General Science for WBCS/RAIL/SSC/WBPSC Exam
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 a joule.
ENERGY
• Energy is a scalar quantity and its unit is Joule.
• The sum of all kinds of energies in an isolated system
remains constant at all times. This is the law of
conservation of energy.
POWER
Its unit is watt.
• 1 watt hour = 3600 Joule
• 1 kilowatt hour = 3.6 x 106
joule
• 1HP = 746 watt
GRAVITATION
• Everybody in the universe attracts other body by a
force called force of gravitation.
• The gravitational force of the earth is called gravity.
• 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'
• 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
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 Earth decreases.
• 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 1/6 of his actual
weight on the Earth.
SATELLITE
• 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 (34 minutes).
• Geo-stationary satellite revolves around the Earth at
a height 36000 km (approx).
• Time period of rotation of geo-stationary satellite is 24
hours.
• The Earth rotates on its axis from West to East. This
rotation makes the Sun and the stars appear to be
moving across the sky from East to West.
• A geosynchronous satellite is a satellite in
geosynchronous orbit, with an orbital period the same
as the Earth's rotation period.
• A special case of geosynchronous satellite is the
geostationary satellite, which has a geostationary
orbit – a circular geosynchronous orbit directly above
the Earth's equator.
• 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 800km (app.) Time periods of these
satellites is 84 min.
ATOMIC AND NUCLEAR PHYSICS
Cathode Rays
Cathode rays, discovered by Sir William Crooke
and its properties are
• travel in straight lines.
• Produce fluorescence.
• can penetrate through thin foils of metal and deflected
by both electric and magnetic fields.
• have velocity ranging 1/30th to 1/10th of the velocity of light
Positive or Canal Rays
• These rays were discovered by Goldstein.
• The positive ray consists of positively charged
particles.
• These rays travel in straight line.
• These rays are deflected by electric and magnetic
fields.
• These rays can produce ionization in gases.
X-Rays
• X-rays are electromagnetic waves with wavelength
range 0.1 A-100 A.
• X-rays were discovered by Roentgen.
• X-rays travels in straight line.
• Long exposures of X – rays in injurious for human
body.
• X – rays shows photoelectric effect.
Uses of X-Rays
• In medical sciences X-rays are used in surgery for
the detection of fracture, diseased organs, foreign
matter like bullet, stones etc. They are used in
treatment of cancer and in skin diseases.
• In Engineering, X-rays are used in detecting faults,
cracks, flaws and gas pockets in the finished metal
products and in heavy metal sheets.
• In Scientific Work, X-rays are used in studying
crystal structure and complex molecules.
• In Custom Department X-rays are used in custom
department for detection of banned materials kept
hidden.
Radioactivity
• Radioactivity was discovered by Henry Becquerel,
Madame Curie and Pierre Curie for which they
jointly won Nobel Prize.
Nuclear Fission
• Atom Bomb is based on nuclear fission. U235 and Pu239
are used as fissionable material.
• Nuclear fission was first demonstrated by Halin and
Fritz Strassmann.
Nuclear Fusion
• 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 bomb.
Nuclear Reactor or Atomic Pile
• Nuclear reactor is an arrangement, in which controlled
nuclear fission reaction takes place.
• 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 moderate.
Uses of Nuclear Reactor
(i)To produce electrical energy from the energy
released during fission.
(ii)To produce different isotopes, this can be used
medical, physical and agriculture science.
There are several components of nuclear reactor
which are as follows
• Fissionable Fuel U235 or U239 is used.
• 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.
NEWTON'S LAWS OF MOTION
• First Law: Everybody maintains its initial state of rest
or motion with uniform speed on a straight line unless
an external force acts on it. It is also called Galileo's
law or law of inertia.
Example While jumping from a slowly moving
train/bus one must run for short distance, in the
direction of motion.
• Second Law: The form acting on an object is directly
proportioned 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.
CIRCULAR MOTION
• When an object moves along a circular path, its
motion is called circular motion.
• The external force required to act radially inward over
the circular motion of the body is called Centripetal
force.
• Centrifugal force is such a pseudo force that. is
equal and opposite to Centripetal force.
• Cream separator, centrifugal dryer work on the principle of Centrifugal force.