip rings and brushes.

Working:
When a coil is rotated with a constant angular speed, the angle between the magnetic field and the
area vector of the coil changes, which results in change in magnetic flux. The change in magnetic flux
induces an emf in the coil.

·
Theory:

By Faraday's Law
,

S
E
-Md
=
N

N [BACOSO
=
-

NBAA[Cosco
= -

IIIII
E =
NBAc Sin (wt)
E =
Em Sin (cot)
t