Integrated Guidance Programme of General Studies for IAS
(Pre) - 2013
Subject - General Science
Chapter : Gist of Physics from NCERT Books
- An atom is the smallest particle of the element that can exist
independently and retain all its chemical properties.
- Dalton’s atomic theory, which suggested that the atom was indivisible
and indestructible. But the discovery of two fundamental particles
(electrons and protons) inside the atom, led to the failure of this aspect
of Dalton’s atomic theory.
Thomson proposed that:
- An atom consists of a positively charged sphere and the electrons are
embedded in it.
- The negative and positive charges are equal in magnitude. So, the atom
as a whole is electrically neutral.
- Rutherford’s alpha-particle scattering experiment led to the discovery
of the atomic nucleus. Rutherford’s model of the atom proposed that a very
tiny nucleus is present inside the atom and electrons revolve around this
nucleus. The stability of the atom could not be explained by this model.
- Neils Bohr’s model of the atom was more successful. He proposed that
electrons are distributed in different shells with discrete energy around
the nucleus. If the atomic shells are complete, then the atom will be stable
and less reactive.
- J. Chadwick discovered presence of neutrons in the nucleus of an atom.
So, the three sub-atomic particles of an atom are: (i) electrons,
(ii) protons and (iii) neutrons. Electrons are negatively charged, protons
are positively charged and neutrons have no charges. The mass of an electron
is about 1/2000 times the mass of an hydrogen atom. The mass of a proton and
a neutron is taken as one unit each.
- Isotopes are atoms of the same element, which have different mass
- Isobars are atoms having the same mass number but different atomic
Radioactivity occurs when an atomic nucleus breaks down
into smaller particles. There are three types of nuclear radiation: alpha,
beta, and gamma. Alpha particles are positively charged, beta particles are
negatively charged, and gamma particles have no charge. The radiations also
have increasing levels of energy, first Alpha, then Beta, and finally Gamma,
which is the most energetic of all these. Alpha and Beta are particles, but
Gamma is a wave.
- When a radioactive nucleus changes, the remaining nucleus (and atom) is
not the same as it was. It changes its identity.
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- Fission is the splitting of an atom. Not all atoms will go through
fission; as a matter of fact, very few do under normal circumstances.
- Fusion is the process of two small atomic nuclei coming together to make
a larger nucleus which is stable. The simplest nuclei to use are deuterium
and tritium (isotopes of hydrogen).
- Temperature is a relative measure, or indication of hotness or coldness.
- Heat is the form of energy transferred between two (or more) systems or
a system and its surroundings by virtue of temperature difference. The SI
unit of heat energy transferred is expressed in joule (J) while SI unit of
temperature is kelvin (K), and °C is a commonly used unit of temperature.
- Thermometer is a device used for measuring temperatures. The two
familiar temperature scales are the Fahrenheit temperature scale and the
Celsius temperature scale. The Celsius temperature (tC) and the Farenheit
temperare (tF) are related by: tF = (9/5) tC + 32
- In principle, there is no upper limit to temperature but there is a
definite lower limit- the absolute zero. This limiting temperature
is 273.16° below zero on the celsius scale of temperature.
LIGHT TRAVELS ALONG A STRAIGHT LINE
- Light is reflected from all surfaces. Regular reflection takes place
when light is incident on smooth, polished and regular surfaces.
After striking the surface, the ray of light is reflected
in another direction. The light ray, which strikes any surface,is called the
incident ray. The ray that comes back from the surface after reflection is
known as the reflected ray.
- The angle between the normal and incident ray is called the angle of
incidence . The angle between the normal and the reflected ray is known as
the angle of reflection.
- Two laws of reflection are:
- The angle of incidence is equal to the angle of reflection.
- Incident ray, reflected ray and the normal drawn at the point of
incidence to the reflecting surface, lie in the same plane.
- Lenses are widely used in spectacles, telescopes and microscopes. Those
lenses which feel thicker in the middle than at the edges are convex lenses.
Those which feel thinner in the middle than at the edges are concave lenses.
Notice that the lenses are transparent and light can pass through them.
- A convex lens converges (bends inward) the light generally falling on
it. Therefore, it is called a converging lens. On the other hand, a concave
lens diverges (bends outward) the light and is called a diverging lens.
- A concave lens always forms erect, virtual and smaller image than the
Total Internal Reflection:
Total internal reflection is the phenomenon which
involves the reflection of all the incident light off the boundary. Total
internal reflection only takes place when both of the following two
conditions are met: (i) the light is in the more dense medium and
approaching the less dense medium., and (ii) the angle of incidence is
greater than the so-called critical angle. Total internal reflection will
not take place unless the incident light is traveling within the more
optically dense medium towards the less optically dense medium.
Dispersion of Light:
- It is the phenomenon of splitting of a beam of white light into its
constituent colors on passing through prism. The order of colors from the
lower end are violet, indigo, blue, green, yellow, orange and red. At one
end of the band, there is red and at the other violet. The sequence of
colours can be best remembered by the wordVIBGYOR’ which is formed by taking
the initial letter of each colour.
- A laser is just a really powerful beam of light. Laser isn’t a word but
an acronym. It stands for LIGHT AMPLIFICATION by STIMULATED EMISSION of
Magnetism and Electricity:
The word magnet is derived from the name of an island in Greece
calledMagnesia where magnetic ore deposits were found, as early as 600 BC.
Magnetite, an iron ore, is a natural magnet. It is called lodstone.
The properties of a magnet are
- it attracts small piece of iron towards it.
- it always cmes to rest in north-south direction when suspended freely.
- like poles repel, unlike poles attracts each other
- Magnetic poles always exist in pairs.
- the strength of a magnet is maximum at poles located near the poends
- The phenomenon due to which a suitable combination of bodies on rubbing,
get electrified is called electricity. If a charge on a body is not allowed
to flow, it is called the static electricity.
- There are two different types of electric charges namely the positive
and negative charges. Like charges repel and unlike charges attract each
Electric current always flows from the point of high
potential. The potential difference between two conductors is equal to the
work done in conducting a unit positive charges from one conductor to the
other conductor through a metalic wire.
The flow of charge is called the current and it is the
rate at which electric charges pass though a conductor. The charged particle
can be either positive or negative. In order for a charge to flow, it needs
a push (a force) and it is supplied by voltage, or potential difference. The
charge flows from high potential energy to low potential energy.
- The branch of physics which deals with the relationship between
electricity and magnetism is called electomagnetism.
- Faraday’s law of induction is one of the important concepts of
electricity. It looks at the way changing magnetic fields can cause current
to flow in wires. Basically, it is a formula/concept that describes how
potential difference (voltage difference) is created and how much is
created. It’s a huge concept to understand that the changing of a magnetic
field can create voltage.
- Coulomb’s Law is one of the basic ideas of electricity in physics. The
law looks at the forces created between two charged objects. As distance
increases, the forces and electric fields decrease. This simple idea was
converted into a relatively simple formula. The force between the objects
can be positive or negative depending on whether the objects are attracted
to each other or repelled.
- Motion: In physics, motion is change of location or position of
an object with respect to time. Mechanical motion is of two types,
transitional ( linear ) and rotational ( spin).
- SPEED: The speed of a moving body is the rate at which it covers
distance i.e. the distance it covers per unit of time.
- VELOCITY: The distance covered by an object in a specified
direction in unit time interval is called velocity. The S.I. Unit of
velocity is m/s.
- ACCELERATION: When an object’s velocity changes, it accelerates.
Acceleration shows the change in velocity in a unit time. Velocity is
measured in meters per second, m/s, so acceleration is measured in (m/s)/s,
or m/s2, which can be both positive and negative. The symbol for
acceleration is a (boldface).
Newton’s Laws of Motion:
1. Newton’s First Law of Motion:
2. Newton’s Second Law of Motion:
- The acceleration of an object as produced by a net force is directly
proportional to the magnitude of the net force, in the same direction as the
net force, and inversely proportional to the mass of the object.
3. Newton’s Third Law of Motion:
- For every action, there is an equal and opposite reaction.
The statement means that in every interaction, there is a
pair of forces acting on the two interacting objects. The size of the forces
on the first object equals the size of the force on the second object. The
direction of the force on the first object is opposite to the direction of
the force on the second object. Forces always come in pairs - equal and
opposite action-reaction force pairs.
Properties of Matters:
According to kinetic theory of matter:
- molecules are in the state of continuous motion in all possible
directions and hence they posses kinetic energy which increases with the
gain of heat energy or rise in temperature,
- the molecules always attract each other,
- the force of attraction between the molecules decreases with the
increase in intermolecular spaces
- Sound is a form of energy and like all other energies, sound is not
visible to us. It produces a sensation of hearing when it reaches our ears.
Sound can not travel through vacuum.
Sound is produced due to vibration of different
objects.The matter or substance through which sound is transmitted is called
a medium. It can be solid, liquid or gas. Sound moves through a medium from
the point of generation to the listener.
- sound waves are longitudinal waves. Sound travels as successive
compressions and rarefactions in the medium. In sound propagation, it is the
energy of the sound that travels and not the particles of the medium.
The audible range of sound for human beings extends from
about 20 Hz to 20000 Hz (one Hz = one cycle/s). Children under the age of
five and some animals, such as dogs can hear up to 25 kHz (1 kHz = 1000 Hz).
- Sounds of frequencies below 20 Hz are called infrasonic sound or
- Frequencies higher than 20 kHz are called ultrasonic sound or
ultrasound. Ultrasound is produced by dolphins, bats and porpoises.
Units and Measurement:
Each base quantity is defined in terms of a certain
basic, arbitrarily chosen but properly standardised reference standard
called unit (such as metre, kilogram, second, ampere, kelvin, mole and
candela). The units for the fundamental or base quantities are called
fundamental or base units.
Other physical quantities, derived from the base
quantities, can be expressed as a combination of the base units and are
called derived units. A complete set of units, both fundamental and derived,
is called a system of units.
The SI units have well defined and internationally
accepted unit symbols (such as m for metre, kg for kilogram, s for second, A
for ampere, N for newton etc.). Physical measurements are usually expressed
for small and large quantities in scientific notation, with powers of 10.
Scientific notation and the prefixes are used to simplify measurement
notation and numerical computation, giving indication to the precision of
SI Base Quantities and Units:
- When a body is immersed fully or partially in a fluid, it experiences an
upward force that is equal to the weight of the fluid displaced by it.
Archimedes’ principle has many applications. It is used
in designing ships and submarines. Lactometers, which are used to determine
the purity of a sample of milk and hydrometers used for determining density
of liquids, are based on this principle.
- Density and Relative Density: The mass per unit volume of a
substance is called its density. The SI unit of density is kilogram per
meter cubed. Density= mass/volume.
- The relative density of a substance is the ratio of its density to that
of water: Relative density = Density of a substance/Density of water. Since
the relative density is a ratio of similar.
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