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)

HUMAN EYE

The Various parts of eye and their functions 1. Cornea : It is a thin membrane through which light enters. It forms the transparent bulge on the front of eyeball. Most of the refraction occurs at the outer surface of the cornea.
 2. Eyeball : it is approximately spherical in shape, with a diameter of about 2.3cm.
 3. Iris : It is a dark muscular diaphragm that controls the size of pupil. It is behind the cornea.
 4. Pupil : It regulates and control the amount of light entering the eye. It is the black opening between aqueous humour & lens.
 5. Crystalline eye lens : Provide the focussed real & inverted image of the object on the retina. It is composed of a fibrous, jelly like material. This is convex lens that converges light at retina.

6. Ciliary muscles : It helps to change the curvature of eyelens and hence changes its focal length so that we can see the object clearly placed at different positon.
 7. Retina : Thin membrane with large no. of sensitive cells.
 8. When image formed at retina, light sensitive cells gets activated and generate electrical signal. These signals are sent to brain via optic nerue. Brain analyse these signals after which we perceive object as they are.

How pupil works ?

Here the pupil of an eye provide a variable aperture, whose size is controlled by iris a) When the light is bright : Iris contracts the pupil, so that less light enters the eye.
 b) When the light is din : Iris expand the pupil, so that more light enters the eye. Pupil open completely, when iris is relaxed

Persistence of Vision : It is the time for which the sensation of an object continue th in the eye. It is about 1/16 of a second.

Power of Accommodation : The ability of eye lens to adjust it focal length is called accommodation with the help of ciliary muscles.
DEFECTS OF EYE:

1. CATARACT : The image can not be seen distinctly because eye lens become milky and cloudy. This condition is known as cataract, it can cause complete or partial loss of vision. This can be corrected by surgical removal of extra growth (cataract surgery)

2. Myopia : (Near Sightedness) Aperson can see nearby object clearly, but cannot see distant object distinctly. Image formed in front of the retina. It is corrected by using a Concave Lens of appropriate power.

(3) Hypermetropia (Far - Sightedness) – Aperson cannot see nearby object clearly, but can see distant object distinctly. Image formed at a point behind the retina. It is corrected by using a Convex Lens of appropriate power.

4. Presbyopia As we become old, the power of accommodation of the eye usually decreases, the near point gradually recedes away. This defect is called Presbyopia. Person may suffer from both myopia and hypermetropia.
Correction- Using of Bifocal lens with appropriate power.

UNDERSTANDING THE EYE :
The eye functions in a similar way to a sophisticated camera. Light from an object will first pass through the cornea (the transparent dome at the front of the eye), which is the major focusing element of the eye and begins the process of bending (or refracting) the light rays. It then enters the front of the eye, which is filled with clear fluid called the aqueous humour; passes through the pupil, the round opening in the middle of the coloured iris until it reaches the lens, the fine focusing element of the eye. The lens completes the work started by the cornea by bending (refracting) the light rays so they focus at a single point on the retina. Behind the lens and in front of the retina is the main cavity of the eyeball, filled with a clear gel called the vitreous humour. The retina is made up of nerve tissue and is fed by a network of blood vessels (the choroid) supplying it with a constant source of oxygen and nutrients. Light falling on the retina causes impulses to be transmitted along the optic nerve and so that the brain can assemble a "clear picture". However, this will only occur if all the various components of the eye are in working order.
The lens is encased within a bag known as the capsule, which is suspended by delicate fibres called zonules. These zonules are the ligaments attaching the lens to the circular muscle ring, the ciliary body. Contraction of this muscle varies the tension on the lens capsule and allows the lens to become fatter so that the eye can change its focus for near vision. This process is called accommodation and allows the eye to see for reading. With advancing age the lens becomes harder and the ciliary muscle weaker and the ability of the eye to change its focus for near vision reduces. This is called presbyopia and is the reason that most people will require reading glasses after the age of 50. 

Glaucoma

What is Glaucoma?  Glaucoma comprises a group of eye diseases in which the pressure inside the eye (the intra-ocular pressure) causes damage to the nerve at the back of the eye (the optic nerve). This can result in a progressive loss of peripheral side vision (the visual field) and ultimately can cause complete blindness. In the majority of cases the intra-ocular pressure is raised. In some eyes, however, the pressure may be within normal limits, but damage still occurs because of weaknesses of the optic nerve.  Treatment of  Glaucoma  Medical - using eye-drops or tablets Laser-If treatment with drops fails to lower the eye pressure to a satisfactory level then laser treatments can be offered Surgical Corneal Grafting (Transplantation) A corneal graft or transplant is an operation in which part, or all, the cornea is removed and replaced with healthy corneal tissue from an individual who has died and donated their cornea for transplantation. CATARACTS  What is a Cataract? A cataract is an opacity or cloudiness that develops in the lens of the eye. The lens lies inside the eye behind the iris (the coloured part of the eye) and its central hole, the pupil. This cloudiness will restrict light from entering the back of the eye and reaching the retina and impair vision. If left untreated, cataracts will usually continue to develop until vision is completely obscured and the eye is blind. Symptoms of Cataract: Blurred vision - Changes to sight can include fuzziness and lack of clarity, with a washed out appearance.  Colour Reduction - Changes in the lens may lead to impairment of colour perception, particularly the loss of ability to see blues and purples. Night Blindness - The cloudiness of the lens allows less light to enter the eye, this increases difficulty in seeing at night or in dim light.

PERIODIC PROPERTIES : atomic size, ionisation enthalpy

Periodic Properties:

Atomic Radius
It is the distance from the centre of the nucleus to the outermost shell of electrons. Covalent
radius for an atom A in a
 molecule.

In general, the atomic size decreases on moving from left to right in a period due to increase in
effective nuclear charge and increases on moving from top to bottom in a group due to addition
of new shells.

van der Waals’ Radius
It is defined as one-half of the distance between the nuclei of two non – bonded isolated atoms
or two adjacent atoms belonging to two neighbOuring molecules of an element in the solid
state.
Metallic Radius
It is define as one-half of the distance between the centres of nuclei of the two adjacent atoms
in the metallic crystal.
onic Radius
An atom can be changed to a cation by losing of electrons and to an anion by gain of electrons.
A cation is always smaller than the parent atom because during its formation effective nuclear
charge increases and sometimes a shell may also decrease. On the other hand, the size of an
anton is always larger than the parent atom because during its formation effective nuclear
charge decreases.
In case of isoelectronic ions, r he higher the nuclear charge. smaller is the size. e.g., AI
3
<
Mg
2+
< Na
+
< f
-< O
2-< N
3-
covalent radius < metallic radius < van der Waals‟ radius

Ionisation Enthalpy (IE)
It is the amount of energy required to remove the loosely bound electron from the isol~ted
gaseous atom.
A(g) + IE → A
+
(g) + e
-Various factors with which IE depends

(i) Atomic size. varies inversely
(ii) Screening effect: varies inversely
(iii) Nuclear charge: varies directly
Generally left to right in periods ionisation enthalpy increases; down the group, it decreases.
IE values of inert gases are exceptionally higher due to stable configuration.
Successive ionisation enthalpies
IE
3 > IE
2 > IE
1
IE
1
of N is greater than that of oxygen due to stable half – filled 2p-orbitals.

DEFECTS IN MENDELEEFS TABLE

Defects in the Mendeleef’s Periodic Table
(i) Position of hydrogen Hydrogen has been placed in group IA (alkali metals). but it also
resembles with halogens of group VIlA. Thus. its position in the Mendeleef‟s Periodic Table is
controversial.
(ii) Position of isotopes As Mendeleef‟s classification is based on atomic weight, Isotopes
would have to be placed in different positions due to therr different atomic weights,
e.g.,
1
H1
2
H1
3
H1 would occupy different positions.
(iii) Anomalous positions of some elements Without any proper justification. in some cases
the element with higher atomic mass precedes the element with lower atomic mass. For
example, AI (atomic weight = 39.9) precedes K (atomic weight = 39.1) and similarly Co
(atomic weight. = 58.9) has been placed ahead of Ni (atomic weight = 58.7).
(iv) Position of Lanthanoids and actinoids Lanthanoids and actinoids were not placed in the
main Periodic Table.

Anomalous behaviour of the first element of a group. The first element of a group differs
considerably from its congeners (i.e., the rest of the elements of its group).
This is due to (i) small size (ii) high electronegativity and (iii) non availability of d·orbitals for
bonding. Anomalous behaviour is observed among the second row elements (i.e., Li to F)

Limitations of Long Form of Periodic Table
In the long form of the Periodic Table :
1. The position of hydrogen still remains uncertain.
2. The inner-transition elements do not find a place in the main body of the table. They are
placed separately.


Predicting the Position of an Element in the Periodic Table:
First of all write the complete electronic configuration. The principle quantum number of the
valence shell represents the period of the element.
Group of the element is predicted from the electrons present in the outermost (n) or penultimate
(n -1) shell as follows:

For s-block elements;
group number = number of ns-electrons
For p-block elements;
group number = 10 + number of ns and np electrons
For d-block elements;
group number = the sum of the number of (n -1) d
and ns electrons.
For f-block elements; group number is 3.