Class 6 keywords

Subject: Class 6 keywords

Chap 1

Ingredients :-components used to prepare food are called ingredients.

Edible:- Eatable parts of plants is called edible . For example:- leaf, root, fruit etc.

Nectar:- sweet juice from flowers that need collect and convert it into honey and store in their hive is called nectar.

Sprouted seeds:- Sprouts is the white root like structure coming out of seeds when soaked in water overnight. Seeds with sprouts are called sprouted seeds.

Herbivore :- Animals which eat only plants.

Carnivore:- Animals which eat only animals

Omnivore:- Animals which eat both plants as well as animals.

 Chap 2

1. Balanced diet:- Food which contains carbohydrates, fats, proteins, vitamins , minerals and water in proper proportion is called balance diet.

2. Beriberi:- Disease which is caused due to deficiency of vitamin B

3. Carbohydrates:  the main component of food that provides us energy in the form of glucose.

4. Energy:-  capacity to do work

5. Fats:- Component of food that provide energy to our body more than carbohydrate.

6. Minerals:- Nutrient needed for growth and maintenance

Or

Component of food that are necessary for building proper growth and maintenance of our body.

7. Nutrients:- Components of food such as carbohydrates, fats, proteins, vitamins , minerals and water are called nutrients.

8. Proteins:-Body building nutrient

Or

 Component of food that our body use to build and repair tissues  is called proteins.

9. Roughage:- Dietary fibres which do not provide any nutrient to our body but helps our body get rid of undigested food.

10. Scurvy:- Disease which is caused by deficiency of vitamin C.

11. Starch:- Stored food of plants is called starch.

12. Vitamins:- Nutrient protect body from disease. 

Or

Components of food that are needed for growth and development. It also provides immunity  our body

Chap 3

Cotton wool :- The mass of cotton obtained by spinning is called cotton wool.

Fabric :- The substances that are made from yarns and then turn into fibres is called fibres.

Fibre:- When you untwist a yarn to loosen it, we see that it is made up of multiple thin hair-like strands called Fibres.

Knitting:-The process of getting a single yarn together to form a fabric is called Knitting.

Spinning:- The process of making yarn from fibres is called Spinning.

Weaving:- The process of Arranging two sets of yarns together to make a fabric is called weaving

Yarn :- A fabric is made up of fine threads called yarns

Chap 4

Hard :-Materials which are difficult to compress, cut or break are referred to as Hard. Eg: Iron, Copper.

Insoluble:- Insoluble substances are those which don't disappear or dissolve when mixed with water. Eg: sand, chalk, sawdust

Lustre :- Lustrous materials are those materials that have shiny surfaces. It include metals like silver, gold, iron and aluminium

Material :- Material refers to the matter from which the thing is made. Eg: A water bottle is made of plastic, a mirror is made of glass, a table is made of wood etc

Metals :- substances which appear bright and shiny are called metals

Opaque :- Materials which don't allow light to pass through them completely are called Opaque objects. Objects on the other side of opaque objects cannot be seen at all. Eg: Wood, metals etc.

Rough :- Material which have irregularities on its surface is called Rough .

Soluble :- Soluble substances are those which disappear when mixed with water. Eg: salt, sugar

Translucent :- Materials which allow light to pass through them partially are called Translucent objects. Objects on the other side of translucent objects can be seen but not very clearly.Eg: Oily paper, certain types of designed glass, tissue paper etc

Transparent:- Materials which allow light to pass through them completely are called Transparent objects. Objects on the other side of Transparent objects can be seen clearly. Eg: Glass, water and air.

Chap 5 Separation of substances

1. Churning:-It is the process of separation of the lighter particles of a suspended solid from a liquid. For example, to obtain butter from the curd or milk.

2. Condensation:- The process of conversation of water vapour into its liquid form is called condensation.

3. Decantation:-process of removal of water (or any other solute) along with lighter dust particles is called Decantation.

4. Evaporation:-process of conversion of a liquid into its vapor is called Evaporation

5. Filtration:-process of separating solid particles from a liquid by passing through a filter or pores of filter paper is called filtration.

6. Hand picking:- Manually separating stones, dust, husk from grain, rice and wheat is referred to as handpicking.

7. Saturated solution:- Solution in which no more solute can be disolve in a given solvent is called saturated solution.

8. Sedimentation:- process of separation of heavier components by adding water  such that the heavier particles settles down is called Sedimentation.

9. Sieving:-The process of separating fine particles from the larger particles by using a sieve, is called sieving.

10. Solution:- homogeneous mixture of solute and solvent is called solution.

11. Threshing:- Stalks of grains are dried in the Sun.Once they are dry, they are manually beaten hard to free the grains from the stalks. This is referred to Threshing

12. Winnowing:-  Process by which  heaver and lighter components of a mixture is separated by wind or by blowing air is called winnowing.

 Chap 6 Changes around us

Changes:- The difference that become In our surroundings after some time is called change

Contraction:-  A process in which an object becomes smaller or shrinks is called contraction

Evaporation:- process of conversion of a liquid into its vapor is called Evaporation

Expansion:- A process in which an object becomes bigger in size, e.g., metals expand on heating.

Melting:-A process in which a solid melts to become a liquid on heating is called melting.

Chap 7 Getting to know plants

Keywords 

1. Climber :- Some plants take support on the neighboring structures, like wall, tree, fence and climb up are called climbers.

For example: Money plant, Pea plant, Grapevine, Bean plant etc.

2. Conduct :- The passage through which water and food move is called conduct.

3. Creepers :-Some plants with weak stem needs support, they cannot stand upright by their own and spreads on the ground are called creepers.

For examples: Pumpkin, Watermelon, Sweet potato, Muskmelon etc.

4. Fibrous roots :- Roots in which no main root occur . Example :- grasses.

5. Herbs:-Plants with green and tender stems are called herbs For example: mint (Pudhina), rosemary, coriander (Dhaniya), bay leaf (Tejpatta), basil (Tulsi).

6. Lamina:-The broad green part of leaf is called lamina

7. Lateral roots:- Small roots arises from tap root is called lateral roots.

8. Midrib:-A thick vein in the middle of the leaf is called midrib.

9. Ovule:- Some small bead like structures inside the ovary is called ovules.

10. Parallel Venation:-If the design made by veins is parallel to one another in a leaf is called parallel venation. For example: grass, wheat, maize etc

11. Petal:-The colored part of flower that covers the reproductive part of flower

12. Petiole:-The part of leaf by which it is attached to the stem is called petiole

13. Photosynthesis:- The Process by which plants prepare food in the presence of Carbon dioxide, water , sunlight and chlorophyll is called photosynthesis.

14. Pistil:-The innermost part which contains stigma , style and ovary.

15. Reticulate venation:-If the design is net like on both sides of midrib is called reticulate venation. For example: coriander, rose, oak etc.

16. Sepal:-The outermost green color part that enclose the bud.

17. Shrubs:-Some plants have stem branching out near the base there stem is hard but not too thick these are called shrubs

Example :- Hibiscus

18. Stamen:-The pollen producing part of flower. It has two parts, first is anther which contains pollen grains and second is filament, the tube like structure supporting anther.

19. Taproot:-The main root which is larger and fast growing is called tap root and the branched smaller roots is called lateral root.

For example: Beet root, Carrot, Sugar beet, Radish, etc.

20. Transpiration:-Water vapors are released into the atmosphere through stomata present on leaf this process is called transpiration.

21. Trees:-Some plants are very tall and have hard and thick brown stem. The stem has branches in the upper part, much above the ground. Such plants are called trees.

For Example: Apple tree, Mango tree, Neem tree, Coconut tree, Oak tree etc

22. Veins:-Small lines present on a leaf are called its vein. These gives support and transport water and mineral through the leaf.

Chap 8 Body Movement

Keywords

1. Backbone:- If you breath in deeply you can feel with your hands the chest bone in front side which is joined to the number of small bones on the back side these small bones combinely called as backbone.

2.Ball and socket joint:- This is the type of joint in which ball shape surface of one bone fitted into the hollow space of another bone also called socket.

In this type of joint movement can be done in all the directions. For example: shoulder joint, hip joint

3.Bristles:-Short stiff hair that forms a part of brush is called bristles.

4.Cartilage:- It is softer and more flexible tissue that is  found between the joints of knee and hips.

5.Cavity:- Empty space inside something solid such as bone is called cavity.

6.Fixed joint:- these type of joints are called fixed because it does not move in any direction.

For examples : Bones present in your head also called skull bone which does not move.

7.Gait of animals:- Motion of animals is called Gait of animals.

8.Hinge joint:- Hinge joints are found between the two or more than two bones where we need back and forth movement. For example: knees, elbow, ankle joints.

9.Muscle :- Tissue that are attached to the bones and is resposible for the movement of human body. There is change in the length of muscle due to contraction and relaxation

10.Outer skeleton:- The bones present in our body form a framework and protect an animal body this frame work is called Outer Skeleton.

11.Pelvic bones :- The bones present in waist / hip joint are called Pelvic bones.

12.Pivotal joint:- Pivotal joints allow for rotation, twisting, extension, and flexibility.

This is the joint where our neck joints head and allow the movement of forward, backward, left and right direction.

13.Rib cage:- Bones which join the chest and the backbone is called ribs present left and right side of chest bone these were 12 pairs of ribs  these bones combinely called as rib cage

14.Shoulder bones :- Bones on the back are prominent .It is made up of three bones: Scapula (shoulder blade) Clavicle (collar bone) Humerus (arm bone)

15.Skeleton:- The bones present in our body form a framework this frame work is called Skeleton

16.Streamlined:- Body of fish is slimmer in the middle portion, it has tapered ends and this shape is called streamlined body.

Chapter 9

The living organisms- Characteristics and Habitats

Keywords:-

1. Adaptation:- The presence of specific features or certain habits which enables an organism to Lev naturally in a place is called adaptation

2. Aquatic habitat:- The habitat of plants and animals that live in water are called aquatic habitats. Ex :- lakes, rivers and ocean

3. Biotic component:- The Organisms, both plants and animals, living in a habitat are called biotic components

4. Excretion:- the process of getting rid of wastes by organisms is known as excretion

5. Growth:- The increases in cell size and number that take place during the life history of an organism

6. Habitat:-The place where organisms live us called habitat.

7. Living:- something that can grow, move, reproduce, respire and carry out various cellular activities is called living

8. Reproduction:-The process by which Living things produce more of their own kind is called reproduction

9. Respiration:- The process of breathe in oxygen and using by the body to obtain energy and releasing carbon di oxide produced in this process is called respiration.

10. Stimulus:- Changes in our surroundings that makes us respond to them are called stimulus

Chapter 10

Motion and measurement of distances:-

1. Circular motion:- motion where objects move along a circular path. Examples hands of a clock, blades of a fan, rotation of earth around the sun etc

2. Distance:- Distance gives the information as to how far two things are.

or

the amount of space between two places or things

3. Measurement:- Measurement is comparison on an unknown quantity with a known quantity.

4. Motion:-Objects which are moving around us are said to be in motion

5. Periodic motion:- type of motion where the object repeats its motion after a fixed interval of time. Examples pendulum of a clock, motion of child on a swing etc.

6. Rectilinear motion:- motion where objects move along a straight line. Examples march past of soldiers, sprinters in race, falling stones etc.

7. SI unit:- Scientists all over the world have accepted a set of standard units for measurements. This system of units is called International System of Units (SI units

8. Units of measurement:- Measurement is comparison on an unknown quantity with a known quantity. The known quantity is called Unit of measurement.

Chap 11

Luminous :- Objects that emit light are called Luminous Objectslike sun, bulb, tubelight

Mirror :-Mirror is an object which reflects light.

Opaque :-Materials which don't allow light to pass through them completely are called Opaque objects. Objects on the other side of opaque objects cannot be seen at all. Eg: Wood, metals etc.

Pinhole camera:-A pinhole camera is a simple camera, without lens, in the shape of a box. One of the sides has a small hole and it produces an inverted image of the outside world at other side.

Reflection:- Bouncing back of light into the same medium after striking a polished surface is called reflection of light .

Shadow:-A shadow is a space where light from a light source is blocked by an opaque object.

Translucent:-Materials which allow light to pass through them partially are called Translucent objects. Objects on the other side of translucent objects can be seen but not very clearly.Eg: Oily paper, certain types of designed glass, tissue paper etc

Transparent :- Materials which allow light to pass through them completely are called Transparent objects. Objects on the other side of Transparent objects can be seen clearly. Eg: Glass, water and air.

Chap 12 Electricity and Circuits

1. Bulb :-An electric bulb is a device which produces light when electricity is passed through its terminals.

2. Conductors:- Materials which allow electric current to pass through them are called conductors of electricity. Examples are iron nail, key, safety pin, water, human bodyetc.

3. Electric cell:-An electric cell is a device which produces electricity. 

It has two terminals – positive (+) and negative (-).

4. Electric circuit:- A continuous and closed path of an electric current is called electric circuit.

5. Filament:-The bulb has two thick contact wires in the center with a thin wire attached between them. This thin wire is called filament.

6. Insulators:-Materials which do not allow electric current to pass through them are called insulators of electricity. Examples are rubber, plastic, glass, air, cloth etc

7. Switch:-Electric Switch is an electrical device which can make or break an electric circuit.

8. Terminal:- End points of the cell is called terminal of the cell.

Chapter 13

Fun with Magnets:-

1. Compass:- Compass is a device used to find directions. It consists of a magnetized needle and a dial, marked with directions, inside a box with glass cover.

2. Magnet:- A Magnet is a material or objects that has a property of attraction or pull force for ferromagnetic materials like iron, cobalt, nickel etc.

3. Magnetite:- It is an ore of iron which has magnetic properties.

4. North pole:- In a freely suspended magnet, the end of the magnet that points towards North is called its North seeking end or North Pole.

5. South pole:- Pole.The end of the magnet that points towards South is called its South seeking end or South Pole.

Chapter 14 "Water"

Keywords:-

1. Clouds:- A cloud is a mass of water drops or ice crystals suspended in the atmosphere.

2. Condensation:- The process of conversion of vapour into liquid form of water is called condensation.

3. Drought:- Droughts are the conditions which involve abnormally long period of insufficient or no rainfall

4. Evaporation:- The phenomenon of change of liquid into gas at any temperature below its boiling point is called evaporation.

5. Flood:- The condition during which rain water being everywhere, even submerging the land is called as flood.

6. Ground water:- The water found below the water table is called ground water.

7. Hail:- Hail is a form of precipitation that falls as ice pellets during a severe thunderstorm.

8. Ocean:- An ocean is a continuous body of salt water that is contained in an enormous basin on Earth's surface

9. Rainwater harvesting:- Collecting rainwater and store it for later use is called rainwater harvesting.

10. Snow :- Precipitation that falls to earth in the form of ice crystals that have complex branched hexagonal patterns.

11. Water vapour:- Gaseous form of water that forms by evaporation , is called water vapour

12. Water cycle :- Continuous cycling of water among the three forms (solid, liquid and gas) keep the total amount of water on the Earth constant, this is water cycle

Chapter 15 "Air around us"

1. Atmosphere:- Our earth is surrounded by air in the form of a thin layer. This thin layer is called the atmosphere.

Or

The envelope of air that surrounds the earth is known as the atmosphere

2. Carbon dioxide:- colourless, odourless gas that is used by green plants for photosynthesis.

3. Composition of air:- Air is a mixture of nitrogen, oxygen, carbon dioxide, water vapour and a few other gases.

4. Oxygen:- The component of air that supports burning is called oxygen.  Percentage of oxygen in the air is around 20.95%

5. Nitrogen:-  it is the major part of the air that takes up four-fifth of the space (be around 78.11%) that air fills.

6. Smoke :- dark-coloured gases caused by burning of anything.

7. Windmill:- Windmill is a huge apparatus which is rotated by wind. It is used to draw water from tube wells and to run flour mills.

Chapter 16 "Garbage in , Garbage out"

Keywords:-

1. Waste:- the product, which is no longer of any use is called waste

2. Garbage:-Waste which we collect in dustbins is called garbage. It can be Domestic Waste, Industrial Waste, Community Waste, Agricultural Waste and Electronic Waste

3. Landfill:- Non biodegradable waste is separated from this garbage and thrown in low lying open area called Landfills

4. Compost:-Manure which is made by biodegradable waste is called compost.

5.Vermicomposting:- Vermicomposting is a process where decomposition of biodegradable waste is done by using earthworms.

6. Recycling:-

Recycling is the process of converting waste materials into new materials and objects.

Human eye the colourful world

 The Human eye and the colourful world

Introduction:-

Human eye uses light and enables us to see objects around us.

The human eye:-

• Human eye is the most valuable and sensitivity sense organ.
• It enable us to see beautiful, colourful world around us.
• Located in eye sockets in skull.
• Diameter of eye ball is 2.3cm

Parts of Human Eye:-

1.Cornea:- 

• Outermost, transparent, thin membrane of eye ball.
• It forms the transparent bulge on front surface of eyeball.
• Provide most of the refraction of light.
• Light enters into eye through cornea.

2.Lens:-

•  It is composed of a fabrous, jelly like material.
• Flexible
• Provides focused real and inverted image of object on the retina.
• This is a convex lens that converges light at retina.
• Also called crystalline lens.
• Flexibility provides finer adjustment of focal length required to focus object at distance on retina.

3.Iris:- 

• Dark muscular diaphragm that control the size of pupil.
• Provide colour to eye.

4.Pupil:- 

• It is the window of the eye.
• Central aperture In iris.
• Regulates and control the amount of light entering the eye.

5.Retina:-

• Delicate membrane having enormous number of light sensitive cells.
• Lens  image on the retina.
• This image is real and inverted.
• When light sensitive cells get activated upon illumination, it generate electric signal.

6.Optic nerve:-

• Electric signals generated by light sensitive cells are now sent to brain via optic nerves.
• Brain interprets these signals and processes the information so that we perceive objects as they are.
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Types of light sensitive cells:- two types

• Rod cells--> Sensitive to  dim.light
• Cone cells->Sensitive to bright light.

7. Ciliary muscles:- 

• Curvature of lens can be modified by ciliary muscles
• The change in curvature of eye lens will change its focal length.
• When the muscles relax, lens become thin and its focal length increases.
• When the muscles contract , lend become thick and it's focal decrease.

8.Spots on Retina:-

• Yellow spot --> Maximum number of Rods and Cones Cells.
• Blind spot/Black spot--> no rod and cone cells so no image formed.

9.Aqueous Humour:-

•  Fluid present between lens and cornea.

10. Vitrous humour:- 

• Fluid present between lens and Retina.

Note:- Damage or malfunctioning of any part of visual system can lead to significant loss of visual functioning 

Power of accommodation:- 

• The ability of the eye lens to adjust its focal length is called accommodation.
• Least distance of distinct vision:-
• Also called near point of eye.
• Minimum distance at which object can be seen most distinctly without strain.
• It is 25cm for normal eye.

Far point of eye:-

• The farthest point upto which eye can see objects clearly is called far point of eye 
• It is infinite for a normal eye 
• Range of human vision is 25cm to infinity.

Cataract:-

•  Crystalline lens of old age people become milky and cloudy. This condition is called cataract.
• It cause partial or complete loss of vision.
• It is possible to restore vision through a cataract surgery.

Defects of vision and their correction:-

• Sometimes, the eye may gradually lose its power of accommodation.
• The vision becomes blurred due to the refractive defects of eye 
• Common refractive defects of vision are :- 
• 1. Myopia or nearsightedness.
• 2.Hypeemetropia or Fae sightedness.
• Presbyopia
• Defects can be corrected by spherical lenses.

Myopia/Near sightedness:- 

• A myopic person can see nearby objects clearly but cannot see distant object clearly.
• Image is formed in front of retina.

Cause of Myopia:-

• Excessive curvature of eye lens.
• Elongation of eye ball

Correction of myopia:-

It is done by concave lens of approximate power.

In a myopic eye, image of distant object is formed in front of retina and not on retina.

The far point (F)of  a myopic eye is less than infinity.

Correction of myopia:- The concave lens placed in front of eye forms a virtual image of distant object at far point (F) of myopic eye.

Hypermetropia (Far sightedness)

Affected person can see far objects clearly but cannot see nearby objects clearly.

The near point of eye moves away.

Image is formed behind the retina.

Cause of hypermetropia:-

Focal length of the lens becomes too long.

Eye ball become too small.

Correction of hypermetropia:-

Use of convex lens of suitable power can correct the defect.

Presbyopia (Old age hypermetropia):-

• It is the defect of vision due to which an old person cannot see the nearby objects clearly due to loss of power of accomodation of eye.
• The near point of old person having presbyopia gradually recedes and becomes much more than 25 cm away.

Causes of presbyopia:

•  gradually weakening of ciliary muscle
• Diminishing flexibility of eye lens.
• Correction of presbyopia:-
• Use of convex lens of suitable power.

Note:- Sometimes a person may suffer from both myopia and hypermetropia.

Such people require bifocal lens for correction.

Advantage of eyes in front of face:-

Gives a wider field of view

Enhances ability to detect faint objects

It provides 3-D view.

Who can donate eye?

• Eye donors can belongs to any age group or sex .
• People who use spectacles, or those operated for cataract, can still donate the EU's.
• People who are diabetic, have hypertension, asthma and those without communicable diseases can also donate eyes.
• Eyes must be removed within 4-6 hours after death.
• Eye removal takes only 10-15 minutes. It is a simple process and does not lead to any  disfigurement.

Who cannot donate eyes?

• Persons who were infected with or dies because of AIDS , hepatitis B and C, Rabies, acute leukaemia, tetanus, cholera, meningitis or encephalitis cannot donate eyes.

Note:- one pair of eyes gives vision to two corneal blind people.

Refraction through a prism:-

Prism:- It is a pyramidal piece of glass with teo triangular and three rectangular lateral surfaces.

Angle of prism:- The angle between two adjoining lateral surfaces.Refraction through a glass slab

Angle of deviation (d) :- It is the anfla between incident ray and emergeny ray.

Dispersion of white light by a glass prism:- 

• Splitting of white light into its constituent colours is called dispersion of light.
• When white light passes through prism ,it forms a band of seven colours.
• Sequence of colours are violet, indigo, blue , green, yellow, orange and red.
• Acronym :- VIBGYOR is used to remember series of its colours.
• This band of seven colours is called spectrum.
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Why do we get these colours?

• Different colours of light bend through different angles w.r.t. incident ray as they pass through a prism.
• Red light bend least whereas violet light bend most.
• This rays of each colour emerge along different paths and thus become distinct.
• Issac Newton was the first to use a glass prism to obtain spectrum of sunlight .
• When he allowed all the colours of spectrum to pass through second prism. He again get a white light emerging outside of second prism.
• This observation gave Newton the idea that sunlight is made up of seven colours.
• Any light that give spectrum similar to that of sunlight is referred to white light.

Total internal reflection:-

• For denser to rarer medium:- angle of refraction > Angle of incidence
• The angle of Incidence for which angle of refraction is 90° is known as critical angle
• When angle of incidence is less than critical angle, then refraction occur whereas
• When angle of incidence is greater than critical angla, then light comes back in same medium. So reflection occur and then angle of incidence= angle of reflection
• When light travels from denser to rarer medium and it's angle of incidence is larger than a critical value then it  reflect back in same medium. This phenomenon is called total internal reflection.
• Note:- for total internal reflection, light must travel from  denser to rarer medium.
• Angle of incidence > critical angle.
• Since there is no mirror, so no energy is absorbed and all the light energy get reflected , so it is called total internal reflection.

Rainbow formation;-

• It is a natural spectrum appearing in the sky after rain shower.
• Rainbow is observed in the direction opposite to the Sun.
• Three phenomenon which are involved in rainbow formation are:-
• 1. Dispersion
• 2. Refraction
• 3. Internal reflection
• Some water droplets remain suspended in air after rain. These droplets behave as glass prism.
• When light enters the rain drop , it first reflect and disperses.
• Then it reflects internally and again refracts as it come out of the drop and seven colours reach the eye of the observer in the form of rainbow 
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Atmospheric Refraction:-

• Hot air is less denser (lighter) than the cooler air (heavier)
• Twinkling if stars:-
• Twinkling of  the star is due to atmospheric Refraction of the star light.
• The starlight , on entering the earth's atmosphere, undergoes refraction continuously before it reaches the earth.
• Since the atmosphere bends starlight towards the normal, the apparent position of the star is slightly different from its actual position.
• So the star appears slightly higher (above) than the actual position when it viewed  Near the horizon.
• Since the physical conditions of the earth's atmosphere is not stationary, but keeps on changing slightly . So the apparent position of the star is not stationary.
• The stars are very distinct, they are point sized source of light  so the path of rays of light coming from the Sun goes on varying slightly, the apparent position of the star fluctuate and so amount of light entering the eye flicker. So the stars appear Sometimes brighter and sometimes faint.
• This causes twinkling effect.
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Why do planets not twinkle?

• Planets are much closer to the earth and considered as a collection of point sized source of light, the total variation in the amount of light entering our eye from all the individual point sized sources will average out to zero, thereby nullifying the twinkling effect.

Advance sunrise and delayed sunset:-

Because of atmospheric refraction , the sun is visible to us about 2 minutes before actual sunrise and about 2 minutes after the actual sunset.

Scattering effect:-

• Spreading of light in various dieectidir as .by colloid particles.
• Scattering is inversely proportional to wavelength.
• Tyndall effect:- When light passes through colloid it's part becomes visible.
• This is called Tyndall effect.

Example :- 

Path of light becomes visible when light enters a dark and dusky room through a slit or ventilator.

Path of light becomes visible when light passes through dense canopy of trees in a forest.

Dependence of colour of scattered light:-

• If particles are very fine , the scatter mainly the blue colour of light (shorter wavelength)
• Medium sized particles scatter mainly the red colour (longer wavelength)
• Even  larger particles scatter all the colours of light that is why it appear white.
• Wavelength of red colour is about 1.8 time to that of blue light.
• Danger signs are made in red colour.
• Red is the least scattered colour. It is least scattered by fog and smoke and can be seen in same colour over a long distance. So danger signs are made in red colour.

Colour of sky appears blue on a clean day:- 

• The upper layer of atmosphere contains very fine particles of water vapours and gases.
• These particles are more effective in scattering of light of shorter wavelength mainly blue than longer wavelength. So the sky appear blue.

Appearance of sky to an astronaut in the space:- 

• The sky would appear dark to an astronaut in space as scattering is not very prominent at such high  attitude due to absence of particles (atmosphere)

Clouds appear white:-

•  clouds are formed by water vapours.
• Water vapours condense to form water droplets due to larger size of droplets , all colour of light are scattered and clouds appear white.

Colour of   Sun appear red during sunrise and sunset:-

• While sunset and sunrise , the sun is near horizon and sunlight has to travel larger distance in atmosphere.
• Due to this , most of blue light (shorter wavelength) are scattered away by the particles
• The light of longer wavelength (red colour) will reach our eye.
• Thats why sun appear red in colour.

Class 8th keywords

Chapter 1:- Crop production and management

1. Agricultural practice:-Various tasks performed by farmers for crop production are termed as Agricultural practices

2. Animal husbandry:-. Animals reared at home or in farms have to be provided with proper food, shelter and care. When this is done on a large scale, it is called animal husbandry.

3. Crop:-Crop is a plant that is grown on a large scale commercially.

Pulses, Cereals, Oil seeds, Vegetables & fruits are different types of crop.

4. Fertiliser:-Fertilizers are commercially produced plant nutrients. They result in higher yields & healthy plants, if applied in proper dose

5. Granaries:- Storehouse where large scale storage of grains is done  to protect them from pests like rats and insects.

6. Harvesting:-Harvesting is cutting of crop after it is matured. The season of harvesting brings a lot of happiness as this is time when the hard work of farmers brings results.

7. Irrigation:-Irrigation is artificial application of water to soil to ensure growth of agricultural crops.

8. Kharif:-Crops grown in rainy season are termed as Kharif crops. Examples: Maize, soyabean, sugarcane 

9. Manure:-Manure is an organic substance that increases soil fertility. It is prepared from decomposition of animal excreta & plant wastes.

10. Plough:-Tool used for ploughing . It is made of iron/ wood. It is pulled by a pair of animals like cows/ oxen/ horses and operated by the farmer through the handle

11. Rabi :-Crops grown in winter season are termed as Rabi crops. Examples: Wheat, Gram, Pea

12. Seeds:- the small hard part of a plant from which a new plant of the same kind can grow.

13. Silo:- Towers where large scale storage of grains is done  to protect them from pests like rats and insects.

14. Sowing:-Scattering seeds on the Earth after soil is prepared for cultivation is termed as Sowing

15. Storage:- Proper storage of food grains is important to protect against moisture, micro-organisms & insects.

16. Threshing:- In the harvested crop, the grain seeds need to be separated from the chaff. This process is called threshing. This is carried out with the help of a machine called combine which is a harvester as well as a thresher.

17. Weeds:-Weeds are unwanted plants in the cultivated field. They compete for nutrients, space, water & light, therefore, adversely affect crop growth.

18. Weedicides:-These are chemicals which kill weeds without damaging the crops.

19. Winnowing:-Threshing can be done manually using a process called ‘Winnowing’

In this process, grains are separated from chaff by throwing into the air. Chaff gets carried away by wind, while grains fall back.

Chapter :- 2 Micro-organisms friend and foe

1. Algae:- these are  multicellular,aquatic microorganisms  Example:-Spirogyra, Ulothrix, Chlamydomonas

2. Antibiotics:-Antibiotics are chemical substances that kill disease-causing microbes

3.Antibodies:- Proteins which are produce by our body to fight the invader.

4.Bacteria :- Bacteria are one of the oldest unicellular  life form that appear  appear in a variety of shapes & sizes (Spherical, elongated, spiral etc.)

5.Carrier:- Agents which carry pathogens to healthy person. Ex :- female anopheles mosquito , female Aedes

6.  Communicable diseases:- Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable disease . Ex cholera, common cold, chicken pox and tuberculosis.

7. Fermentation:- The process of conversion of sugar into alcohol is called fermentation.

8. Fungi:-Fungi are multicellular, Heterotrophic, immobile life form that found in moist and humid climate.

9. Lactobacillus:-Curd contains a bacterium, Lactobacillus

It is a friendly-bacterium

10. Micro-organisms:- organism which are too small to see with naked eyes. They can be seen with microscope or magnifying glass.

11. Nitrogen cycle:- Nitrogen cycle is all about the movement of nitrogen between various elements on Earth 

12. Nitrogen fixation:- The process of fixing atmospheric nitrogen into soil by nitrogen fixers is called nitrogen fixation.

13. Pasteurization is a technique that makes use of heat & cold treatments to preserve food items. In this process, milk is heated to about 700C for 15-30 sec & then suddenly chilled & stored. This technique was invented by Louis Pasteur (1864).

14 Pathogen: disease-causing organisms are called Pathogens.  Pathogens include bacteria, viruses, fungi & protozoa.

15. Preservation:- The process of protecting food from the attack of microorganisms is called preservation

16. Protozoa:- Group of single celled organisms  like Amoeba, Paramecium etc is called Protozoa

17.Rhizobium:- Nitrogen fixing bacteria which is present in the roots on leguminous plants us called rhizobium

18:- vaccine:-vaccine is a biological preparation that resembles a disease causing microbe. These vaccines are made up of dead or very weak microbes.

19. Virus:-microorganisms which behave like non-living when outside host cell, and reproduce only when inside the host cell

20. Yeast:- A single celled organism which helps in fermentation .

Chap 3 synthetic fibres and plastics

1. Acrylic :-synthetic fibre which is formulated from a polymer called polyacrylonitrile.It is lightweight, soft, warm, and has resemblance with wool. 

2. Artificial silk :- The fibre that is obtained by chemical treatment of wood pulp is called artificial silk Or rayon.

3. Nylon:- Synthetic fibre that is prepared from coal, water and air. It is the first fully synthetic fibre.

4. Plastic :- A light , strong and durable polymer that is used to make chairs , slippers, decoration pieces etc.

5. Polyester:- Synthetic fibre that doesn't get wrinkled easily.

6. Polymer :- Many small units combine together to form a large single unit called polymer

7. Polythene :- A type of plastic which is formed by combination of many ethene molecules.

8. Rayon :- The fibre that is obtained by chemical treatment of wood pulp is called artificial silk Or rayon

9. Synthetic fibres :- Man made fibre is called synthetic fibre. Ex:- Nylon , Rayon, polyester and acrylic etc.

10. Terylene :- It is a kind of polyester that can be drawn into very fine fibres that can be woven like any other yarn

11. Thermoplastics :- The plastic which gets deformed easily on heating and can be bent easily are known as thermoplastic

12. Thermosetting plastic :- The plastic which donot gets deformed easily on heating and can be bent easily are known as thermoplastic

Chap 4:- Materials: Metals and Non metals

1. Atom :- The smallest unit of matter which contains electron , proton and neutron as subatomic particles.

2. Conductor :- The substances which allow electricity to pass through it . Example:- metals are good conductors .

3. Displacement reaction :- A reaction in which a more reactive element displace less reactive element from its salt solution. Example:- Iron + Copper sulphate --> Iron sulphate + copper.

4. Ductility :- The ability of metals to be drawn into thin wires is called ductility. Example:- Gold is most ductile metal.

5. Elements :-  Pure species which is made up of only one kind of atoms.

6. Hardness :-   The ability of a substance to resist cutting and grinding is called hardness. Metals are generally hard. The hardness varies from metal to metal . Except :- lithium, sodium, potassium.

7. Malleability :- Some metals can be beaten into sheets. This property is called malleability. Example:- gold and silver are the most malleable metals

8. Metals :- Substances which are electropositive in nature i.e. they have a tendency to lose electrons. Example:- Sodium, iron, copper, gold, silver, etc.

9. Metalloids :-  The elements which have properties in between metals and non metals. Example:- boron, silicon etc.

10. Non metals :- Substances which are electronegative in nature i.e. they have a tendency to gain electrons. Example:- Carbon, Sulphur, Iodine, Oxygen, Hydrogen etc.

11. Sonorous :-  Metals produce ringing sounds this property is called sonorous.

Chap 5 :-  Coal and Petroleum

1. Coal :- A black coloured hard substance that is composed of carbon, hydrogen, nitrogen, oxygen, minor amount of sulphur.

2. Coal gas :- It is a gaseous mixture of hydrogen, methane, and carbon monoxide

3. Coal tar :- Black, thick and viscous liquid that contains 42% carbon, 48% hydrocarbons and rest of the percentage is occupied by water

4. Coke :-  Hard, black coloured and porous derivative of coal.It is a pure form of carbon with less content of impurities and has high carbon content.

5. Fossil fuels:- Fossil fuel refers to the deposits of organic materials, formulated from dead plants and animals under several thousand feet of silt. It's formation takes millions of years

6. Natural gas:- It is a cleaner fuel that is stored under high pressure as compressed natural gas.

7. Petroleum :- It is a clear, green or black coloured oily liquid matter  that can be either thin like gasoline or thick like tar.

8. Petroleum refinery :- Process of separation of the wide variety of constituents of petroleum is called Refining of Petroleum carried out in petroleum refinery

Chap 6 :- Combustion and Flame

1. Acid Rain :- Oxides of sulphur and nitrogen dissolve in rain water and form acids . Such a rain is Called acid rain.

2. Calorific value:- Amount of heat energy produced on complete combustion of 1Kg of a fuel is called calorific value. It's unit is KJ/kg

3. Combustion :- A chemical process in which a substance reacts with oxygen to give off heat is called combustion.

4. Deforestation :-  Clearing of forests(by cutting down forest trees)over a wide area is called deforestation.

5. Explosion :- The combination which is accompanied by heat, light and sound is called explosion.

6. Flame :- The visible gaseous part of fire which is hot, glowing ignited gas during combustion is called flame.

7. Fire extinguisher :-The job of a fire extinguisher is to cut off the supply of air or bring down the temperature of the fuel.

8. Fuel :- Combustible substance which release enough heat energy to be used for domestic and industrial purposes. Example :- LPG, CNG, Wood, Coal, petroleum etc .

9. Fuel efficiency:- The amount of heat produced by the complete combustion of unit mass of a fuel is known as fuel efficiency.

10. Global warming:- Rise in the temperature of the atmosphere of the earth  due to production of acidic oxides during combustion of fuel is called global warming.

11. Ideal fuel :- The fuel which is cheap, easily available, have low ignition temperature ,high calorific value and doesn't produce residue is called ideal fuel.

12. Ignition temperature :- Lowest temperature at which a substance catches fire is called ignition temperature.

13. Inflammable substances  The substances which have very low ignition temperature and can easily catch fire with a flame is called inflammable substances.

Chap 7 :- Conservation of Plants and animals

1. Biodiversity:- the existence of a number of different kinds of animals and plants which together make a good and healthy environment

2. Biosphere reserve:- biosphere reserve is a place where animals and some species of plants are kept safely.

3. Deforestation :- This process of removal of a forest or collection of trees from a land and thereafter converting the land to a non-forest use is called deforestation.

4. Desertification :- When a fertile land gets converted to a barren land by deforestation, this is called desertification

5. Ecosystem :- All the interacting organisms in an area together with non-living constituents of the environment forms an ecosystem.E.g. Forests, ponds.

6. Endangered species:- The species of plants and animals whose number is reducing to a level where they may no more exist in nature are called Endangered species

7. Endemic species :- The species of plants and animals that can be found only in a specific region are called Endemic species

8. Extinct :- The species of plants and animals that no more exist in nature due to unsuitable habitat are called Extinct species. 

9. Fauna :- The animals of a particular region are called fauna of that region

10. Flora :- The plants of that region are called flora of that region

11. Migratory birds:- Birds that travel from their own habitat to a different habitat due to several reasons at a certain period of the year.

12. National park :- Protected areas intended to provide a natural habitat with all natural resources to the animals where they can freely roam and use the habitat are called national park.

13. Red data book :- The source book that is used to keep a record of endangered species of plants, animals and other species existing within the territory of the state or country is called red data book.

14. Reforestation :-  the act of planting new trees in an area or region where they were cut down previously

15. Sanctuary :- a place where birds or animals are protected from being hunted

Chap 8 :- Cell - Structure and Functions

1. Cell:- Cell is the structural and functional unit of life

2. Cell membrane:- Thin , delicate, living and outermost membrane which bound cytoplasm.

3. Cell wall:- Non-living , rigid, outermost covering of plant cell which is fully permeable.

4. Chloroplast:- Green colour plastid which contain chlorophyll.

5. Chromosome:- Rod shaped structure that formed when chromatin condense together when the cell is about to divide

6. Cytoplasm:- Jelly like structure present between the cell membrane and the nucleus.

7. Eukaryotes:- Organisms whose cells have well organised nucleus with a nuclear membrane

8. Gene:-Unit of inheritance in living organisms which control the transfer of a hereditary characteristics from parent to offspring.

9. Multicellular:- organisms made up of more than one cell are called multicellular organisms

10. Nuclear membrane:- Double layered covering of nucleus which separate material inside nucleus from cytoplasm

11. Nucleolus:- Structure embedded in nucleoplasm and compose of proteins and RNA

12. Nucleus:- A structure which is present near centre of eukaryotic cell.

13. Organ:- Group of tissue together make functional unit called organ

14. Organelles:- Membrane bound structure due to which a cell is able to live and perform all its functions

15. Plasma membrane:- Thin, delicate, living outermost covering of cell which ensure protection of cell

16. Plastid :- Organelles present in plant cells only and provide colour and store food to it

17. Prokaryotes:- Organisms whose cells have nuclear material without nucleus membrane

18. Pseudopodia:- False finger like projection which Amoeba possess for intake of food

19. Tissue:- Group of cell which have common origin and perform same function is called tissue

20. Unicellular:- Single celled organism is called unicellular 

21. Vacuole:- Organelles which store food and is surrounded by tonoplast

22. White blood cell (WBC) :- Blood cells which fight against germs 

Chap 9 :- Reproduction in animals

1. Asexual reproduction:- The type of reproduction in which only a single parent is involved is called asexual reproduction

2. Binary fission:- A mode of asexual reproduction in which an organism reproduce by dividing itself into two is called binary fission. Ex:- Amoeba

3. Budding:- A mode of asexual reproduction in which new individuals develop from buds is called budding. Example:- Hydra

4. Eggs:- the ovary produces female gamete called egg or ovum

5. Embryo :- The  zygote divide and redivide to form groups of cells that develop into different tissues and organs of the body. This developing structure is termed as an embryo.

6. External fertilization:- Fertilization that takes place outside the female bodies is called external fertilization

7. Fertilization:- The fusion of ovum and sperm is called fertilization

8. Foetus :- The stage of the embryo in which all the body parts are identifiable is called foetus

9. Internal Fertilization:- Fertilization that takes place inside the female body is called internal fertilization

10. Metamorphosis:- The transformation of the larva  into adult through drastic changes is called metamorphosis

11. Oviparous Animals:- Animals such as hen, frog, lizard and butterfly which lay eggs are called oviparous animals

12. Sexual Reproduction:- Reproduction resulting from the fusion of male and female gametes is called sexual reproduction.

13. Sperms :- The testis produce male gametes called sperm

14. Viviparous animals:- Animals such as human beings, cows and dogs which give birth to young ones are called viviparous animals

15. Zygote :- The fertilized egg is called zygote

Chap 10 :- Reaching the age of Adolescence 

1. Adam's apple :- At puberty, boys grow a larger voice box that appears as a bulging part of the throat. This is called Adam’s apple.

2. Adolescence :- period of life in which organism  become capable to reproduce their offsprings.

3. Adrenalin :- Hormone  that helps to adjust stress in a human body at the time of certain emotions like anger, embarrassment, etc. It is secreted by Adrenaline gland.

4. Balanced diet :- Balanced diet is a meal that includes adequate amount of proteins, carbohydrates, fats, vitamins and minerals.

5. Endocrine glands :- Ductless hormones which secrete hormones and released it into the bloodstream 

6. Estrogen:- Female sex hormone that is secreted by ovaries.

7. Hormones:- Chemical substances that coordinate the activities of living organisms and also for their growth are called hormones.

8. Insulin:- Hormone produced by pancrease is called insulin.

9. Pituitary gland:- Gland which controls the release of other hormone glands in a human body, including the thyroid and adrenals, the ovaries and testicles.

10. Puberty:- The period in which rate at which general body growth begins to slow down and reproductive tissues begin to mature is called puberty.

11. Reproductive health:- A state of complete physical, mental and social well being in all aspects of reproduction.

12. Secondary sexual characters:- Secondary sexual characters refer to the external features that distinguish a male from a female.

13. Sex chromosomes:- The sex of baby is determined by a pair of chromosome called sex chromosomes.

14. Target site:- Endocrine glands release hormones into the bloodstream to reach a particular body part called target site.

15. Testosterone:- Male sex hormone that is secreted by testis

16. Thyroxine:- Hormone produces by thyroid gland is called thyroxine.

17. Voice box :- Sound box or larynx which begins to grow at puberty . It produces sounds.

Chapter 11 Force and Pressure

 1. Atmospheric pressure:-  The air all around us also exerts pressure. This is known as Atmospheric  Pressure. The value of atmospheric pressure is very high.

2. Contact forces : Force that arises with the contact of 2 or more objects involved. Examples : Muscular force and Frictional Force

3. Electrostatic force is the force exerted by a charged body on another charged or uncharged body. 

4. Force:-A push or a pull on an object is called a Force

5. Frictional Force is a force that acts on all moving objects by the surface which it is in contact with. 

The Frictional force is always in the direction opposite to the applied force.

6. Gravitational : it is an attractive force between two massive bodies .

G= (gmM)/r2

7. Gravity:-force exerted by the earth on all objects on it. When a ball is thrown up, it falls to the ground because of gravity

8. Magnetic Force is a force that attracts certain metal objects (like iron and iron filings) towards a magnet.

9. Muscular force is the type of force wherein we use our physical strength to change the state of motion of an object. Eg: Man pushing a car, Bullocks pulling a cart of load, Cycling, Weight Lifting

10. Non-contact forces: Forces that arise without the contact of 2 or more objects involved. Examples: Magnetic Force, Electrostatic Force, Gravitational force

11. Force acting on unit area is called Pressure ie Pressure =   Force/Area

12. Pull:-Pull refers to that force which tends to 'move the object towards'  the direction of the force applied.

13. Push:-

Push refers to the force which tends to 'move the object away'  from the direction of the force applied

Chap 12 :- Friction

1. Ball bearing :- Ball bearing is a device which consists of a ring of small metal balls. It is designed to make the moving parts of a machine to roll over each other rather than slide.

2. Drag :- Fluids (means liquids and gases) too  exert friction on the objects. The frictional force exerted by fluids is called a drag

3. Fluid friction :- Fluids (means liquids and gases) too  exert friction on the objects. The frictional force exerted by fluids is called fluid friction or drag

4. Friction:- Friction is a type of forces that opposes motion.It always acts in a direction opposite to that of the applied force.

5. Interlocking:- The irregularities on two surfaces tend to lock into each other . This is called interlocking.

6. Lubricants:- substances which make the surfaces smooth and thereby reduce friction  are called lubricants.  

7. Rolling friction:- when a body rolls over another surface is called Rolling Friction. The Rolling Friction is less that Sliding Friction.

8. Sliding friction:- when a body moves over another surface  is called Sliding Friction

9. Static friction :- Static friction is friction between two or more solid objects that are not moving relative to each other. 

Chap 13:- Sound

1. Amplitude:- The magnitude of maximum disturbance in the medium on either side of the mean value is called amplitude.

2. Audible:- A sound of 20Hz to 20,000 Hz that a human can hear is called audible range of sounds.

3. Eardrum:- The thin membrane present in the ear is called eardrum.

4. Hertz:- SI unit of frequency is called hertz

5. Larynx:- sound is produced by the vibration of an organ called voice box or larynx. 

6. Loudness:- Amplitude determines the Loudness of sound. It is expressed in a unit called decibel (dB).

7. Noise:- Unpleasant sounds are  called noise 

8. Oscillation:- The motion in which object moves to and fro is called oscillation.

9. Pitch :-Perception of frequency of sound wave is called stillness of pitch. Frequency determines the shrillness or the pitch of the sound. 

10. Shrillness:- Perception of frequency of sound wave is called stillness of pitch. Frequency determines the shrillness or the pitch of the sound. 

11. Time period:- Time taken to complete one oscillation is called time period.

12. Vibration :- Rapid to and fro motion of an object is called vibration.

13. Voice box :- sound is produced by the vibration of an organ called voice box or larynx. 

14. Wind pipe :- Pipe which help in gases exchange. The Larynx is situated at the upper end of windpipe.

Chap 14 Chemical effects of electric current

1. Electrode:-Electrodes are the metal rods which are dipped in liquids, to which cells are attached are called electrodes

2. Electroplating:-Process by which metals are coated with another metal to give it their lustrous appearance and still keep it cost effective.

Or 

Process of depositing a layer of desired metal on another material by mean of electricity is called electroplating.

3. Good conductor:-The materials which conduct electricity are called good conductors of electricity. Eg: Iron, copper, aluminum, iron, human body etc

4. LED:- Light Emitting Diode.  A device that produces a light on electrical and electronic equipment.

5. Poor conductor:-The materials which don't conduct electricity at all are bad conductors of electricity. Eg: plastic, glass, rubber.

Chap 15  Some Natural Phenomenon

1. Crust :- The uppermost layer of the earth is called crust.

2. Discharge:- The process of release of electric charges from a charged object to an uncharged object in contact with it , is called discharge.

3. Earth's plates:- The outermost layer of the earth is not in one piece but is fragmented . These fragments are called earth's plates

4. Earthquake:- It is a sudden shaking or trembling of the earth which lasts for a very short time is called earthquake

5. Electroscope:- A device that can be used to test whether an object is carrying charge or not , is called electroscope.

6 . Lightning:- The bright flash of light which we see in the clouds is called lightning. 

Or

Lightning is an electric discharge in the atmosphere between oppositely charged clouds 

7. Lightning conductor:- Lightening conductor is a device used to protect buildings from the effect of lightening.

8. Negative charge:- If an object gains electrons, it now has surplus number of electrons. Thus, this object becomes negatively charged.

9. Positive charge:-  If an object loses some electron, it is left with surplus number of protons. Thus, this object becomes positively charged.

10. Richter scale:- The power of an earthquake is expressed in terms of a magnitude on a scale clleca the Richter scale

11. Seismograph:- An instrument which record seismic waves produce by tremors.

12. Thunder:- Thunder is the sound caused by lightning

13. Thunderstorm:-  A rain-bearing cloud that also produces lightning is called thunderstorm.

14. Transfer of charge:- When certain objects are rubbed against another object, electrons may get transferred from one object to another.

15. Tsunami:- A tsunami is a very large and powerful wave. It is caused by earthquakes under the sea.

16. Tremor:- A relatively minor seismic shaking or vibrating movement.

Chap 16 light

1. Angle of incidence:-angle between the Incident ray and normal

2. Angle of reflection:-Angle between the reflected ray and normal

3.Blind spot:- Spot where rod and cone cells are absent so no image formed.

4. Braille:-The Braille script is an alphabet set used by the blind for reading and writing. Each Braille character is made up of a combination of 6 dots arranged in a matrix form.

5. Cones:-cells which are Sensitive to bright light

6. Cornea:-Outermost, transparent, thin membrane of eye ball.

Light enters into eye through cornea.

7. Diffusion or irregular reflection:-

When light falls on a rough surface (like a stone, your body, your clothes etc), all the parallel incident rays are not reflected parallel to each other. This is called Diffused Reflection. 

8. Incident rays:-Ray of light that strike the surface.

9. Iris:-Dark muscular diaphragm that control the size of pupil.

Provide colour to eye.

10. Kaleidoscope:-A kaleidoscope  is an optical instrument with two or more reflecting surfaces tilted to each other in an angle, so that one or more (parts of) objects on one end of the mirrors are seen as a regular symmetrical pattern when viewed from the other end, due to repeated reflection.

11. Lateral inversion:- In mirror left appears right and right appears left . This is called lateral inversion

12. Laws of reflection:-1. Angle of incidence= angle of reflection

2. Incident ray, reflected ray and the normal all lie on the same plane.

13. Pupil:It is the window of the eye.

Central aperture In iris.

Regulates and control the amount of light entering the eye

14 Reflected rays:-Ray of light sent back by the surface after reflection

15. Reflection:-Bouncing back of ray of light into the same medium after striking a polished surface such as mirror is called reflection of light

16 Regular reflection:- When light falls on a smooth uniform surface (like a mirror), all the parallel incident rays are reflected perfectly parallel. This is called Regular Reflection. 

17 Retina:-Delicate membrane having enormous number of light sensitive cells. Lens  image form on the retina.

18 Rods:- cells which are Sensitive to  dim light

Chap 17 Stars and the solar system

1. Artificial Satellites:- Man made satellites revolving round the Earth are called artificial satellites

2. Asteroids:- large gap in between the orbits of Mars and Jupiter that is occupied by a large number of small objects that revolve around the Sun are called asteroids

3. Cassiopeia:- constellation in the notthern sky that looks like a distorted letter W or M

4. Celestial objects:- the stars , the planets, the moon and many other objects in the sky are called celestial objects.

5. Comets:- Comets are cosmic snowballs of frozen gases, rock and dust that orbit the Sun. 

6. Constellations:- Group of stars that appear to form recognisable shapes.

7. Light year:- It is the distance travelled by light in one year.

8. Meteorites:- meteors that reaches the Earth is called a meteorite

9. Meteors:- Bright streaks of light in the sky or shooting stars are called meteors

10. Natural satellites:-  A natural satellite is any celestial body in space that orbits around a larger body. 

11. Orbit:- A planet has a definite path in which it revolves around the Sun . This path is called an orbit.

12. Orion:- constellation which has seven or eight bright stars. It is also called the hunter 

13. Phases of moon:- The various shapes of the bright part of the moon as seen during a month are called phases of the moon.

14. Planets:- Celestial bodies that revolves around the Sun in a fixed path, are called planets

15. Pole star:- Pole star is the only star in the sky which appears stationary to an observer on Earth.

16. Remote sensing:- Remote sensing is the science of obtaining information about objects or areas from a distance, typically from aircraft or satellites.

17. Solar system:- A collection of the Sun, eight planets , asteroids ,comets and meteors.

18. Stars:- Stars are huge celestial bodies made mostly of hydrogen and helium that produce light and heat.

19. Ursa Major:- There are seven prominent stars that appears like a big ladle or a question mark is called Ursa major.

Chap 18 Pollution of Air and Water

1. Air pollution :- It is defined as contamination of air by impurities which may have a harmful impact on the living organisms and non living components.

2. Chemical contamination :- When industries release chemicals including arsenic , lead and fluoride into waterways , it is called chemical contamination. This leads to toxicity in plants and animals.

3. Global warming:- the average temperature of the  earth atmosphere is gradually increasing. This is called global warming.

4.Green  house effect:- The trapping of radiations by the earth's atmosphere is similar to that of green house. So the effect is called green house effect

5. Pollutants:- those substance which contaminate air and water.

6. Potable water:- water which is purified and fit for drinking is known as potable water.

7. Water pollution:-  It is the contamination of water by substances harmful to life