CLASS XI..PHYSICS..SOLIDS, ELASTICITY..

Elasticity:

Elasticity is that property of the object by virtue of which it regain its original configuration 

after the removal of the deforming force.

Elastic Limit: Elastic limit is the upper limit of deforming force upto which, if deforming force is removed, the body regains its original form completely and beyond which if deforming force is increased the body loses its property of elasticity and get permanently deformed

Perfectly Elastic Bodies-Those bodies which regain its original configuration immediately and completely after the removal of deforming force are called perfectly elastic bodies. e.g., quartz and phosphor bronze .

Stress

The internal restoring force acting per unit area of a deformed body is called stress.

Stress = Restoring force / Area

Its unit is N/m

2

or Pascal and dimensional formula is [ML

-1

T

-2

].

Stress is a tensor quantity.

Tangential Stress -If deforming force is applied tangentially, then the stress is called 

tangential stress.

Strain

The fractional change in configuration is called strain.

Strain = Change in the configuration / Original configuration

It has no unit and it is a dimensionless quantity.

(1) Longitudinal strain= Change in length / Original length

(2) Volumetric strain = Change in volume / Original volume

(3) Shearing strain = Angular displacement of the plane perpendicular to the fixed surface.

Hooke’s Law

Within the limit of elasticity, the stress is proportional to the strain.

1. Young’s Modulus of Elasticity

It is defined as the ratio of normal stress to the longitudinal strain Within the elastic limit.

y = Normal stress / Longitudinal strain

y = FΔl / Al = Mg Δl / πr

2

l

Its unit is N/m

2

or Pascal and its dimensional formula is [ML

-1

T

-2

].

2. Bulk Modulus of Elasticity -It is defined as the ratio of normal stress to the volumetric strain within the elastic limit.

K = Normal stress / Volumetric strain

K = FV / A ΔV

Its unit is N/m

2

or Pascal and its dimensional formula is

3. Modulus of Rigidity (η)

It is defined as the ratio of tangential stress to the shearing strain, within the elastic limit.

η = Tangential stress / Shearing strain

Its urut is N/m

2

or Pascal and its dimensional formula is [ML

-1

T

-2

].

Compressibility-

Compressibility of a material is the reciprocal of its bulk modulus of elasticity.

Compressibility (C) = 1 / k

Its SI unit is N

-1

m

2

and CGS unit is dyne

-1

cm

2

.Limit of Elasticity-

The maximum value of deforming force for which elasticity is present in the body is called its 

limit of elasticity.

Breaking Stress-

The minimum value of stress required to break a wire, is called breaking stress.

Breaking stress is fixed for a material but breaking force varies with area of cross-section of the 

wire.

Safety factor = Breaking stress / Working stress

Elastomers-

The materials for which strain produced is much larger than the stress applied, with in the limit 

of elasticity are called elastomers, e.g., rubber, the elastic tissue of aorta, the large vessel 

carrying blood from heart. etc.

Elastomers have no plastic range.

Poisson’s Ratio

When a deforming force is applied at the free end of a suspended wire of length 1 and radius R, 

then its length increases by dl but its radius decreases by dR. Now two types of strains are 

produced by a single force.

(Write math exp from text)

Relation Between Y, K, η and σ

(i) Y = 3K (1 – 2σ)

(ii) Y = 2 η ( 1 + σ)

(iii) σ = 3K – 2η / 2η + 6K

(iv) 9 / Y = 1 / K + 3 / η or Y = 9K η / η + 3K

Cantilever

A beam clamped at one end and loaded at free end is called a cantilever.

Depression at the free end of a cantilever is given by

δ = wl

3

/ 3YI

G

CLASS 8 SCIENCE SOLAR SYSTEM

1.Which of the following is NOT a member of the solar system?
(a) An asteroid
(b) A satellite
(c) A constellation
(d) A comet
A.(c) Constellation

constellation is not a member of the solar system. Constellations are groups of stars that form recognisable shapes.

2.Which of the following is NOT a planet of the sun?

(a) Sirius
(b) Mercury
(c) Saturn
(d) Earth

A.a) Sirius
3.Phases of the moon occur because
(a) we can see only that part of the moon which reflects light towards us.
(b) our distance from the moon keeps changing.
(c) the shadow of the Earth covers only a part of the moon’s surface.
(d) the thickness of the moon’s atmosphere is not constant.

 A.(a) Phases of the moon occur because we can see only that part of the moon which reflects light towards us

4.Fill in the blanks:

(a) The planet which is farthest from the sun is _________.

(b) The planet which appears reddish in colour is _________.

(c) A group of stars that appear to form a pattern in the sky is known as a __ _________.

(d) A celestial body that revolves around a planet is known as a _________.

(e) Shooting stars are actually not _________.

(f) Asteroids are found between the orbits of ________ __ and _________.

 A.a) The planet which is farthest from the sun is __Neptune__.

(b) The planet which appears reddish in colour is __Mars__.

(c) A group of stars that appear to form a pattern in the sky is known as a __constellation__.

(d) A celestial body that revolves around a planet is known as a satellite_.

(e) Shooting stars are actually not stars __.

(Shooting stars are not stars, they are meteors)

(f) Asteroids are found between the orbits of __Mars __ and __Jupiter.

(Asteroids occupy a large gap between the orbits of Mars and Jupiter)

5.In which part of the sky can you find Venus if it is visible as an evening star?

A..in the western sky after sunset and is called the evening star.
6.What is a constellation? Name any two constellations.
A..A constellation is a group of stars that form a recognisable pattern in the sky. The two well known constellations are Ursa Major and Orion.(DRAW FROM TEXT)

7. Define asteroids & mateors

A..

i) Asteroids

A collection of a large number of small objects, gases and dust are revolving around the sun. They occupy a large gap between the orbits of Mars and Jupiter. However, these are not planets. These celestial objects are known as asteroids.

(ii) Meteors

Meteors are small celestial objects that are seen as bright streaks of light in the sky.

They brunt out on entering the Earth’s atmosphere because of the heat produced by friction. This results in bright streaks in the sky. They are not planets.

8.Explain how you can locate the Pole Star with the help of Ursa Major

A..In order to locate the Pole star in the sky, first of all Ursa Major or Big Dipper constellation mustbe located. The bowl of the Big Dipper consists of four bright stars Consider two stars at the end of this bowl. Now, draw an imaginary straight line towards the Northern direction connecting these two stars (as shown in the given figure).

This imaginary line meets a star called the Pole Star. The length of the imaginary line from the bowl is about five times the distance between the two stars of the bowl.

9.Do all the stars in the sky move? Explain
A..No. The Earth rotates from West to East on its axis. Hence, all stars in the sky (except the Pole star) appear to move from East to West. With reference to the Earth, the Pole star does not appear to move in the sky because it is located above the axis of rotation of the Earth in the north direction. It appears to remain stationary at a point in the sky

10..Why is the distance between stars expressed in light years? What do you understand by the statement that a star is eight light years away from the Earth?
A..The distance of the stars from the Earth and the distance between the stars are very large. It is inconvenient to express these distances in kilometer (km). Thus, these large distances are expressed in light years. One light year is the distance travelled by light in one year. One light year is equal to 9.46 × 10¹² km.

A star is located eight light years away from the Earth. This means that the distance between the star and the Earth is equivalent to the distance travelled by light in eight years, i.e., a star is located 8 × (9.46 × 10¹²) = 7.6 × 10¹³ km away from the Earth.

11.

CLASS 8-SCIENCE Q&A..LIGHT

1.Differentiate between regular and diffused reflection. Does diffused reflection mean the failure of the laws of reflection?
ANS: Regular reflection takes place from a smooth or a regular surface. In regular reflection, all reflected rays are parallel to each other for parallel incident rays. Irregular or diffused reflection takes place from an irregular surface. In diffused reflection, the reflected rays are not parallel to each other for parallel incident rays.

2.State the laws of reflection.
Ans:(i) The angle of reflection is always equal to the angle of iincidence.

(ii) The incident ray, the reflected ray and the normal to the reflective surface at the point of incidence all lie in the same plane.

3.Draw a labelled sketch of the human eye.

4.Why Laser light is harmful for the human eyes

Ans: Laser light is harmful for the human eyes, because its intensity is very high. It can cause damage to the retina and lead to blindness. Hence, it is advisable not to look at a laser beam directly.

Chemistry --structure of atom

Bohr’s model for hydrogen atom:-

Postulates for Bohr’s model:

 1.ectron in hydrogen atom move around nucleus in circular path of fixed radius and energy. these paths are called orbits.  

Energy of e does not change with time.

However, when electron move from lower to higher stationary state it absorbed sub amount of energy and energy release when it comes back.

3.     Frequency of radiations emitted or absorbed when transition of e occur is given by

Where, e1 & e2 is lower & higher energy state.

4.     Angular momentum of n electron in given stationary state is given by 

[Where n =1,2,3.....]

Limitation of Bohr’s model:-

1.     Bohr model fail to explain finer detail of hydrogen atom spectrum observed by spectroscopic, techniques.

2.     It fails to explain spectrum of other atom except hydrogen atom.

3.     It fails to explain splitting of the spectral lines in presence of electric (stark effect) or magnetic field ( Zeeman effect )

4.     Fell to explain formation of molecules from atoms by chemical bonding.

Dual behaviour of matter :-De-broglie explained that matter also behave like radiation and exhibit dual behavior means both like particle and wave like properties .

Relation

   Where  l =  wavelength.

             m = mass of particle ,

             v = velocity

p = momentum

Heisenberg’s uncertainty principle:- He explain that it is impossible to determine simultaneously the exact positive and exact momentum (or velocity) of an electron

Mathematical explanation(see text)

Aufbau principle   :- 

                              According to this principle in the ground state of the atoms the orbital’s are filled in order of their increasing energies means electrons enter higher energy orbital’s  so order in which orbital’s are filled is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p.

Pauli exclusion principle  :-

Two electrons in an atoms can’t have same set of 4-quantum no.

·        Only two electrons may exist in same orbital and these electrons must have opposite spin.

Hund’s  rule of maximum multiplicity :-.According to this rule pairing of  electron in the orbital’s belonging to the same sub-shell (p, d or f)

 Does not take place until each orbital belonging to that sub-shell has got one electron each i.e. it is singly occupied.

CHIMISTRY-STRUCTURE OF ATOM

Cathode ray discharge tube experiments: - 

1.     Cathode rays start from cathode and move toward anode.

2.     These rays are not visible but there behaviour can be observed with fluorescent or phosphorus sent material.

3.     In the absence of magnetic or electric field these travels in strait lines

4.     In the presence or magnetic or electric field the behaviour of cathode.

Cathode rays (electrons) do not depend on  the martial of the electrode and  nature of the gas tin the tube so electro us are basic constituent of all atoms.

 

Mass of electron

 From charge on e^- & e/m_e

 We get,                  

             M_e = 9.1094 ´ 10^-31 kG

DISCOVERY OF NEUTRON:

Discovered by Chadwick (1932).

  By bombarding a thin sheet of beryllium by alpha particles.

  Electrically neutral particles were emitted known as neutrons.

Rutherford’s nuclear model of atom

When beam of high energy α- particles was directed at gold foil then tiny flash of light observed at photographic plate.

Rutherford observed that-

1)    Most of the α-  practical  passed  through gold foil undeflected :

2)    A small fraction of α- particles was deflected by small angles.

3)    A very few α- particles (about 1 in 20000) bounced back means deflected by nearly 180⁰

^{CONCLUSION :}

1)    Most of space in atom is empty because most of α- particles passed 

undeflected.

2)    Few +ve charged α- particles were deflected.

Because + ve charge of the atom present in center in very small volume that repelled & deflected the +ve charged α- particles.

3)    Volume of nucleus is negligible as compared to total volume of atom

On the basis of observation &  conclusion Rutherford proposed model:

1)    +ve charge & most of mass present in the center of atom known as nucleus.

2)    Electrons moves around nucleus with very high speed in circular paths known as orbits.

3)    Electrons and nucleus (protons) are held together by electrostatic force of attraction 

Atomic number (Z) = no of protons in the nucleus of an atom

                                       = no of electrons in a neutral atom

Mass number (A) = number of protons (z) + number of electron (n)

Isobars :- 

              These are atoms with same mass number but different atomic no.

Isotopes: - 

               These are atoms with same atomic number but  different atomic mass no.

Planck’s Quantum theory:

Energy (E) of  quantum of  radiation is directly proportional to its frequency(n)

 i.e.            E=hn

Where,      h = planks constant = 6.626× 10^-34 js

Photo electric effect:-When a beam of light strike a metal surface then electrons were ejected. This phenomena is known as photo electric effect.

Number of electron ejected is directly proportional to intensity (or brightness) of light

     There is characteristic minimum frequency (n₀threshold frequency) below which photoelectric effect is not observed.

    If n > n₀ then electrons comes out with kinetic energy which increases with increase in frequency of light.

Kinetic energy of ejected electrons is given by-

h n = h n₀+ ½(m_eV²)