In Physics, we study about a large number of quantities, which can be broadly classified into two categories : scalars and vectors.
Scalar Quantities Physical quantities
which have magnitude only. e.g. Mass,
speed, volume, work, time, power, energy,
etc. are scalar quantities.
Vector Quantities Physical quantities,
which have magnitude and direction both,
e.g., Displacement, velocity, acceleration,
force, momentum, torque, etc.
For a quantity to be a vector, it is necessary
that it follows the triangle rule of addition of
LAWS OF MOTION
First Law Every body maintains its initial
state of rest or uniform motion on a straight
line unless any external force acts on it. It is
also called Galileo’s law of inertia.
Example While jumping from a slowly
moving train/bus one must run for a short
distance, in the direction of motion.
Second Law The force acting on an object
is directly proportional to the product of the
mass of the object and the acceleration
produced on it.
Third Law To every action, there is an
equal and opposite reaction.
Example Bogies of the trains are provided
with buffers to avoid severe jerks during
shunting of trains.
Rocket moves up due to reaction of
downward ejection of gas.
● When an object moves along a circular
path, its motion is called circular
● The direction of motion at any point in
circular motion is given by the tangent
to the circle at that point.
● The external force required to act
radially inward over the circular motion
of the body is called centripetal force.
● In the death well, the walls of well exert
an inward force over the motorcycle
and as a reaction, the motorcycle exert
an outward force on the walls of the
● Centrifugal force is such a pseudo
force that is equal and opposite to
● Cream separator, centrifugal dryer work
on the principle of centrifugal force.
It is the opposing force that is set-up
between the surfaces of contact of two
bodies when one body slides or rolls or
tends to do so on the surface of another
● Due to friction we are able to move on
the surface of Earth.
● On applying brakes in automobile
● Work is said to be done, if force
acting on a body is able to actually
move it through some distance in the
direction of the force. Its SI unit is
Work = FS cos θ
where, F = force, S = displacement
and θ is the angle between the
direction of force and displacement.
● If θ > ° 90 , then work will be negative.
● If θ < ° 90 , then work will be positive.
● If θ = ° 90 , then work will be zero.
If a coolie carrying a load on his head is
moving on a horizontal platform, then
theoretically he is not doing any work
because θ = ° 90 ,W FS = ° = cos 90 0
Capacity of doing work by a body is
called its energy. Energy is a scalar
quantity and its unit is joule.
Mechanical energy is of two types.
● Kinetic Energy (K) Energy
possessed by a body due to its motion.
where, m is mass and v is the
● Potential Energy (U) The capacity
of doing work developed in a body
due to its position or configuration.
U = mgh
where, m is mass, g is acceleration
due to gravity and h is height.
● The sum of all kinds of energies in an
isolated system remains constant at
all times. This is the law of
conservation of energy.
Rate of doing work is called power. Its
unit is watt.
■ 1 watt hour = 3600 joule
■ 1 kilowatt hour = × 3 6 10 .
■ 1 HP = 746 watt
● Everybody in the universe attracts other
body by a force called force of gravitation.
● The gravitational force of the earth is called
● The acceleration produced in a body due to
force of gravity is called acceleration due to
gravity (g) and its value is 9.8 m s/ 2
● Acceleration due to gravity is independent of
shape, size and mass of the body.
● Escape velocity is the minimum velocity
with which an object just crosses the Earth’s
gravitational field and never returns. Escape
velocity at the Earth’s surface is 11.2 km/s.
● Escape velocity at the Moon’s surface is
2.4 km/s. Due to low escape velocity there is
no atmosphere on the Moon.
● Value of g decreases with height or depth
from Earth’s surface.
● g is maximum at poles.
● g is minimum at equator.
● g decreases due to rotation of Earth.
● g decreases if angular speed of Earth
increases and increases if angular speed of
● The acceleration due to gravity at the Moon
is one-sixth that of the Earth. So, the weight
of a person on the surface of the Moon will
be one-sixth of his actual weight on the
● Satellites are natural or artificial bodies
revolving around a planet under its
gravitational force of attraction.
● Moon is a natural satellite, while INSAT-B is
an artificial satellite of Earth.
● The period of revolution of satellite revolving
near the surface of Earth is 1 hour
24 minutes (84 minutes).
● Geo-stationary satellite revolves around the
Earth at a height of 36000 km (approx). The
orbit of geo-stationary satellite is called
parking orbit. Geo-stationary satellite revolves
in equatorial plane from West to East. Time
period of rotation of geo-stationary satellite is
● The Earth rotates on its axis from West to
East. This rotation makes the Sun and the
stars appears to be moving across the sky
from East to West.
● Geo-stationary satellite is used to telecast TV
programmes from one part of the world to
another, in weather forecasting, in
predictions of floods and droughts.
● Polar satellite revolves around the Earth in
polar orbit at a height of 800 km (approx).
Time period of these satellites is 84 min.
● These are used for weather forecasting,
Elasticity is the property of material of a body by
virtue of which the body acquires its original
shape and size after the removal of deforming
● A force, which changes the configuration of a
body, is called a deforming force.
● Steel is more elastic than rubber.
Pressure is defined as force acting normally on
a unit area of the surface.
Its unit is N/m2
. It is a scalar quantity.
● Atmospheric pressure is measured by an
instrument called the barometer.
● Sudden fall in barometric reading is the
indication of storm.
● Slow fall in barometric reading is the indication
● Slow rise in the barometric reading is the
indication of clear weather.
● The pressure exerted by liquid column at the
surface given as p hdg = , where d is the
density of liquid and h is height of liquid
column. In a static liquid at same horizontal
level, pressure is same at all points.
Pascal’s Law of Pressure
● If gravitational attraction is
negligible in equilibrium condition,
(approx) pressure is same at all
points in a liquid.
● The pressure exerted anywhere at a
point of confined liquid is
transmitted equally and
undiminished in all directions
throughout the liquid.
● Hydraulic lift, hydraulic press and
hydraulic brakes are based on the
Pascal’s law of pressure.
When a body is immersed partly or
wholly in a liquid, there is an apparent
loss in the weight of the body, which is
equal to the weight of liquid displaced
by the body.
● The weight of water displaced by an
iron ball is less than its own weight
whereas water displaced by the
immersed portion of a ship is equal
to its weight. So, small ball of iron
ball sink in water, but large ship float.
● A fat person will quickly learn the
swimming as compared to a slim
person because he will displace more
water. So, he will be more balanced.
● Hydrogen filled balloon float in air
because hydrogen is lighter than air.
● A person can lift more weight in
Laws of Floatation
A body floats in a liquid if
● The density of material of the body is
less than or equal to the density of
● When the density of material of the
body is equal to density of liquid, the
body floats fully submerged in liquid
in neutral equilibrium.
● When body floats in neutral
equilibrium, the weight of the body is
equal to the weight of displaced
liquid. The centre of gravity of the
body and centre of gravity of the
displaced liquid should be in one
vertical line for this condition.
● Density is defined as mass per unit
● Relative density is measured by hydro-
● The density of sea water is more than that
of normal water.
● When a ship enters in a sea from a river, it
raises a bit because the density of saline
water (salt water) is higher.
● The density of iron is more than that of
water, but less than that of mercury. So, a
solid chunk of iron sink in water but float
● If ice floating in water in a vessel melts, the
level of water in the vessel does not
● It is the force (F) acting normally on unit
length (l) of imaginary line drawn on
the surface of liquid i.e., T
= , its unit
● The property of a liquid by virtue of which
it tries to minimise its free surface area is
called the surface tension.
● Surface tension decreases with rise in
temperature and becomes zero at the
● The surface tension of clean water is
higher than that of a soap solution.
● Formation of lead shots, spraying result in
coldness, floatation of needle on water,
dancing of camphor on water, are based on
● Rain drop form spherical shape due to
● When kerosene oil is sprinkled on water,
its surface tension decreases, due to which
the excess of mosquitoes floating on the
surface of water die due to sinking.
Cohesive and Adhesive Forces
Force of attraction applied between molecules of
same substance is called cohesive force
while attractive force between molecules of
different substances is called adhesive
The phenomenon of rise or depression of
liquids in a capillary tube is called
■ A piece of blotting paper soaks ink because
the pores of the blotting paper serve as
■ The oil in the wick of a lamp rises due to
capillary action of threads in the wick.
■ The root hairs of plants draws water from
the soil through capillary action.
Viscosity is the property of a fluid by
virtue of which an internal frictional
force acts between its layers, when it is in
When an incompressible and
non-viscous liquid (or gas) flows in
streamlined motion from one place to
another, then at every point of its path
the total energy per unit volume
(pressure energy + kinetic energy +
potential energy) is constant.
Venturimeter, Atomizer, filter pump,
motion of aeroplane are based upon the
● Heat is a form of energy, which
measures the sensation or perception of
warmness or coldness of a body or
● Its units are calorie, kilocalorie or joule.
● 1 calorie = 4.18 joule.
● Temperature is the measurement of
hotness or coldness of a body.
● When two bodies are placed in contact,
heat always flow from a body at higher
temperature to the body at lower
A wave is a disturbance, which propagates
energy from one place to the other without
the transportation of matter.
Waves are broadly of two types
(i) Mechanical wave (longitudinal wave
and transverse wave)
(ii) Electromagnetic wave
In this wave, the particles of the medium
vibrate in the direction of propagation of
Waves on springs or sound waves in air are
examples of longitudinal waves.
In this wave, the particles of the medium
vibrate perpendicular to the direction of
propagation of wave.
Waves on strings under tension, waves on
the surface of water are the examples of
● The waves, which do not require medium
for their propagation i.e., which can
propagate even through the vacuum are
called electromagnetic waves.
● Light radio waves, X-rays, etc. are the
examples of electromagnetic waves.
These wave propagate with the velocity of
light in vacuum.
Sound waves are longitudinal mechanical
waves. Based on their frequency range
sound waves are divided into following
● The sound waves which lie in the
frequency range 20 Hz to 20000 Hz are
called audible waves.
● The sound waves having frequencies less
than 20 Hz are called infrasonic waves.
● The sound waves having frequencies
greater than 20000 Hz are called ultrasonic
● Ultrasonic waves are used for sending
signals, measuring the depth of sea,
cleaning machinery parts located in hard
to reach places, such as spiral tubes, etc.
Speed of Sound
■ Speed of sound is maximum in solids and
minimum in gases.
■ When sound goes from one medium to
another medium, its speed and wavelength
changes, but frequency remains unchanged.
■ The speed of sound remains unchanged by
the increase or decrease of pressure.
■ The speed of sound increases with the
increase of temperature of the medium.
■ The speed of sound is more in humid air than
in dry air because the density of humid air is
less than the density.
Echo The repetition of sound due to
reflection of sound waves, is called echo.
Intensity It is defined as the amount of
energy passing per unit time through a
unit area that is perpendicular to the
direction in which sound waves are
Pitch The sensation of a frequency is
commonly referred to as the pitch of a
SONAR It stands for sound navigation
and ranging. It is used to measure the
depth of a sea, to locate the enemy
submarines and shipwrecks.
If there is a relative motion between source
of sound and observer, the apparent
frequency of sound heard by the observer is
different from the actual frequency of
sound emitted by the source. This
phenomenon is called Doppler’s effect.
■ When the distance between the source and
observer decreases, then apparent
frequency increases and vice-versa.
● Light is a form of energy, which
is propagated as electromagnetic wave.
● It is the radiation which makes our eyes
able to see the object. Its speed is
× m/s. It is the form of energy. It is
a transverse wave. It takes 8 min 19 s to
reach on the Earth from the Sun and
the light reflected from Moon takes
1.28 s to reach Earth.
Reflection of Light
When a ray of light falls on a boundary
separating two media comes back into the
same medium, then this phenomenon is
called reflection of light.
Laws of Reflection
● The incident ray, reflected ray and the
normal to the reflecting surface at the
incident point all lie in the same plane.
● The angle of reflection is equal to the
angle of incidence.
Reflection from Plane Mirror
● The image is virtual and laterally
● The size of image is equal to that of
● If an object moves towards a plane
mirror with speed v, relative to the object
the image moves towards it with a speed
● To see his full image in a plane mirror, a
person requires a mirror of atleast half of
● The number of images formed by
two plane mirrors, inclined by an angle θ,
● Spherical mirrors are of two types
(i) Concave mirror (ii) Convex mirror
● Image formed by a convex mirror is
always virtual, erect and diminished.
● Image formed by a concave mirror is
generally real and inverted.
Uses of Concave Mirror
(i) As a shaving glass. (ii) As a reflector for the
headlights of a vehicle, search light. (iii) In
ophthalmoscope to examine eye, ear, nose by
doctors. (iv) In solar cookers.
Uses of Convex Mirror
(i) As a rear view mirror in vehicle because it
provides the maximum rear field of view and
image formed is always erect. (ii) In sodium
Refraction of Light
The bending of the ray of light passing from
one medium to other medium is called
refraction. When a ray of light enters from
one medium to other medium, its
frequency and phase do not change, but
wavelength and velocity change. Due to
refraction from Earth’s atmosphere, the
stars appear to twinkle.
Refractive index (µ)
Speed of light in vacuum
Speed of light in the medium
The angle of incidence in a denser medium
for which the angle of refraciton in rarer
medium becomes 90°, is called the critical
Total Internal Reflection (TIR)
If light is travelling from denser medium to
rarer medium and the angle of incidence is
more than the critical angle, then the light
is reflected back into the denser medium.
This phenomenon is called total internal
Sparkling of diamond, mirage and looming,
shinning of air bubble in water and optical fibre
are examples of total internal reflection.
It works on the principle of TIR. It is used
for telecommunication and various
medical purposes like endoscopy.
● Lens is generally of two types
(i) Convex lens (ii) Concave lens
● When lens is dipped in a liquid of higher
refractive index, the focal length
increases and convex lens behave as
concave lens and vice-versa.
● An air bubble trapped in water or glass
appears as convex, but behaves as
Dispersion of Light
● When a ray of white light is passed
through a prism, it gets splitted into its
constituent colours. This phenomenon
is called dispersion of light.
The different colours appeared in the
spectrum are in the following order,
violet, indigo, blue, green, yellow, orange
and red (VIBGYOR).
● Rainbow is formed due to dispersion of
sunlight by water droplets.
● Wavelength of red colour is maximum
and for violet colour is minimum.
● Red, green and blue are primary colours.
Green and magenta, blue and yellow, red
and cyan are complementary colours.
Scattering of Light
● When light passes through a medium in
which particles are suspended whose
sizes are of the order of wavelength of
light, then light striking on these particles
deviated in different directions. Scattering
of light is maximum in case of violet
colour and minimum in case of red
● Blue colour of sky is due to scattering of
blue and violet light. The brilliant red
colour of rising and setting sun is also due
to scattering of light.
● It is an optical instrument like camera. It
forms the real image of the object on
retina of the eye. Least distance of distinct
vision is 25 cm.
A short-sighted eye can see
only nearer objects. Distant
objects are not seen clearly.
This defect can be removed
by using concave lens of
suitable focal length.
A long sighted eye can see
distant objects clearly but
nearer object are not clearly
visible. This defect can be
removed by using a convex
Presbyopia In this defect both near and
far objects are not clearly
visible. It can be removed by
using bi-focal lens.
Astigmatism In this defect eye cannot see
horizontal and vertical lines
clearly. This defect can be
removed by using suitable
● Simple microscope is a convex lens of
small focal length.
● Compound microscope is a
combination of two convex lenses,
called objective lens and eyepiece,
separated by a distance.
● Astronomical Telescope is also a
combination of two lenses in which
objective lens is a convex lens of large
aperture and large focal length while
eye-piece is a convex lens of small
aperture and small focal length.
Charge is the basic property associated with
matter due to which it produces and
experiences electric and magnetic effects.
Similar charges repel each other and
opposite charges attract each other. The SI
unit of charge is coulomb.
Conductor Conductors are those materials,
which allow electricity to pass
through themselves. Metals like
silver, iron, copper and earth acts
like a conductor. Silver is the best
Insulator Insulator are those materials which
do not allow electricity to flow
through themselves. Wood, paper,
mica, glass, ebonite are insulators.
● Electric current is defined as the rate of
flow of charge or charge flowing per unit
time. Its unit is ampere. It is a scalar
● A lightning conductor is fixed on tall
buildings to protect them from the
destructive effects of the lightning.
● An electric bulb produces a bang when it
is broken because there is a vacuum
inside the electric bulb, when the bulb is
broken air rushes at great speed from all
sides to fill the vacuum. The rushing of
air produces a noise generally referred
to as the bang.
● Radioactivity was discovered by Henry
Becquerel, Madame Curie and Pierre
Curie for which they jointly won Nobel
● The nucleus having protons 83 or
more are unstable. They emit α β, and
γ particles and become stable. The
elements of such nucleus are called
radioactive elements and the
phenomenon of emission of α β, and γ
particles is called radioactivity.
● Robert Pierre and his wife Madame
Curie discovered a new radioactive
● The end product of all natural
radioactive elements after emission of
radioactive rays is lead.
● With the emission of an α-particle,
atomic number is decreased by 2 and
mass number is decreased by 4.
● With the emission of a β-particle,
atomic number is increased by 1 and
mass number does not change.
● The nuclear reaction, in which a
heavy nucleus splits into two nuclei of
nearly equal mass is nuclear fission.
1 U + → + n 56 36 Ba Kr 141 92+ 30n
● Atom Bomb is based on nuclear
235 and Pu239 are used as
● Nuclear fission was first
demonstrated by Hatin and Fritz
● When two or more light nuclei
combined together to form a heavier
nucleus is called as nuclear fusion.
● For the nuclear fusion, a temperature
of the order of 108 K is required.
● Hydrogen Bomb was made by the
American Scientist in 1952. This is
based on nuclear fusion. It is
1000 times more powerful than atom
Nuclear Reactor or Atomic Pile
● Nuclear reactor is an arrangement, in
which controlled nuclear fission reaction
● First nuclear reactor was established in
Chicago University under the supervision
of Prof Enrico Fermi.
● Heavy water, graphite and beryllium oxide
are used to slow down the fast moving
neutrons. They are called moderator.
● The cold water, liquid oxygen, etc. are used
as coolant to remove heat generated.
● Cadmium or boron rods are good absorber
of neutrons and called the control rods.
Uses of Nuclear Reactor
(i) To produce electrical energy from the
energy released during fission.
(ii) To produce different isotopes, which
can be used in medical, physical and
There are several components of nuclear reactor
which are as follows
■ Fissionable FuelU
239 is used.
■ Moderator Moderator decreases the energy
of neutrons, so that they can be further used for
fission reaction. Heavy water and graphite
are used as moderator.
■ Control Rod Rods of cadmium or boron are
used to absorb the excess neutrons produced in
fission of uranium nucleus, so that the chain
reaction continues to be controlled.
■ Coolant A large amount of heat is produced
during fission. Coolant absorbs that heat and
prevents excessive rise in the temperature. The
coolant may be water, heavy water or a gas like
He or CO2
LASER (Light Amplification by Stimulated Emission of Radiation)
It is a device that produces an intense,
coherent and highly directional beam of the
single frequency. It can be transmitted over a great distance without being spread.
LASER Technology in India
In 1964, the first laser as Gallium Arsenide
(GaA) semi-conductor laser was designed and
fabricated by Bhabha Atomic Research Centre (BARC).
Various Institutions as CAT (Centre for Advanced Technology), DRDO (Defence
Research and Development Organisation) and Indian Institute of Science work on the
laser plasma, quantum optics, etc., are going to work with American collaboration.
MASER (Microwave Amplification by Stimulated Emission of Radiation)
It was invented by three American scientist Gordon, Gieyer and H Townes in 1952.
It uses microwaves in amplified form of longer wavelength of the light, while ordinary laser uses light.