Cls 9 Chp 7 Notes

       Class 9 Science Notes      

      Chapter 7 Diversity In Living Organisms   

Introduction

→ All living organism are grouped on the basis of their similarities and increasing complexities into different complexities.

→ Biodiversity means the variety of living organisms present on a particular region.

→ There are about 20 lac organisms known on the earth which differ from one another in external form, internal structure, mode of nutrition, habitat, etc.

• Taxonomy: It is a branch of biology which deals with identification, nomenclature and classification of organisms. Carolus Lannaeus is called the father of taxonomy.

Classification

→ The method of arranging organisms into groups or sets on the basis of similarities and differences is called classification.

Importance of Classification

→ It makes the study of wide variety of organisms easy and in systematic manner.

→ It helps to understand how the different organisms have evolved withtime.

→ It helps to understand the inter-relationships among different groups of organisms.

→ It forms a base for the study of other biological sciences, like biogeography.

Basis of Classification

→ There are certain features or properties used for the classification of living organisms which are known as characteristics.

→ Organisms with same characteristics are placed in same groups.

Classification System

• Two kingdom classification: Carolus Linnaeus in 1758 classified the living organisms into two groups as plants and animals.

• Five kingdom classification: H. Whittaker in 1959 further classified the organisms into five kingdoms as Kingdom Monera, Kingdom Protista, Kingdom Fungi, Kingdom Plantae and Kingdom Animalia.

→ Carl Woese in 1977 further divided Kingdom Monera into archaebacteria (or Archae) and Eubacteria (or Bacteria).

• Hierarchy of Classification: Linnaeus proposed a classification system by arranging organisms into taxonomic groups at different levels according to the characteristics they have.

Groups or Levels from top to bottom

→ The major characteristics considered for classifying all organisms into five major kingdoms.

• Type of cellular organization

(i) Prokaryotic cells: These are primitive and incomplete cells without well-defined nucleus.

(ii) Eukaryotic cells: These are advanced and complete cells with well-defined nucleus.

• Body organization

(i) Unicellular organisms: These are organisms made up of single cell with all activities performed by the single cell.

(ii) Multicellular organisms: These are organisms made up of large number of cells with different functions performed by different cells.

• Mode of obtaining food

(i) Autotrophs: These are the organisms that make their own food by photosynthesis.

(ii) Heterotrophs: These are the organisms which depend on other organisms for food.

Five Kingdom Classification

R. H. Whittaker taxonomist was the first one to propose five kingdom classification.

Monera

(i) Type: Unicellular Prokaryotic

(ii) Mode of nutrition: Autotrophic or heterotrophic

(iii) Body: Lack well-defined nucleus and cell organelles

(iv) Examples: Bacteria, Blue-green algae

Protista

(i) Type: Unicellular Eukaryotic

(ii) Mode of nutrition: Autotrophic or Heterotrophic

(iii) Body: Some organisms use pseudopodia or cilia or flagella for movement

(iv) Examples: Amoeba, Paramecium, Euglena

Fungi

(i) Type: Multicellular Non-green Eukaryotic

(ii) Mode of nutrition: Saprophytic or Parasitic Sometimes symbiotic

(iii) Body: Fungus is made up of long filaments called hyphae. The network of hyphae is mycelium.

(iv) Examples: Yeast, Rhiozpus, Mushrooms moulds

Animalia

(i) Type: Multicellular Eukaryotic

(ii) Mode of nutrition: Heterotrophic

(iii) Body: Exhibits high level of tissue differentiation and have specialized body organs. They have well developed nervous system.

(iv) Examples: Fish, Insects, Animals, Humans, Birds

Kingdom I: Monera

(i) Prokaryotic, unicellular.

(ii) Can be autotrophs or heterotrophs.(iii) May or may not have cell wall.

(iv) Examples: Anabaena and Bacteria (heterotrophic), Cyano-bacteria or Blue-green algae (autotrophic).

Kingdom II: Protista

(i) Eukaryotic, unicellular.

(ii) Can be autotrophic or heterotrophic.

(iii) May have cilia, flagella or pseudophodia for locomotion.

(iv) Examples: Plants like unicellular algae, diatoms; animals like protozoans (Amoeba, Paramecium, Euglena); fungi like slime molds and water molds.

Kingdom III: Fungi

(i) Eukaryotic.

(ii) Mostly multicellular but sometimes unicellular (yeast).

(iii) Source of food:

• Mostly saprophytes: These organisms use decaying material for food.

• Some parasitic: These organisms live inside body of other living organism to have food and can be disease causing.

• Symbiotic relation: These are relations between two organisms in which they live together for benefit of one or both.

→ Lichens are a symbiotic relation between fungi and cyanobacteria.

→ Here fungi gets food from cyanobacteria and in return cyanobacteria gets water and protection from sunlight through fungi.

(iv) Cell wall is made of chitin.

(v) Examples: Mushrooms (Agaricus), green mold (Penicillium), smut (Aspergilus).

Kingdom IV: Plantae

(i) Eukaryotic, multicellular.

(ii) Autotrophs.

(iii) Cell wall present.

Basis of division in Kingdom Plantae

(i) Differentiated body parts: Body is differentiated into leaves, stems, roots, flowers, etc.

(ii) Presence of vascular tissue: There are two types of vascular tissues present in the plants.

• Xylem: Helps in transport of water.

• Phloem: Helps in transport of food.

(iii) Reproduction through seeds or spores:

• Phanerogamae : Plants with seeds are called phanerogamae. They contains embryo with stored food and are multicellular.

• Cryotogamae: Plants with spores are called cryptogamae. They contains only naked embryo and are generally unicellular.

(iv) Seeds are inside the fruit or naked:

• Angiospermae: These are plants with seeds inside the fruit and bears flowers.

• Gymnospermae: These are plants with naked seeds and do not bear flowers.

Division 1: Thallophyta

(i) Basic and elementary plants with undifferentiated body parts.

(ii) Generally called algae.

(iii) No vascular tissue present.

(iv) Reproduce through spores.

(v) Mainly found in water.

(vi) Example: Ulva, Spirogyra, Ulothrix, Cladophora, Chara.

Division 2: Bryophyte

(i) Body structure differentiated but not fully developed.

(ii) No vascular tissues present.

(iii) Reproduce through spores.

(iv) Found on both land and water therefore known as ‘Amphibians of Plantae Kingdom’.

(v) Example : Liverwort (Marchantia, Riccia), Mosses (Funaria), Hornwort (Dendrocerous).

Cls 9 Chp 3 notes

         Class 9 Science Notes       

         Chapter 3 Atoms And Molecules      

Introduction

→ Around 500 B.C., Indian philosopher Maharishi Kanad, postulated the theory if we go on dividing matter (padarth), we will obtain smallest particle beyond which further division can't be possible which is known as 'parmanu'.

→ Ancient Greek philosophers – Democritus and Leucippus called these particles atoms.

→ Antoine L. Lavoisier laid the foundation of chemical sciences by establishing two important laws of chemical combination.

Laws of Chemical Combination

• This law established after the experiments by Lavoisier and Joseph L. Proust.

• The chemical reaction between two or more substances give rise to products which is governed by certain laws called Laws of Chemical Combination.

• Law of Conservation of Mass

→ During a chemical reaction, the total mass of reactants will be equal to the total mass of the products.

→ Mass can neither be created nor destroyed in a chemical reaction.

→ Example: A (reactant) + B (reactant)→ AB (product)

mass of A + mass of B = mass of AB

• Law of Constant Proportions

→ In a chemical reaction, compounds always contain the same elements present in definite proportions by mass irrespective of their source.

→ It was given by Lavoisier.

→ For example: (i) 18 gm of H2O = 2 gm of hydrogen + 16 gm of oxygen

⇒ mass of hydrogen/mass of oxygen = 2/16 = 1/8

(ii) 36 gm of H2O = 4 gm of hydrogen + 32 gm of oxygen

⇒ mass of hydrogen/mass of oxygen = 4/32 = 1/8(iii) 9 gm of H2O = 1 gm of hydrogen + 8 gm of oxygen

⇒ mass of hydrogen/mass of oxygen = 1/8This verifies law of constant proportions as the ratio of mass of hydrogen to oxygen is always same.

Dalton's Atomic Theory

→ According to Dalton’s atomic theory, all matter, whether an element, a compound or a mixture is composed of small particles called atoms.

→ Six Postulates of Dalton's atomic theory:

(i) All matter is made of very tiny particles called atoms.

(ii) Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction.

(iii) Atoms of a given element are identical in mass and chemical properties. (Law of conservation of mass)

(iv) Atoms of different elements have different masses and chemical properties.

(v) Atoms combine in the ratio of small whole numbers to form compounds. (Law of constant proportion)

(vi) The relative number and kinds of atoms are constant in a given compound.

Atoms

• Atoms are building blocks of all matter.

• According to modern atomic theory, an atom is the smallest particle of an element which takes part in chemical reaction.

•  Atoms are very small and which can’t be seen even through very powerful microscope.

• Atomic radius is measured in nanometres. Nanometres = 10^-9 m

• Modern day symbols of Elements

→ Dalton was the first scientist to use the symbols for elements.

→ Berzilius suggested that the symbols of elements should be made from one or two letters of the name of the element.

→ The name copper was taken from Cyprus, a place from where it was found for first time.

→ Now, IUPAC (International Union of Pure and Applied Chemistry) approves names of elements.

→ The first letter of a symbol is always written as a capital letter (uppercase) and the second letter as a small letter (lowercase). For example: hydrogen (H), aluminium (Al), cobalt (Co).

→ Some other symbols have been taken from the names of elements in Latin, German or Greek. For example: Fe from its Latin name ferrum, sodium is Na from natrium, potassium is K from kalium.

Atomic Mass

→ Dalton’s atomic theory proposed the idea of atomic mass which explained the law of constant proportions so well.

→ The mass of an atom of an element is called its atomic mass.

→ In 1961, IUPAC have accepted ‘atomic mass unit’ (u) to express atomic and molecular mass of elements and compounds.

→ The atomic mass unit is defined as the quantity of mass equal to 1/12 of mass of an atom of carbon-12.

1 amu or u = 1/12 × Mass of an atom of C^12

1 u = 1.66 × 10^-27 kg

• Atom existence

→ Atoms of most of the elements are very reactive and does not exist in free state.

→ Only the atoms of noble gases (such as He, Ne, Ar, Kr, Xe and Rn) are chemically unreactive and can exist in the free state as single atom.

→ Atoms of all other elements combine together to form molecules or ions.

Molecules

→ A molecule is in general a group of two or more atoms that are chemically bonded together

→ A molecule is the smallest particle of matter (except element) which is capable of an independent existence and show all properties of that substance.

→ Examples: ‘H2O’ is the smallest particle of water which shows all the properties of water.

→ A molecule may have atom of same or different elements, depending upon this, molecule can be categorized into two categories:

(i) Homoatomic molecules (containing atom of same element)

Examples: H2, O2, O3, S8, P4 etc.

(ii) Heteroatomic molecules or compounds (containing atoms of different elements)

Examples:  H2O, CO2, NaCl, CaCO3 etc.

Atomicity

→ The number of atoms present in one molecule of an element is called its atomicity.

Chemical Formulae

→ It is the symbolic representation of the composition of a compound.

• Characteristics of chemical formulae→ The valencies or charges on ion must balance.

→ When a compound is formed of metal and non-metal, symbol of metal comes first. E.g., CaO, NaCl, CuO.

→ When polyatomic ions are used, the ions are enclosed in brackets before writing the number to show the ratio.

E.g., Ca(OH)2 , (NH4)2SO4

Rules for writing chemical formulae

(i) We first write symbols of elements which form compound.

(ii) Below the symbol of each element, we should write their valency.

(iii) Now cross over the valencies of combining atoms.

(iv) With first atom, we write the valency of second atom (as a subscript).

(v) With second atom, we write the valency of first atom (subscript).

Molecular mass

→ It is the sum of atomic masses of all the atoms in a molecule of that substance.

Example: Molecular mass of  H2O = 2×Atomic mass of Hydrogen + 1×Atomic mass of Oxygen

So, Molecular mass of  H2O = 2×1 + 1×16 = 18 u

Formula Unit Mass

→ It is the sum of atomic mass of ions and atoms present in formula for a compound.

Example: In NaCl,

Na = 23 a.m.u.

Cl = 35.5 a.m.u.

So, Formula unit mass = 1×23 + 1×35.5 = 58.5 u

Ions

→ An ion may be defined as an atom or group of atoms having positive or negative charge.

→ Some positively charged ions : Na+ , K+, Ca2+ , Al3+→ Some negatively charged ions : Cl- (chloride ion), S2- (sulphide ion), OH- (hydroxide ion), SO42-  (sulphate ion)

• We can classify ions in two types:

(i) Simple ions

Mg2+  (Magnesium ion)

Na+  (Sodium ion)

Cl-  (Chloride ion)

Al3+  (Aluminium ion)

(ii) Compound ions

NH4+  (Ammonium ion)

CO32- (Carbonate ion)

SO42- (Sulphate ion)

OH- (Hydroxide ion)

Chemical Formulae of Ionic Compounds (Polyatomic)

Mole Concept

→ A group of 6.022×10^23 particles (atoms, molecules or ions) of a substance is called a mole of that substance.

→ 1 mole of atoms = 6.022×10^23 atoms

→ 1 mole of molecules = 6.022 × 10^23 molecules

Example, 1 mole of oxygen = 6.022×1023 oxygen atomsNote: 6.022×1023 is Avogadro Number (L).

→1 mole of atoms of an element has a mass equal to gram atomic mass ofthe element.

Molar Mass

→ The molar mass of a substance is the mass of 1 mole of that substance.

→ It is equal to the 6.022×10^23 atoms of that element/substance.

Examples:

(a) Atomic mass of hydrogen (H) is 1 u. Its molar mass is 1 g/mol.

(b) Atomic mass of nitrogen is 14 u. So, molar mass of nitrogen (N) is 14 g/mol.

c) Molar mass of S8 = Mass of S×8 = 32×8 = 256 g/mol

(d) Molar mass of HCl = Mass of H + Mass of Cl = 1 = 35.5 = 36.5

Important Formulae

Cls 6 Chp 16 Notes

          Class 6 Science Notes           

       Chapter 16 Garbage In, Garbage Out      

Introduction

→ Garbage is an undesired and unwanted material.

→ It is also referred to as rubbish, junk or trash.

→ Proper disposal of garbage is necessary for maintaining cleanliness in surroundings.

Sources of waste

(i) Domestic wastes: Vegetable peels, paper, food leftover and plastics are domestic waste.

(ii) Industrial waste: Wastes which produced from industries like plastic, glass, fly ash, smoke etc.

(iii) Commercial wastes: These wastes come from generated from commercial establishment such as hotels, malls, auto-repair shops, medical facilities.

(iv) Agricultural wastes: These wastes are rice husk, dried stems and weeds and cattle waste.

Types of waste

→According to mode of decomposition, there are three types of wastes:

(i) Biodegradable wastes

(ii) Non-biodegradable wastes

(iii) Plastics

Biodegradable wastes

→ Wastes which broken down into simple constituents by the action of microorganisms.

→ Examples: animal wastes, organic wastes, domestic refuse etc.

Non-biodegradable wastes

→ Wastes which cannot be disintegrated by action of microorganisms and remain unaffected from decomposition.

→Examples: glass, scraps, metal etc.

Plastics

→ It cannot converted into less harmful substances by composting.

→ Examples: bottles, pipes, shoes, bags etc.

Separation of garbage at landfill

Useful components

→ The part of garbage which can be re-used is known as useful component.

→This components are then re-treated with some process to make it non-toxic.

Non-useful components

→ The part of garbage which cannot be used is known as non-useful components.

→ This components are then separated and spread on the land and put sand layer on it.

Ill effect of plastics

(i) Plastic bags choke sewer system.

(ii) Burning emits poisonous gases cause health problems.

(iii) Food stored in bad quality plastic may harmful for body

(iv) Food eaten by animals from plastic bags which may lead to death.

Management of plastics

(i) Do not burn plastic bags or other plastic items

(ii) Do not throw plastic here and there after use

(iii) Use paper bags or cloth bags instead of plastic bags

(iv) Educate family members and friends about the proper disposal of plastics.

vermicomposting

→ It is a method of preparing compost with the help of red worms is known as vermicomposting.

→ Excreta of the worms make the compost very rich in nutrients.

→ Vericompost is organic fertilizer, nutrient-rich and soil conditioner.

How to reduce garbage?

Reduce

→ We have to reduce our consumption.

→ We should use an item when it is necessary to use.

Reuse

→ We can reuse substances many items.

→ For example: newspaper into book cover or as a bag.

Recycle

→ It is a process in which used materials converts into new products in order to prevent the waste of potentially useful materials.

Cls 6 Chp 15 Notes

            Class 6 Science Notes          

             Chapter 15 Air Around Us            

 What is air?

→ Air is a mixture of gases and dust particles. It is a clear gas in which living things breathe and live.

→ Air is a matter it has volume and mass. It creates atmospheric pressure.

→ In vacuum there in no air present over there.

Atmosphere: It is a thick layer of air surrounding the earth’s surface is known as atmosphere.

Wind: The moving air is known as wind.

Air composition

→ Air contains mainly oxygen, nitrogen and remaining includes noble gases, carbon dioxide, water vapour, traces of other gases and dust particles.

→ Oxygen and nitrogen: air contains 28% oxygen and 78% nitrogen.

→ Oxygen helps in burning. It is used by living things to respire,

→ Nitrogen helps in growth of plant.

Carbon dioxide

→ Air contains 0.003% of carbon dioxide.

→ Carbon dioxide is also produced during burning.

→ Plants and animals produce carbon dioxide during respiration

Water vapour

→ Air contains some amounts of water vapour depends upon the weather of a place.

→ Water vapour presence is very important for water cycle in nature.

Dust and Smoke

→ Smoke contains few gases with fine dust particles and is often harmful.

How does oxygen become available for all living beings?

Plants

→ They use carbon dioxide of the air to make their own food by a process called photosynthesis.

Aquatic animals

→ Most aquatic animals have special organs for respiration called gills. They use oxygen from air dissolved in water.

Amphibians

→ Some amphibians like frogs, salamanders need breathing systems for both water and air.

→ Frogs have lungs to breathe air when on land. In water, frogs breathe with their moist skin.

Birds

→ They have pair of lungs with air sacs which is open all the time, because birds need high level of oxygen during flight.

Mammals

→ They breathe with the help of lungs. They take oxygen and give out carbon dioxide.

Properties of oxygen

→ Air is colourless

→ Air is transparent

→ It is essential for life

→ It occupies space

→ It present everywhere including water and soil

→ It exerts pressure

Cls 6 Chp 14 Notes

           Class 6 Science Notes       

            Chapter 14 Water              

Water and Forms of water

→ Water is a natural resource which is vital for both plants and animals. It is made up of tiny molecules oxygen and hydrogen.

→ Earth surface is covered with water is about three-fourth in ratio. That is why earth is known as water planet.

Forms of water

(i) Solid: ice which is found at the poles of the earth. The glaciers and snow covered mountains is solid form of water.

(ii) Liquid: rivers, lakes, seas and oceans are liquid form of water.

(iii) Gas: water vapour is present all around us.

Uses of water

→ Farmers need lot of water to irrigate the crop, factories need lot of water to produce the items required, water use in our daily life activity like bathing, drinking, washing and cooking etc.

Sources of water

Rain water

→ It is a prime source of water.

→ Physically rain water is clear, sparkling and bright.

→ Bacteriologically rain water is free from pathogenic agents.

→ Chemically it is very soft containing traces of dissolved solids.

Surface water

→ It is originate from rain water. It is main source of water supply in many areas.

→ It is prone to contamination from animal and human sources.

→ It needs to purify before use.

→ Example: lakes, river, tanks etc.

Ground water

→ It is the cheapest and most practical means of providing water to small communities.

→ It is superior to surface water because the ground itself provides an effective filtering medium.

Water cycle

→ It is a continuous circulation of water in nature is called water cycle.

• It consists in three processes:

(i) Evaporation: it is a conversation of liquid into vapour is called evaporation.

(ii) Precipitation: it is falling down of water from clouds is called precipitation.

(iii) Runoff: it is a process in which the water of the land usually reaching the sea.

Rain water harvesting

→ It is a way to increase the availability of water to collect rainwater and store it for later use.

→ Collection of rain water in this way is called rain water harvesting.

→ Rooftop rain water harvesting: the rain water is collect from the rooftop to a storage tank, through pipes.

→ Other option is to allow water to go directly to the ground from the roadside drains that collect rainwater.

Scarcity of water

→ It is a situation where there is insufficient water to satisfy normal requirements.

• The factors of scarcity of water are:

→ Increasing industries

→ Agricultural activities

→ Increasing population

→ Deforestation

Cls 6 Chp 13 notes

           Class 6 Science Notes        

       Chapter 13 Fun With Magnets     

What is Magnet?

→ A material or objects that have property of attraction or pull force for ferromagnetic materials like iron, cobalt, nickel etc. is called magnets.

→ Magnets attract Ferromagnetic materials like Iron towards it.

→ Magnets also attract and repel other magnets.

→ Applications of attraction property of magnets in day to day life are – Refrigerator doors, pencil boxes or purses with magnetic closure buttons, iron separator from waste etc.

Types of Magnets

(i) Natural magnets: Those magnets which found naturally and have low magnetic power is called natural magnets.

Example: magnetite, lodestone.

(ii) Artificial magnets: Magnets which is made by humans and have a strong magnetic power with different shapes.Example: iron, nickel and cobalt

Magnetic and non-magnetic material

(i) Magnetic material

→ Materials which are attracted towards a magnet are called magnetic materials.

→ Example: iron, nickel

(ii) Non-magnetic materials

→ Materials which do not attracted towards a magnet are called non-magnetic materials.

→ Example: zinc, wood etc.

What is magnetism?

→ It is a property of magnet in which magnet is attract things made up of Iron, Cobalt or Nickel is known as magnetism.

What is magnetic field?

→ The area of magnet in which magnetic force is exerted to attract iron is known as magnetic field.

Magnetic poles

→ It is end part of the magnet where the magnetic force is concentrated are called magnetic poles.

→ Magnet has 2 poles.

(i) North Pole: When one pole of the magnet always points towards north. This is known as north-pole.

(ii) South Pole: When one pole of the magnet always points towards south. This is known as south-pole.

Properties of magnet

→ Magnet attract magnetic materials

→ Same poles repel each other, different poles attract each other

→ The freely suspended magnet always rests in N-S direction.

Uses of magnet

→ It is used in a compass to find the direction.

→ It is used for lifting heavy masses of iron

→ Used by surgeons to remove steel splinters from the wounds

→ It is used in electric bells and telephones etc.

Finding directions using Magnet

→ A freely suspended magnet always comes to rest in North-South direction. In olden days this property has been used to find directions.

→ Compass is used to find directions.

Attraction and Repulsion

• Magnets attract iron but can attract and repel another magnet.

→ Like or same poles of two magnets when brought closer, they repel each other.

→ Example: South Pole of one magnet repels South Pole of other.

• Unlike or different poles of two magnets when brought closer, they attract each other.

→ Example: South Pole of one magnet attracts North Pole of other.

Cls 6 Chp 12 Notes

          Class 6 Science Notes           

         Chapter 12 Electricity and Circuit      

Electricity 

→ It is a set of physical phenomena which involves an electrical charge.

What causes an electrical charge?

It is caused by an imbalance in positive or negative charge.

Source of electrical energy

→ Electrical energy is available to us from electric power houses, domestic generators, dry cells and batteries.

Electric current

→ It is a flow of electric charges, these electric current flows in one direction only.

→ Examples: oven, room heater, ceiling fan and electric bulb work when an electric current flows through them.

Source of electric current

→ It is a device which is used to produce an electric current is called a source of electric current.

→ Common sources of electric current are cells and batteries which comes in various shapes and sizes and electric current that we get from plug points in houses.

Flow of electric current

→ Cell, battery or a plug point acting as a source.

→ Copper, silver or aluminium wires allow electric current flow easily.

→ An unbroken loop (of the wire) running from one terminal of the source, through various appliances, back to the other terminal of the source.

Electric circuit

→ It provides a path through which electricity travels from one terminal of the cell through the bulb and back to the other terminal of the cell is called electric circuit.

Examples

→ Some electric circuits in the natural world

• Nerves in our body create electric circuit

• Lightning, clouds and planet earth form an electric circuit

→ Some man- made electric circuits are:

• Wiring that lights our house

• Car battery, ignition switch and starter in a car.

Type of circuits

(i) Closed circuits

→ It is unbroken path travelled by electricity is known as a closed circuit it is also known as complete circuit.

→ If the circuit is complete or closed, the bulb lights up.

→ The direction of flow of electricity is from the positive terminal of the cell to the negative terminal of the cell.

(ii) Open circuits

→ It is broken path by which electricity cannot pass is known as open circuit also known as incomplete body.

→ A bulb will not light up if there is a gap in circuit. If the circuit is open the bulb will not light up.

Component of electricity

(i) Connecting wires: It helps to conduct the electric current and complete the circuit.

(ii) Bulb: when circuit is complete the lights up.

(iii) Battery: it is a series combination of two or more cells.

(iv) Switch: a switch works by breaking or completing the circuit path.

→ Switch on: The circuit path is complete.

→ Switch off: the circuit path is broken.

(v) Electric cell or dry cell

→ An electric cell has two terminals; one is called positive while the other is negative.

→ Inside the electric cell, the electric charges flows from negative terminal to the positive terminal.

→ Connecting wires, bulb, switch and electric cell is used in torch, battery, LED etc.

Conductor and insulator

(i) Conductor:

→ Materials which allow electric current passes through it, is known as conductor.

→ All metals are good conductor, only non-metal which is good conductor for electricity is carbon.

→ A few non-metals like graphite (pencil lead is made of graphite) are also conductors of electricity.

Cls 6 Chp 11 Notes

           Class 6 Science Notes         

     Chapter 11 Light, Shadows and Reflections      

Light 

→ It is a form of energy which is responsible for seeing objects.

→ When light falls on an object, some light get reflected, this reflected light come to our eyes and we are able to see an object.

→ Example: sun, torch, candle, fireflies and glow worm etc.

Sources of light

(i) Luminous object: The objects which emit their own light is called luminous object.

→ Example: sun, torch bulb, star

(ii) Non-luminous object: The objects which do not emit their own light is called non-luminous object.

→ Example: Moon, shoe, trees.

Types of materials transmit light

→ There are three types of materials which transmit light:

(i) Transparent

(ii) Translucent

(iii) Opaque

(i) Transparent

→ These objects allow light to pass through them in straight line completely.

→  We can see through these objects clearly.

→  Examples: air, water, etc.

(ii) Translucent

→ These objects allow light to pass through them partially.

→ The object is not clearly seen in translucent object.

→ Examples: Tissue paper, frosted glass, butter paper, etc.

(iii) Opaque

→ These objects do not allow light to pass through them.

→ We can’t see the object through this.

→ Examples: wall, door, trees etc.

Characteristics of light

→ Light travels in straight line

→ Light can be reflected

→ Light can be bent

→ The speed of light is 3 × 108 m/sec

→ Light can be polarized

Shadow

→ When an opaque object blocked the path of light it forms a dark portion on the opposite side of the object this dark portion is known as shadow.

Properties of shadow

→ The object must be opaque or translucent

→ Transparent object do not make shadow

→ It is dark in color

→ It is formed opposite to the source of light

→ It gives the information about the shape of object

→ Size of shadow can be increase or decrees by change in distance between object and screen are changed.

Pin hole camera

→ It is a toy device use to study light travels in straight lineProperties of image formed by a Pin Hole Camera

(i) Image formed by a pin hole camera is coloured.

(ii) Image formed by a pin hole camera is inverted.

(iii) Image formed by a pin hole camera is smaller in size.

Rectilinear propagation of light

→ Light travels in a straight line are called rectilinear propagation of light.

Important terms regard rectilinear propagation of light

(i) Ray of light: It is a path along which light travels in the given direction.

(ii) Beam of light: Bunch of ray of light travel in the given direction.

Mirror

→ A mirror is a polished surface which can make the image of an object.

Types of Mirror

(i) Plane mirror: Image formed is of the same size

(ii) Concave mirror: Reflecting surface is bent–in.

(iii) Convex Mirror: Reflecting surface is bulged-out.

Reflection

→ When light falls on a mirror, light wave may change their direction upon the striking surface this phenomena is called reflection.