LECTURE -2 : CLASS VIII : SCIENCE : CHAPTER 3 : SYNTHETIC FIBRES & PLASTICS

CLASS VIII   |    SCIENCE    |    CHAPTER 3

      notes prepared by subhankar Karmakar

                                                                         

POLYESTER:

Polyester is a synthetic fibre in which the polymer units are linked by ester groups. Terylene is a popular polyester fibre. The chemical compounds used in making polyester fibres are made from petroleum products called petrochemicals. Both Nylon and polyester are thermoplastic polymers. Therefore, most of the properties of polyester fibres are similar to those of Nylon. There are some differences between nylon and polyester fibres. 

Properties of polyester fibres:

1. Polyester fibre is stronger than nylon fibres.

2. Polyester fibres are also softer than nylon fibres. 

3. Polyester fabric is strong, wrinkle resistant, easy to wash and dry, not attacked by moths and ordinary chemicals and has high abrasion resistance. These properties makes it suitable for making dress material. 

4. Polyester can be blended with natural fibres like cotton or wool and known as polycot (terrycot)  and polywool (terrywool) respectively. 

Uses of polyester fibres:

1. The most important use of polyester is in making fabrics for sarees, dress materials and curtains.

2. Polyester is used for making sails of sailboats. Polyester sails are light, strong, do not stretch and and do not rot in contact with water. 

3. Polyester is used for making water hoses for fire fighting operations.

4. Polyester is used for making conveyor belts.

PET:

PET is a very familiar form of polyester. PET is the abbreviation of the synthetic polymer called Poly Ethylene Terephthalate. PET can be made into a fibre or a plastic. When used as a fibre PET generally referred to as polyester, while the term PET is usually used for the plastic form. 

Properties of PET: 

1. PET as a plastic is very lightweight. 

2. It is naturally colourless with high transparency. 

3. PET is strong and impact resistant. 

4. PET is shatterproof and hence it is used to make bottles, jars, and utensils.

5. PET bottles are used for fizzy drinks and PET jars are used for sugar, salt, rice etc.

6. It is also used to make thin films.

ACRYLIC:

Acrylic is a synthetic fibre. Acrylic fibre is made from a chemical called acrylonitrile by the process of polymerization. 

Characteristics of acrylic:

1. Acrylic is lightweight, soft and warm with a wool-like feel. 

2. Acrylic retains its shape, resists shrinkage and wrinkles. 

3. It can be dyed very well. 

4. Acrylic fibres are strong and durable. 

5. Acrylic absorbs very little water so it has "quick-dry" quality. 

6. Acrylic fibres are resistant to moths and most chemicals. 

Uses of acrylic fibres:

1. Due to its wool-like feel, acrylic fibre is often used as a substitute for wool. 

2. The wool obtained from natural sources like sheep is quite expensive. Acrylic offers a less expensive alternative to natural wool. So, the clothes made from acrylic are relatively cheaper but more durable than those made from natural wool. 

3. Many of the sweaters which the the people wear in winter, and the shawls and blankets which people use, are actually not made from natural wool, though they appear to be made from wool. They are made from synthetic fibre called acrylic. 

4. Acrylic fibre is used for making sweaters shawls blankets jackets sportswear, socks, furnishing fabrics, carpets and as lining for boots and gloves.

LECTURE -1 : CLASS VIII : SCIENCE : CHAPTER 3 : SYNTHETIC FIBRES & PLASTICS

CLASS VIII   |    SCIENCE    |    CHAPTER 3

      notes prepared by subhankar Karmakar

                                                                         

Definition

                                                                                  

FIBRES: A very thin, thread-like strand from which cloth is made, is called a fibre. Fabric means cloth. Fabric is made by weaving or knitting long, twisted threads called 'yarn' made from fibres. The clothes which we wear are made of fabrics. Fabrics are made from fibres obtained from 'natural' or artificial' sources (synthetic sources). Thus, all the fibres can be divided into two groups:

(1) Natural fibres, and (ii) Synthetic fibres.

NATURAL FIBRES:

The fibres obtained from plants and animals are called natural fibres. Cotton, flax, jute, wool and silk are natural fibres. Cotton, flax and jute fibres come from plants whereas wool and silk come from animals.

SYNTHETIC FIBRES: 

The synthetic fibres are made by human beings. Rayon, nylon, polyester and acrylic are synthetic fibres.

FIBRES ARE MADE OF POLYMERS: 

POLYMER: A polymer is a 'very big molecule' formed by the combination of a large number of small molecules.

The small molecules (of chemical compounds) which join together to form a polymer are called 'monomers'. 

The monomers which make a polymer may all be of the same compound' or of 'two different compounds'.

So, a polymer is made of many small 'repeating units' (of chemical compounds) called monomers.

Polymers are of two types :

Natural polymers and Synthetic polymers. 

NATURAL POLYMERS:

Cotton, wool and silk are natural polymers. For example, cotton fibre is made of a natural polymer called cellulose. Cellulose is a polymer which is made up of a large number of small glucose molecules (or glucose units) joined one after the other. The walls of all the plant cells are made up of cellulose. So, wood contains a large amount of cellulose polymer. Thus, polymers occur in nature too. 

SYNTHETIC POLYMERS:

Nylon, polyester, acrylic, polythene, polyvinyl chloride (PVC), bakelite, and melamine are synthetic polymers (or man-made polymers). For example, nylon fibre is made up of nylon polymer in which two different types of molecules (or monomer units) are combined alternately to form long chains.

                                                                                  

SYNTHETIC FIBRES: 

a. PRODUCTION OF SYNTHETIC FIBRES: 

The man-made fibres produced from chemical substances are called synthetic fibres, Synthetic fibres are made in industry by the chemical process called 'polymerisation'. A synthetic fibre is a long chain of small units joined together. Each small unit is a chemical compound (called organic compound). Many, many such small units join together one after the other to form a very large single unit called polymer. It is this man made polymer which forms synthetic fibres. Thus, a synthetic fibre is a polymer made from the molecules of a monomer (or sometimes two monomers) joined together to form very long chains. Synthetic fibres are also known as man-made fibres or artificial fibres.

b. TYPES OF SYNTHETIC FIBRES:

Depending upon the type of chemicals used for manufacturing synthetic fibres, there are four major types of synthetic fibres (or man-made fibres). These are :

1. Rayon, 

2. Nylon, 

3. Polyester, and 

4. Acrylic.

c. RAYON IS NOT FULLY SYNTHETIC:

Rayon is a man-made fibre made from a natural material called cellulose (obtained from wood pulp).

WOOD PULP: 

Wood pulp is a soft, wet mass of fibres obtained from wood. Wood pulp contains a large amount of natural polymer called 'cellulose'.

d. FULLY SYNTHETIC FIBRES:

Nylon, polyester and acrylic are fully synthetic fibres which do not require a natural material (like cellulose) for their manufacture. These fully synthetic fibres are prepared by a number of processes by using raw materials (or chemical compounds) of petroleum origin, called petrochemicals.

RAYON & ITS CHARACTERISTICS:

Rayon is often regarded as artificial silk. It is a man-made fibre prepared from a natural raw material (called cellulose) by chemical treatment. The cellulose required for making rayon is obtained from 'wood pulp'. So, we can also say that is obtained by the chemical treatment of wood pulp (which contains cellulose). 

• PRODUCTION OF RAYON: 

Rayon is produced as follows:

(i) Wood pulp is dissolved in an alkaline solution (sodium hydroxide solution) to form a sticky liquid called 'viscose'.

(ii) Viscose is forced to pass through the tiny holes of a metal cylinder (called spinneret) into a solution of sulphuric acid when a silk like thread of rayon is formed.

• RAYON IS NOT FULLY SYNTHETIC FIBRE:

Since rayon is made from naturally occurring polymer (cellulose) present in wood pulp, therefore, rayon is neither a fully synthetic fibre nor a fully natural fibre. It is a semi-synthetic fibre. Rayon is different from truly synthetic fibres because it is obtained from a natural material (wood pulp).

• RAYON, THE ARTIFICIAL SILK:

Although rayon is obtained from a natural resource called wood pulp, yet it is said to be a man-made fibre. This is because it is obtained by the chemical treatment of wood pulp in factories. Rayon fibre is chemically identical to cotton but it has shine like silk. Since rayon resembles silk in appearance, therefore, rayon is also called artificial silk. 

• ADVANTAGES OF RAYON:

Rayon is cheaper than natural silk and can be woven like silk fibres. Rayon can also be dyed in a variety of colours.

• USES OF RAYON:

1. Rayon is used in textile industry for making clothing like sarees, blouses, dresses, socks, etc.

2. Rayon (mixed with cotton) is used to make furnishings such as bed-sheets, curtains, blankets, etc.

3. Rayon (mixed with wool) is used to make carpets.

4. Rayon is used in medical field for making bandages and surgical dressings.

5.  Rayon is used in tyre industry for the manufacture of tyre cord.

NYLON & ITS CHARACTERISTICS:

Nylon is a synthetic fibre. In fact, nylon is the first fully synthetic fibre made by man without using any natural raw materials (from plants or animals). It was made in the year 1931. 

• SOURCE OF NYLON: 

The chemical compounds (or monomers) used in making nylon are now obtained from petroleum products called petrochemicals. It is made up of the repeating units of a chemical called an 'amide'. So, nylon is a polyamide (which is a polymer). 

The name NYLON comes from the fact that it was developed in New York (NY) and London (LON). 

Nylon is a thermoplastic polymer (which can be melted by heating). Molten nylon is forced through the tiny holes in a spinneret to make nylon fibres (or nylon threads), or cast into desired shapes.

• PROPERTIES OF NYLON: 

Some of the important properties of nylon fibres are as follows: 

(i) Nylon fibres are very strong fairly elastic, lightweight and lustrous. 

(ii) Nylon fibres absorb very little water, so clothes made of nylon are easy to wash and dry. 

(iii) Nylon is wrinkle resistant. 

(iv) Nylon fibres have high abrasion resistance (high wear and tear resistance), so they are very durable (long lasting). 

(v) Nylon is not attacked by moths and ordinary chemicals.

Due to all these properties, nylon fibres have become very popular for making clothes.

• USES OF NYLON:

1. Nylon is used for making textiles (fabrics) like sarees, shirts, neck-ties, tights, socks and other garments.

2. Nylon is used in making curtains, sleeping bags and tents.

3. Nylon is used in making ropes, car seat belts, fishing nets, tyre cord, strings for sports rackets and musical instruments, bristles for toothbrushes and paint brushes. 

4. Nylon is used for making parachutes and ropes for rock climbing. 

5. Nylon is used as a plastic for making machine parts.

"All these uses of nylon are due to the high strength of nylon it is actually stronger than a steel wire of similar thickness."

LECTURE -3 : CLASS VIII : SCIENCE : CHAPTER 8 : CELLS, TISSUES, ORGANS, ORGAN SYSTEMS AND ORGANISM

CLASS VIII   |    SCIENCE    |    CHAPTER 8

      notes prepared by subhankar Karmakar

                                                                                  

1. CELLS: 

A cell is the smallest unit of life which has a definite structure and performs a specific function. 

All the cells of a multicellular organism are not similar. They are of many different shapes and sizes. Most of the cells are specialised to perform particular functions. They are called specialised cells. For example, in animals, muscle cells are specialised to contract and relax so that they can bring about movement in body parts. In plants, photosynthetic cells are specialised to carry out photosynthesis and make food. There are many types of specialised cells in animals and plants which perform different functions.

2. TISSUES:

The group of similar cells which work together to perform a particular function is called a tissue. For example, in animals, muscle tissue specialised to contract and relax so as to move body parts. Therefore, muscle tissue brings about movement in the body parts of animals. In plants, photosynthetic tissue is a group of photosynthetic cells joined together which is specialised to do photosynthesis and make food. There are many different types of tissues in both, animals as well as in plants. 

3. ORGANS:

An organ is a collection of different tissues which work together to perform a particular function in the body of an organism.

The multicellular organisms are made up of different organs which do different jobs for the organism. Some of the organs in animals are: 

Heart, Stomach, Brain, Lungs, Kidney, etc.

Some of the organs in plants are:

Roots, Stem, Leaf, Flower etc.

Each organ does different specialised work. 

Like in animals, 

a. The function of heart is to pump blood around the body.

b. The function of brain is to control all the parts of the body.

c. The function of lungs is to take in oxygen and give out carbon dioxide.

d. The function of the stomach is to digest the food.

In plants, 

a. The function of the roots is to absorb water and dissolve mineral salts from the soil.

b. The function of stem is to carry water and minerals from the roots to the leaves and the prepared food from the leaves to other parts of the plant.

c. The function of a leaf is to prepare food for the plant by the process of photosynthesis.

d. The flowers are reproductive organs which led to the formation of fruits and seeds. The fruit protects the seeds.

4. ORGAN SYSTEMS:

A group of interconnected organs which works together to do a big job for the organism, is called an organ system. 

All the multicellular animals and plants have many organ systems in their bodies to carry out various life processes. 

For example, the various organ systems of animals are:

Digestive system, respiratory system, circulatory system, nervous system, excretory system, reproductive system, muscular system and skeletal system. 

The plants have two main organ systems:

Root system and shoot system.

Work of the organ systems:

The function of digestive system is to break down the food into simple substances which can be absorbed by the body. The main organs of the digestive system are:

Mouth, Oesophagus, stomach, small intestine, large intestine, rectum and anus. 

5. ORGANISM:

An organism is an animal or a plant which can exist on its own. An organism is made up of many different organ systems which work together to perform all the functions necessary for maintaining life.

Multicellular organisms are built like in the following sequence. 

1. Cells make up tissues

2. Tissues make up organs

3. Organs make up organ systems

4. Organ systems makeup an organism

LECTURE: 1 : CLASS XI: PHYSICS : UNITS & MEASUREMENTS

CLASS XI   |    PHYSICS    |    CHAPTER 2

      notes prepared by subhankar Karmakar

PHYSICAL QUANTITIES:

All those quantities which can be measured directly or indirectly and in terms of which the laws of Physics can be expressed are called physical quantities. For example, length, mass, time, speed, temperature, force, electric current, angle etc are physical quantities.

TYPES OF PHYSICAL QUANTITIES:

Physical quantities are of two types:

a. Fundamental quantities

b. Derived quantities

a. FUNDAMENTAL QUANTITIES:

The physical quantities which can be treated as independent of other physical quantities and are not usually defined in terms of other physical quantities are call fundamental quantities. There are seven fundamental quantities, and two supplementary fundamental quantities.

The fundamental or base quantities are:

1. Mass

2. Length

3. Time

4. Electric current

5. Thermodynamic temperature

6. Luminous intensity

7. Amount of substance

Two supplementary fundamental quantities are:

1. Angle

2. Solid angle

b. DERIVED QUANTITIES:

The physical quantities who's defining operations are based on other physical quantities are called derived quantities. All physical quantities other than fundamental quantities are derived quantities. For example, velocity, speed, acceleration, force, momentum etc are derived quantities.

THE MEASURING PROCESS:

Measurement: The measurement of a physical quantity is the process of comparing this quantity with a standard amount of the physical quantity of the same kind, called its unit. 

The measurement of a physical quantity has two components.

1. The unit in which the quantity is measured (u)

2. The numerical value or the magnitude of the quantity. (n)

If the measure of a physical quantity = Q

Numerical value of the physical quantity = n

Size of the unit = u, then

Q = nu

If n₁ and n₂ are the numerical values for a physical quantity Q corresponding to the units u₁ and u₂ , then

Q = n₁u₁ =  n₂ u₂

PHYSICAL UNIT:

The standard amount of a physical quantity chosen to measure the physical quantity of the same kind is called a physical unit.

Desirable characteristics of a physical unit:

1. It should be well defined.

2. It should be of convenient size. Neither too small, nor too large.

3. It should not change with time.

4. It should be easily reproducible.

5. It should be imperishable or indestructible.

6. It should not be affected by the change in physical conditions such as variation of pressure temperature etc.

7. It should be internationally acceptable.

8. It should be easily accessible.

FUNDAMENTAL & DERIVED UNITS:

Fundamental units: The physical units which can neither be derived from one another, nor they can be further resolved into more simpler units are called fundamental units. Units of fundamental quantities are fundamental units.

Derived units: All the other physical units which can be expressed in terms of the fundamental units are call derived units. Like unit of force is Newton, but it can be expressed in terms of fundamental units.

Force = Mass x acceleration

1 N = 1 kg x 1 m /s² = 1 kg m /s²

DIFFERENT SYSTEM OF UNITS:

a. cgs system = It was set up in France. It is based on centimetre, gram and second as the fundamental units of length, mass and time respectively.

b. mks system = It is also a French system based on metre, kilogram and second as the fundamental units of length, mass and time respectively.

c. SI system = It is the international system of units. What is the modernization extended form of the mks system. 

BASIC SI QUANTITIES AND UNITS:

Basic quantity - basic unit - symbol

1. Length - metre - m

2. Mass - kilogram - kg

3. Time - second - s

4. Temperature - kelvin - K

5. Electric Current - ampere - A

6. Luminous Intensity - candela - cd

7. Quantity of matter - mole - mol

Supplementary units

1. Angle - radian - rad

2. Solid angle - steradian - sr

Definition of Radian and Steradian:

1. Radian: it is defined as the plane angle subtended at the centre of a circle by an Arc equal in length to the radius of the circle.

θ (in radians) = arc/radius = l/r

2. Steradian: it is defined as the solid angle subtended at the centre of a sphere why the surface of the sphere equal in area to that of a square having each side equal to the radius of the sphere. 

Ω (in steradian) = surface area/ radius²

Some common practical units:

1. Fermi = it is also known as femtometre. It is a very small unit of distance. It is used to measure nuclear distance. The radius of a proton is 1.2 fermi.

1 fermi = 10⁻¹⁵ m

2. Angstrom (Å): 

It is also a small unit of distance. It is used express wavelength of light.

1 Å = 10⁻¹⁰ m = 10⁻⁸ cm

3. Nano-metre:

It is also used to express wavelength of light.

1 nano metre = 10⁻⁹ m

4. Micron (μm)

It is also known as micro metre. 

1 μm = 10⁻⁶ m

5. Astronomical Unit ( AU)

It is defined as the the mean distance of the earth from the sun. It is a practical unit used for measuring large distances. It is used in astronomy to measure distances of planets.

1 AU = 1.496 x 10¹¹ m

6. Light year (ly)

It is the distance travelled by light in vacuum in one year. Light year is used in astronomy to measure distances of nearby stars. Like alpha centauri, the nearest are outside the solar system is 4.3 light years away from the Earth.

1 ly = 9.467 x 10¹⁵ m

7. Parsec or Parallactic Second:

It is the largest practical unit of distance used in astronomy. It is defined as the distance, at which an Arc of length 1 astronomical unit subtends an angle of 1 second of arc. 

1 parsec = 3.26 ly = 3.08 x 10¹⁶ m

Indirect method for measuring large distances:

a. Triangulation method for the height of an inaccessible object.

b. Parallax method to measure the distance of a nearby star. 

* Sextant: sextant is an instrument by which we can measure the angle of a distant object with the horizontal.

a. Triangulation method for the height of an inaccessible object.

Let AB = h be the height of the mountain to be measured. By using a sextant, we first measure the angle of elevation of its peak from my point C on the ground. Let it be θ₁ or ∠ACB  =  θ₁  . Move the sextant to another position D such that CD = d. Again measure the angle of elevation, ∠ADB = θ₂ . 

in right triangle ∆ABC, 

cot  θ₁ = CB/AB = x /h

in right triangle ∆ABD, 

cot  θ₂ = DB/AB = (d + x )/h

cot  θ₂ -  cot  θ₁ = (d + x )/h - x/h = d/h

∴ h = d / ( cot  θ₂ -  cot  θ₁ )

Hence, if we know d , the height h can be determined.

b. Parallax method

Parallax: parallax is the apparent shift in the position of an object with respect to another when we shift our eye side wise.

suppose we hold a pen O at a distance S from the eyes. Look at the pen first by the left eye L closing the right eye, and then buy the right eye R closing the left eye. The position of the  pen appears to change with respect to the background. This is called parallax. The distance between the two points of observation is called basis. In this case, the distance LR = b between the two eyes is the basis. ∠LOR = θ is called parallax angle or parallactic angle.

Parallax method can be used to find the

1. Distance of moon or any other planet.

2. Distance of a nearby star. 

1. Distance of moon or any other planet.

To measure the distance S of the moon or a faraway planet P, we observe it simultaneously from two different positions (observatories) A and B on the earth, separated by a large distance AB = b. We select a distant star S' whose position and direction can be taken approximately same from A and B. 

      Now, ∠PAS' = Φ₁ and ∠PBS' = Φ₂ are measured from the two observatories at the same time. As b<<S, so we can take AB as an arc of length b. 

      Now  θ = Arc/Radius = b/s

                      ∴ S = b/θ

where θ = ∠APB = Φ₁ + Φ₂ , is the parallactic angle. 

2. Distance of a nearby star. 

Suppose N is a nearby star whose distance d from the earth is to be found. F is a far off star whose direction and position is fixed for all the position of the earth in its orbital motion. When the earth is at position A, the parallax angle between distance star F and nearby star N is determined. Let it be θ₁ . After 6 months, the earth is at diametrically opposite position B. The parallax angle ∠NBF = θ₂ is measured. 

Total parallax angle subtended by N on the earth's orbital diameter AB is 

                θ = θ₁ +  θ₂

As,           θ = Arc/Radius

                θ = AB/d

             ∴ d = AB/θ

This Parallax method is useful for measuring distances of stars which are less than 100 light years away from the Earth. 

LECTURE -2 : CLASS VIII : SCIENCE : CHAPTER 8 : CELL STRUCTURE & FUNCTIONS

CLASS VIII   |    SCIENCE    |    CHAPTER 8

      notes prepared by subhankar Karmakar

Comparison of Plant Cells and Animal Cells:

* A General diagram of a plant cell

* A general diagram of an animal cell

The main similarities between plant cells and animal cells are given below:

1. Plant cells and animal cells have a cell membrane or plasma membrane around them.

2. Plant cells and animal cells have cytoplasm.

3. Plant cells and animal cells have a nucleus.

4. Plant cells and animal cells have a nuclear membrane.

5. Plant cells and animal cells have mitochondria.

The main differences between plant cells and animal cells are given below:

1. A plant cell has a cell wall around it, but an animal cell does not have a cell wall around it.

2. A photosynthetic plant cell has chloroplasts in it. Other plant cells have different plastids in them, but in an animal cell there is no chloroplasts or other plastids.

3. A plant cell has a large vacuole in it, but an animal cell usually does not have any vacuole, some animal cells have small vacuoles.

Prokaryotic cells and Eukaryotic cells:

a. Prokaryotic cells and prokaryotes:

The primitive cells, where nucleus of the cell is not properly organised and they do not have any nuclear membrane around the nuclear material and they are called prokaryotic cells. In prokaryotic cells, the nuclear material is in direct contact with the cytoplasm.

The organisms made of prokaryotic cells are called prokaryotes. 

 All the prokaryotes are simple, unicellular organisms. Most of the bacteria and blue green algae are prokaryotes. 

 b. Eukaryotic cells and Eukaryotes:

The cells having nuclear material enclosed by a nuclear membrane are called Eukaryotic cells. Eukaryotic cells have a proper, well organised nucleus and nucleus are separated from the cytoplasm by nuclear membrane. Eukaryotic cells are more advanced then prokaryotic cells. 

The organisms which are made of Eukaryotic cells are called Eukaryotes. All the organisms other than bacteria and blue green algae are Eukaryotes. For example, Amoeba is an Eukaryote. Eukaryotes may be unicellular or multicellular. 

Different organisms having variety in cell number, cell shape and cell size:

A. Variety in the number of cells:

Different organisms have different number of cells in their bodies.

B. Variety in shape of cells:

The cells in multicellular organisms have many different shapes.

C. Variety in size of cells:

The cells in multicellular organisms can have many different sizes.

A. Variety in the number of cells:

Depending on the number of the cells, in the body of an organism, an organism is called unicellular or multicellular. 

(i) Unicellular Organisms:

The organisms which are made up of only one cell are called unicellular organism. It is also known as single celled organism. Some of the examples of unicellular organisms are:

Amoeba, Paramecium, Euglena, Chlamydomonas and bacteria.

The single cell of all the unicellular organisms behaves as a complete organisms. A unicellular organism can perform all the necessary life functions with the help of just one cell. For example, Amoeba is a tiny animal which consists of only one cell but can perform all the basic functions of life like taking food, digestion, respiration, movement, response to environmental changes, removal of waste and reproduction etc. 

(ii) Multicellular Organisms:

The organisms which are made up of many cells are called multicellular organisms. Most of the plants and animals around us, including us are multicellular organisms. Multicellular organisms millions and billions of cells which vary in shapes and sizes. Different groups of cells perform a variety of functions. A multicellular organism starts its life as a single cell called fertilized egg cell or Zygote. 

B. Variety in shape of cells:

There are many types of cells in the bodies of multicellular organisms. These cells differ in shapes. For example, the shape of nerve cell in animals is very different from the shape of a muscle cell. A nerve cell is long and branched whereas a muscle cell is pointed at both ends and has a spindle shape and an epithelial cell is rectangular shape. Cells are different in shapes and sizes so that they can perform different functions. Some of the examples of animal cells which have different sizes and shapes are: nerve cell or neuron, muscle cell, epithelial cell, red blood cell, white blood cells, bone cell and cartilage cell. 

Different shape of a cell helps in its functioning. Like nerve cells are long and have projections so that they can make contacts with many other Nerve cells and carry messages over long distances like between brain and other parts of body. Muscle cells bring about the moment at body parts by contracting and relaxing, hence, they are pointed at the both ends and spindle shaped. 

Some of the important plant cells are: epidermal cells, xylem cells, phloem cells, and photosynthetic cells. The epidermal cells form a layer around the plant organs and protect the cells below from injury, xylem cells are the tube like plant cells having thick and strong walls which carry water and mineral salts from the roots of the plant to the leaves. Phloem cells are also tubelight plant cells having thin walls which carry the food made by leaves to all other parts of the plant. The photosynthetic cells of the plant contain chlorophyll and prepare food by photosynthesis. The mesophyll cells of leaf are the photosynthetic plant cells. These cells in the leaf of a plant are specially adapted for making food by photosynthesis. 

Amoeba: 

All the plant and animal cells are not capable of independent existence, the single celled organism like amoeba can exist independently. 

The shape of amoeba cell is irregular. In fact the Amoeba cell has no fixed shape. The 

Amoeba cell keeps on changing its shape continuously. Shape of Amoeba cell changes because amoeba can make its cytoplasm in any direction it wants to. The Amoeba cell finger like projections of varying lengths protruding out of his body which is called pseudopodia. 

Amoeba derives two advantages by changing shape: 

The changing of shape due to the formation of pseudopodia helps amoeba in 

1. movement

2. In capturing food.

C. Variety in size of cells:

The cells are of many different sizes. Some are so small that they cannot be seen with the naked eyes, whereas large cells also exists. Generally most of the cells are extremely small in size, like bacteria cells have a length of 0.1 micrometer ~ 0.5 micrometer. The smallest cell is bacteria mycoplasma, which is only 0.1 micrometre long. Whereas, the birds eggs are very large cells, they can be seen easily with naked eye. Each egg of the bird is a single cell, like the hen's egg is a single cell. The biggest cell is the ostrich egg which is approximately 17 cm long. The size of cells has no relation with the size of the body of an animal. Rather it is related to its function. 

LECTURE 1 : CLASS XI: PHYSICS : MOTION IN ONE DIMENSION

CLASS XI   |    PHYSICS    |    CHAPTER 3

      notes prepared by subhankar Karmakar

Rest : An object is said to be at rest if it does not change its position with respect to its surroundings with time.

Motion: An object is said to be in motion if it changes its position with respect to its surroundings with time.

Distance / path length: (s or x)

It is the length of the actual path travelled by a body between its initial and final positions. It is a scalar quantity.

The SI unit of distance is metre

The CGS unit of distance is centimetre

Displacement: (s or x)

The displacement of an object is the change in the position of an object in a fix direction. It is a vector quantity.

The SI unit of displacement is  metre 

The CGS unit of displacement is centimetre

Speed: (v)

The distance travelled per unit time is called speed. 

Speed = distance travelled/ time taken

         v = s/t

It is a scalar quantity

The SI unit of speed is m/s or ms⁻¹

The CGS unit of speed is cm/s or cms⁻¹

The dimensional formula of speed is [M⁰L¹T⁻¹]

Velocity: (v) 

The rate of change of position of an object which time in  a given direction is called its velocity.(v)

Velocity= displacement/time

It is a vector quantity.

SI unit of velocity is m/s

CGS unit of velocity is cm/s

The dimensional formula of velocity is [M⁰L¹T⁻¹]

Acceleration: 

The rate of change of velocity of an object with time is called its acceleration. (a)

Acceleration= change in velocity/time taken

It is a vector quantity.

The SI unit of acceleration is m/s²

The CGS unit of acceleration is cm/s²

The dimensional formula of acceleration is [M⁰L¹T⁻²]

Different types of speed

There are four types of speed

1. Uniform speed

2. Variable speed

3. Average speed

4. Instantaneous speed

Uniform speed: if a body covers equal distances in equal intervals of time the body is said to be in uniform speed.

Variable speed: if a body covers unequal distances in equal intervals of time the body is in variable speed.

Average speed: the ratio of Total distance travelled and total time taken is called average speed

Instantaneous speed: the speed of an object at any particular instant of time is called instantaneous speed of that object.

Different types of velocity:

There are basically four types of velocity

1. Uniform velocity

2. Variable velocity

3. Average velocity

4. Instantaneous velocity

Uniform velocity: a body is said to be moving with uniform velocity if it covers equal displacements in equal intervals of time.

Variable velocity: a body is said to be moving with variable velocity if either its speed changes or direction of motion changes or or both change with time

Average velocity: the ratio of total displacement and total time is called average velocity

Instantaneous velocity: the velocity of an object at a particular instant of time or at a particular point of its path is called its instantaneous velocity.

How to calculate average speed in different situations:

a. A body covering different distances with different speeds:

Suppose a body covers distances s₁, s₂, s₃.... with speeds v₁, v₂, v₃... respectively, then its average speed will be

vₐ = (s₁+ s₂ + s₃... )/(t₁ + t₂ + t₃... )

⟹ vₐ =  (s₁+ s₂ + s₃... )/(s₁/v₁ + s₂/v₂ +  s₃/v₃ .....)

(i) if s₁ = s₂ = s

vₐ =  (s₁+ s₂)/(s₁/v₁ + s₂/v₂)

⟹ vₐ = (s + s)/(s/v₁ + s/v₂)

⟹ vₐ = (2s)/s(1/v₁ + 1/v₂)

⟹ vₐ = (2v₁v₂)/(v₁ + v₂)

As an example suppose a body travels from A to B at 40 m/s and from B to A at 60 m/s. Calculate the average speed.

Soln. Here the distances of same ie.  s₁ = s₂ = s

As AB distance = BA distance

∴  vₐ = (2v₁v₂)/(v₁ + v₂)

    ⟹ vₐ = (2x40x60)/(40 + 60)

    ⟹ vₐ = (2x40x60)/100

    ⟹ vₐ = 48 m/s

b. A body moving with different speeds in different time intervals:

Suppose a body travels with speeds v₁, v₂, v₃, ...

In time intervals   t₁,  t₂,  t₃ .......

Respectively, then

Total distance travelled = v₁t₁ +  v₂t₂ + v₃t₃ + .....

Total time taken = t₁ + t₂ + t₃ + ........

∴  vₐ = (v₁t₁ +  v₂t₂ + v₃t₃ + .....)/( t₁ + t₂ + t₃ + ..)

As an example, if a body travels along a straight line for the first 10 minutes with speed 30 km/h, and the next 20 minutes with speed 60 km/h. Find the average speed of the body.

Soln. Here,  v₁ = 30 km/h; v₂ = 60 km /h

t₁ = 10 min = 10/60 h = 1/6 h

t₂ = 20 min = 20/60 h = 2/6 h

∴  t₁ + t₂ = 1/6 + 2/6 = 3/6 = 1/2 h

We know,  vₐ = (v₁t₁ +  v₂t₂)/( t₁ + t₂)

∴  vₐ = {30x(1/6)+60x(2/6)}/(1/2)

⟹ vₐ = (5 + 20)/(1/2)

⟹ vₐ = 25x2 = 50 km/h

CLASS XI: PHYSICS : CHAPTER-1 : PHYSICAL WORLD

CLASS XI   |    PHYSICS    |    CHAPTER 1

      notes prepared by subhankar Karmakar

Q1. What is scientific method? Mention the various steps involved in it.

Ans. Scientific method: the step-by-step approach used by a scientist in studying natural phenomena and establishing laws which govern these phenomena is called scientific method. 

Generally, it involves the following steps:

a. Taking a large number of systematic observations by doing controlled experiments.

b. Studying these observations and making qualitative and quantitative reasoning.

c. Suggesting mathematical models to account for the observed behaviour.

d. Predicting new phenomena on the basis of suggested model.

e. Modifying the theory, if necessary, the light of fresh evidences.

Q2. Name the four basic forces in nature. Arrange them in the order of their increasing strengths.

Ans. Fundamental forces in nature: 

In the macroscopic world, we observe several kinds of forces. All the forces between microscopic objects arise from two fundamental forces:

a. Gravitational force(F_g) 

b. Electromagnetic force. (F_e)

In the microscopic world, there are two more basic forces:

c. Strong nuclear force(F_s)

d. Weak nuclear force (F_w)

(F_g) : (F_w) : (F_e) : (F_s) = 1: 10²⁵ : 10³⁶ : 10³⁸

Q3. Describe briefly the fundamental forces in nature.

Ans. There are four fundamental forces in nature. They are as follows:

a. Gravitational force(F_g) 

b. Electromagnetic force. (F_e)

c. Strong nuclear force(F_s)

d. Weak nuclear force (F_w)

Gravitational force(F_g) : it is a force of mutual attraction between two bodies by virtue of their masses. According to the Newton's law of gravitation, the gravitational attraction between two bodies of masses m₁ and m₂ separated by a distance r is given by

   F_g = Gm₁m₂/r²

Where G is the universal gravitational constant.

Electromagnetic force (F_e): 

The force acting between two electric charges at rest is called electrostatic force. Electrostatic force is a part of electromagnetic force. According to Coulomb's law, the magnitude of the electrostatic force (F_e) between two point charges q₁ and q₂ separated by a distance r in vacuum is given by

(F_e) = (1/4πεₒ).q₁q₂ / r²

Where εₒ is the permittivity of vacuum. 

The force acting between two magnetic poles is called magnetic force.

Together electrostatic force and magnetic force is known as electromagnetic force.

Weak nuclear force (F_w):

It is a force that appears only between elementary particles involved in a nuclear process such as the β-decay of a nucleus.  It is a short range force that operates only over the size of a nucleus (= 10⁻¹⁵ m)

Strong nuclear force(F_s):

The strong attractive force which binds together the protons and neutrons in a nucleus is called strong nuclear force. It is a short range force that operates only over the size of a nucleus (= 10⁻¹⁵ m)

Q4. What are the different conservation laws in Physics?

Ans. Conservation laws: in any physical process involving the different forces, some physical quantities, remain unchanged with time. Such quantities are called conserved quantities. The laws which govern the conservation of these quantities are called conservation laws.

There are four basic conservation laws:

a. Law of conservation of energy.

b. Law of conservation of linear momentum

c. Law of conservation of angular momentum

d. Law of conservation of charge.

Q5. Name the scientist who was first awarded two Nobel prizes.

Ans. Madame Marie Curie , for physics ine 1903 and for chemistry in 1911.

Q6. Who first discovered radioactivity?

Ans. A H Becquerrel in 1896.

Q7. Mention some important contributions of Albert Einstein to physics.

Ans. a. Mass energy equivalence

         b. Photoelectric effect

         c. Special theory of relativity

         d. General theory of relativity.

Q8. Name the Indian physicist who was first awarded the Nobel prize.

Ans. C V Raman.

Q9. What was the important discovery of CV Raman?

Ans. Inelastic scattering of light by molecules.

Q10. What was the major contribution of Indian physicist SN Bose?

Ans. Quantum statistics ( Bose Einstein statistics)

Q11. With which field work was the famous Indian physicist H J bhabha associated?

Ans. Cascade process in cosmic radiation.

Q12. Name the Indian physicist associated with the triple helical structure of proteins.

Ans. G N Ramachandran.