NOTES: SCIENCE(old) CLASS 8 PUNJAB TEXT BOOK BOARD LAHORE PAKISTAN 2014

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NOTES: SCIENCE (old) CLASS 8 PUNJAB TEXT BOOK BOARD LAHORE PAKISTAN 2014

CH:1 CLASSIFICATION OF LIVING ORAGNISMS P: 7-8

Q No.3 ENCIRCLE THE CORRECT ANSWER IN THE FOLLOWING:

i-          Viruses are considered as living organisms because(a)       Can be crystallized

(b) Can be observed with electron microscope

(c) They are of different shapes

(d) They can reproduce

ii-         Tell the name of disease caused by virus in the following(a)T.B. (b)    Typhoid     (c) Dysentery     (d) Polio
iii-       The disease caused by bacteria is(a)Measles (b) Small pox       (c)   Cholera   (d) AIDS
iv-       Bacteria which produce diseases in plants and animals are called(a)Heterotrophic bacteria (b) Autotrophic bacteria                (c) Parasitic bacteria      (d) Pathogenic bacteria
v-         In Pasteurization, milk is heated at(a)62°C for half an hour        (b) 62°C for 15 seconds

(c) 71°C for half an hour (d) 100°C for one minute

 

Ans: (i-d) (ii- d) (iii-c )   (iv- d ) (v-a)

 

QUESTION No.4 GIVE SHORT ANSWERS:

Q No.iDefine classification and species?
ANS:CLASSIFICATION:

The systematic grouping of organisms into categories on the basis of evolutionary or structural relationships between them; taxonomy.

SPECIES:

A fundamental category of taxonomic classification, ranking below a genus or subgenus and consisting of related organisms capable of interbreeding.

Q No. iiWrite down names of four diseases of man caused by viruses.
ANS:1.    Measles

2.    Influenza

3.    Cold

4.    Small pox

5.    Polio

Q No.iiiWrite down names of four bacterial diseases of man.
ANS:a-    T.b.

b-    Whooping cough

c-    Diphtheria

d-    Typhoid

e-    Pneumonia

Q No. ivWhat is a difference between Sterilization and Pasteurization?
ANS:STERILIZATION:

The process in which food and other things are preserved by heating from 120°C to 126°C for 12 – 90 minutes under suitable pressure and makes the food free from pathogens.

PASTEURIZATION:
The process in which milk is heated for half an hour at 62Qc or for 15 seconds at 71 “c to make it free from bacteria.

 

QUESTION No.5Why is classification of living organisms necessary?
ANS:The classification of living organisms is necessary to know there salient features and characteristics. The classification of organisms is important because:

1-    To classify means to put things into groups.

2-    Classifications systems make communication in science easier by having just one name for each organism.

3-    It also helps to organize information about organisms and their needs.

4-    Keeps scientist from giving two different names to an organism.

5-    A classification system lists organisms in a series of groups;

Kingdom, phylum, class, order, family, genus and species.

QUESTION No.6″Micro-organism is a diverse group of living organisms.” Explain.
ANS:MICRO-ORGANISM:

Micro means small and organisms means living things.

Micro-organisms are those organisms that are so small and they cannot be seen with naked eye.

In order to observe them, we need a light microscope or an electron microscope.

Micro-organism form diverse group which includes different kinds of organisms, viruses, plants and animals, certain algae and some fungi.

Micro-organisms differ from one another with regard to structure and mode of nutrition.

FOR EXAMPLE:

1-    On the basis of structure viruses are not cellular while other micro-organisms are cellular.

2-    Bacteria are unicellular but they have no organized nucleus while other micro-organisms have organized nucleus.

3-    According to mode of nutrition algae and a few bacteria are autotrophs while fungi and most unicellular animals are heterotrophs.

Due to these characteristics micro-organisms form a diverse group which includes different kinds of living organisms.

 

CH:2 PLANT KINGDOM P: 17-18

 

Q No.3 ENCIRCLE THE CORRECT ANSWER IN THE FOLLOWING:

i-              The group of plants which includes heterotrophs(a)Algae(b)          fungi (c)         Mosses(d) Ferns
ii-             The group of plants which includes plants without vascular tissues?(a) Mosses (b)           Ferns (c) Conifers (d) Flowering plants
iii-            Rice plant belongs to the group of plants(a)Mosses (b) Ferns       (c) Conifers   (d) flowering plant
iv-            Plants prepare their own food through photosynthesis are called(a)Parasites (b) Saprotrophs (c) Heterotrophs (d) Autotrophs
   v- Which of the following group of plants consisting to thread like hyphae(a)     Algae (b) Fungi (c) Mosses (d) 100°C for one minute
Ans: (i-b) (ii-a ) (iii- d ) (iv- d )   (v-b )

 

QUESTION No.4 GIVE SHORT ANSWERS:

Q No.iWrite down two characteristics of ferns.
ANS:1-    Ferns are non-flowering plants which do not produce fruits and seeds too.

2-    Ferns possess vascular tissues i.e. xylem and phloem.

Q No. iiWhat are the differences between mosses and ferns?
ANS:
MOSSES FERNS
(i) Mosses are non-vascular plants. (i) Ferns are vascular plants.
(ii) In mosses gametophyte is dominant generation. (ii) In ferns strophes generation is dominant.
(iii) Saprophyte is depended gametophyte. (iii) Both saprophyte and gametophyte generation are independent.
Q No. iiiGive two differences between Dicots and Monocots?
MONOCOTS DlCOTS
01 Monocots have only one cotyledon in their seeds. Dicots have two cotyledons in their seeds.
02 Monocots have long and narrow leaves Dicots have broad leaves with
Q No. ivDefine decomposers?
ANS:Decomposers are organisms which convert the dead organic matter into simpler form i.e. fungi and bacteria etc.

 

QUESTION No.5Write down the names of different groups of non-flowering plants? Describe salient features of each group and give examples.            
ANS:ALGAE:

             Algae are the simplest group of plant kingdom. They are found in fresh water and seas. As regards to structure, algae are both unicellular and multi-cellular. Cells of algae contain nucleus
and other structures. Algae are autotrophs.

Examples: Chlamydomonas and spirogyra.

FUNGI:

Fungi are composed of numerous thread like structures (hyphae). According to mode of nutrition, fungi are hetrotrophs. They decompose dead organic matter. Few fungi causes diseases like Athletes foot and king worm in men.

Examples: Rhyzopus and mushrooms.

MOSSES:

Mosses are found in cool, moist and shady places. They live both in water and on land.
Mosses have only roots, stem and leaves structures instead of them. Vascular tissues are absent in mosses.

Examples: Polytrichum and Funeria.

FERNS:

They are adopted to live in cold, shady and humid places. They have well-developed roots stems and leaves. Vascular tissues present in ferns.

Examples: Drypteris, Pteris and Adiantum.

CONIFERS: (Evergreen)

Conifers are found in colder regions and hilly areas. They have prominent roots, leaves and stem. The leaves are long, narrow and needle like.

Seeds of conifers are present in the form of a cone. Vascular tissue (zylem &phloem) are present in them.

Examples: Deodar, Pines, Saroo and Thuja{Moor Punkh)

QUESTION No.6Classify flowering plants. Describe salient features of each group and give examples?
ANS: Flowering Plants:These are vascular plants and produce fruits and seeds. New plants develop from their seeds.

HABITANT:

These plants are formed in plains and can adapt to all types of environment.

STRUCTURE:

Flowering plants are found in the form of herbs, shrubs and trees.

CLASSIFICATION of FLOWERING PLANTS:

Flowering plants are divided into two groups on the basis of the number of cotyledons in the seed:

Dicotyledonous (Dicots)

Monocotyledon{Monocot)

DICOTS: Those plants, which have two cotyledons in the seeds are called Dicots.

Their leaves are usually broad.

Examples: Peas, Rose, Sunflower, Apple, Sarson, Mango etc.

 

CH:3 ANIMAL KINGDOM P: 31-32

 

Q No.3 ENCIRCLE THE CORRECT ANSWER IN THE FOLLOWING:

(i)Following animal is parasite

(a)      Amoeba (b) Tapeworm     (c)           Mosquito    (d)           Snail

(ii) Name the animal has jointed legs

(a)   Jelly fish                                                        (b)       Butterfly                                                       (c)Octopus                                                    (d)               Starfish

(iii)The group of animals belongs to cold blooded animals

(a)         Fishes, amphibians, birds (b) Fishes, amphibians, reptiles                                                             (c)Fishes amphibians, mammals     (d)Fishes, reptiles, birds

(iv) The group of animals belongs to warm blooded animals

(a)     Fishes and birds    (b)           Fishes and mammals                                                                     (c)           Fishes and reptiles (d) Birds and Mammals

Ans: (i-b) (ii- b) (iii- c ) (iv-d   )

 

QUESTION No.4 GIVE SHORT ANSWERS:

Q No.iWrite down two characteristics of mammals?
ANS:1-   Mammals have hair on their bodies.

2-   They have fleshy external ears.

Q No. iiWhat is the difference between cold blooded and warm blooded animals?
ANS:COLD BLOODED ANIMALS:

Animals which cannot maintain their body temperature with respect to their environment are called cold blooded animals.

For example, Fish, amphibians and reptiles etc.

WARM BLOODED ANIMALS:

Animals which can maintain their body temperature with respect to their environment are called warm blooded animals.

For example; Birds and mammals etc.

Q No.iiiWrite names of two parasites which are found in man?
ANS:(a) Endameba: It causes dysentery in human beings.

(b)       Malarial parasite: It caused malaria in human beings

Q No. ivWrite differences among flat worms, round worms and segmented worms?
ANS:FLAT WORMS:

                       Flat worms are flat body like ribbon shaped e.g. liver fluke, tape worm etc.

ROUNDED WORMS:

Round worms rounded body worms having both the ends pointed e.g. Askers, hook worm etc.

SEGMENTED WORMS:

Their body is segmented e.g. earth worm, leach, aeries etc.

 

QUESTION No.5Describe salient features of fishes and give examples?
ANS: SALIENT FEATURES of FISHES:Fishes (aquatic animals), are found in water.

STRUCTURE: Body of fishes consists of three parts;

(1)Head (2) Trunk (3) Tail

FINS: Fins are present on the trunk region of their body.

SCALES: In the most cases, body of fishes is covered by slimy scales.

Examples: Shark, Rohu, and Trout

QUESTION No.6Describe salient features of animals with jointed legs and give examples?
ANS: SALIENT FEATURES of JOINTED LEGS ANIMALS:Animals of this group possess jointed legs on their bodies.

HABITANT: these animals are found in water, air and on land.

CLASSIFICATION: animals with jointed legs are classified into two sub-groups.

(a) Insects

(b) Worm (like animals)

INSECTS: Body of insects is divided into three parts;

Head, Thorax, Abdomen

Examples: Butter-fly, Grass hopper etc.

Worm (like animals): The body of these worms is segmented. On every segment, there is one or two pairs of legs are present.

Examples: Centipedes, Millipedes

 

 

 

CH:6 SYMBOLS &FORMULAE P: 59-61

Q No.3 ENCIRCLE THE CORRECT ANSWER IN THE FOLLOWING:

(i) Cobalt is an element, its symbol is
(a)       C         (b)         CO   (c)     Cu             (d)Co
(ii) Ionic formula tells us the;
   (a) actual ratio which exists between all atoms.(b) total number of atoms.

(c) simplest ratio present between different atoms.

(d) all the above statements are true.

(iii) The number of elements found naturally, are:
               (a)     90           (b)         88     (c)     98             (d)109
(iv) Which one does not exist as a molecule?
               (a)           H2       (b)Cl2               (c)Be                 (d)Ne
(v) The formula of calcium carbonate is
             (a) KCO3  (b)     K2CO3 (c) CuCO3 (d)CaCO3
(vi) If valency of oxygen is 2 and that of aluminium is 3 then the formula of aluminium oxide will be
(a)             AlO     (b)     Al3O2         (c)   AlO2             (d)Al2O3

 

Ans: (i-d) (ii- c) (iii- a ) (iv- c )   (v- d) (vi-d )

 

QUESTION No.5Tell the total number of atoms in each of the following compounds?

(i) NH4CI (ii)H2S04 (iii)Fe2 (S04)3 (iv) Ca3(PO4)2

ANS: (i) NH4CI =13(ii)H2S04 =17

(iii)Fe2 (S04)3 =7

(iv) Ca3(PO4)2=6

QUESTION No.8Write down the symbols and charges present on the radicals given below?

Carbonate, Nitrate, Hydrogen carbonate, Sulphate, Phosphate, Chloride, Copper, Sodium, Ferrous, Chromium, Silver, Magnesium.

ANS:
RADICALS Symbols & Charges
1 Carbonate C032-
2 Nitrate N031-
3 Hydrogen Carbonate HC031-
4 Sulphate 52-
5 Phosphate PO43-
6 Chloride C11-
7 Copper Cu1+
8 Sodium Na1+
9 Ferrous Fe3+
10 Chromium Cr3+
11 Silver Ag1+
12 Magnesium Mg2+
QUESTION No.9Write down the formula of the following compounds?

Ammonium chloride, Aluminium phosphate, Calcium nitrate, Sodium phosphate, Barium carbonate, Zink chloride, Ammonia, Methane.

ANS:
Compounds Formulae
1 Ammonium chloride NH4CI
2 Aluminium phosphate Al2(SO4)3
3 Calcium Nitrate Ca(NO3)2
4 Sodium phosphate Na3PO4
5 Barium Carbonate BaCO3
6 Zinc Chloride ZnCI2
7 Ammonia NH3
8 Methane CH4

 

CH: 7CHEMICAL CHANGE&CHEMICAL BONDS P:73-75

QUESTION No.5Define ionic bond? Give an example to explain its formation?
ANS:IONIC BOND:

The bond formed by transference of one or more electrons from one atom to another atom is called an ionic bond.

Example:

Sodium atom transfers one of its electrons to chlorine atom and as a result, sodium ion (Nacl) and chloride ion (CI1-) are formed.

N a————– N a + + e

Sodium atom Sodium ion

CI+ e ——-Cl-

Calcium atom——-Calcium ion

Na + +cr———- Na Cl

QUESTION No.6What is a covalent bond? How do hydrogen atoms form a covalent bond?
ANS:COVALENT BOND

             The force of attraction which hold the atoms together by mutual sharing of electrons.

HYDROGEN–A COVALENT BOND:

Hydrogen gas exists in the form of diatomic molecules. Two hydrogen atoms in every hydrogen molecule are held together by mutual sharing of electrons. This mutual sharing of electrons is shown as follows:

H. + x H –. H» H –. H – H

The pair of electrons which exist between hydrogen atoms is known as shared pair of electrons.

QUESTION No.7What is the difference between an ionic bond and a covalent bond?
ANS:

Covalent Bonds Ionic Bonds
What is it? Covalent bonding is a form of chemical bonding between two non metallic atoms which is characterized by the sharing of pairs of electrons between atoms and othercovalent bonds. Ionic bond, also known as electrovalent bond is a type of bond formed from the electrostatic attraction between oppositely charged ions in a chemical compound. These kinds of bonds occur mainly between a metallic and a non metallic atom.
Boiling point: Low High
Examples: Methane (CH4), Sodium chloride (NaCl),
Occurs between: Two non-metals One metal and one non-metal
State at room temperature: Liquid or gaseous Solid
Polarity: Low High
Formation: A covalent bond is formed between two non-metals that have similar electronegativities. Neither atom is “strong” enough to attract electrons from the other. For stabilization, they share their electrons from outer molecular orbit with others An ionic bond is formed between a metal and a non-metal. Non-metals(-ve ion) are “stronger” than the metal(+ve ion) and can get electrons very easily from the metal. These two opposite ions attract each other and form the ionic bond.
Shape: Definite shape No definite shape
Melting point: low High

 

CH:8 ACIDS, BACE AND SALTS P:85-86

QUESTION No.5What is the effect of dilute HCI on the colours of the following?

Methyl orange, Phenolphthalein, Blue litmus

ANS:Dilute hydrochloric Acid (HCI) turns:

•                Blue litmus red

•                Methyl orange solution red

•           Phenolphthalein colourless

QUESTION No.6What is a base? Write down the names and formulae of four bases?
ANS:BASE:

A base is a chemical species that donates electrons or hydroxide ions or that accepts protons.

Base is compound whose molecule is made up of one or more hydroxyl groups (OH) attached to the atom of the metal.

Base formulae
1 Sodium hydroxide Na OH
2 Calcium hydroxide Ca(OH)2
3 Ammonium hydroxide NH4OH
4 Potassium hydroxide KOH
QUESTION No.7Mention the source of the following?

Citric acid, Tartaric acid, Acetic acid

ANS:
ACIDS SOURCE
1 Citric acid Lemon, Orange, lime, Grape fruits
2 Tartaric acid Grapes, Tamarind (imli)
3 Acetic acid Vinegar
QUESTION No.8What is the action of caustic soda on the colour of the following?

Red litmus, Phenolphthalein, Methyl orange

ANS:Caustic soda turns:

•                Red litmus blue

•                Methyl orange solution yellow

•                 colourless Phenolphthalein pink

 

CH: 9                                                      P:

 

Q No.3 ENCIRCLE THE CORRECT ANSWER IN THE FOLLOWING:

(i) Which one of the following is a good absorber of gases.

(a)     Coke (b)            Coal (c)         Charcoal                 (d) Lamp black

(ii)   In a candle flame partial combustion takes place in

(a)              the dark zone around the wick (b)     the yellow zone                                                           (c)    the pale blue zone                   (d)          small blue zone below the flame

(iii) Carbon exists in two crystalline forms as diamond and graphite. These are called

(a)     Isotopes (b)      Allotropes (d)            Non of these (c)      Isomers

(iv) In free state carbon occurs as

(b)    Coal gas (c)   Marble (d)      Diamond

(v)   Carbogen is a mixture of oxygen and carbon dioxide. Percentage of carbon dioxide in
this mixture is

(a)     30%             (b)            50% (c)           70% (d)          20%

Ans: (i-) (ii- ) (iii- )   (iv- ) (v- )

 

QUESTION No.4 GIVE SHORT ANSWERS:

Q No.iCarbon dioxide gas is present in air? Can you guess how it is formed?
ANS:Carbon dioxide gas is present in air. It is formed by burning of oil, respiration of the animals
&human and smoke of vehicles
Q No. iiWhat is catenation?
ANS:Carbon has the remarkable ability of forming linkages with other carbon atoms in long
chains. This is called catenation.
Q No.iiiWhich crystalline form of carbon is a good conductor of electricity?
ANS:Graphite is a form of carbon which is a good conductor of electricity.
Q No. ivHow carbon dioxide gas is obtained from molasses?
ANS:When molasses is heated at 37°C in the presence of enzymes, the carbon dioxide gas is
obtained.
Q No. vHow lamp is black prepared?
ANS:It is prepared by burning kerosene oil or vegetable oil with limited supply of air. The soot thus produced is deposited on a cool surface. It is known as lamp black.

 

QUESTION No.5Why carbon is called a unique element?
ANS:
QUESTION No.8Name the different non-crystalline forms of carbon?
ANS:Coal

Coke

Charcoal

lamp black

QUESTION No.9What is allotropy?
ANS: ALLOTROPY:If an element exists in more than one forms which posses different physical properties but identical chemical properties then these different forms are called allotropic forms of allotropes.

The property by virtue of which an element exists in m0re than 0ne forms is called allotropy

 

CH:11 LIQUID PRESSURE P: 110-111

 

Q No.3 ENCIRCLE THE CORRECT ANSWER IN THE FOLLOWING:

(i)The pressure at any point in a liquid depends upon

(a) Depth of the point                                                                                (b)        Area of the mouth of the vessel.                                                           (c)    Area of the bottom of the vessel                                                        (d) The thickness of the containing vessel.

(ii)   If we draw a horizontal line in a liquid the pressure would be

(a) Different at different parts of the line.                                                         (b)         Same on all of its parts.                                                                           ( c) Larger on its right side than on its left side.                                             (d)         Maximum at the center of the line.

(iii)    If we consider a point inside the liquid

(a)    The upward pressure on this point would be larger than the downward pressure.                                                                                     (b)    Pressure at this point from the right direction would be least.                                                       (c)          Pressure on its right side would be greater than the pressure on its left side.                                                                                                          (d)    Pressure on it would be the same from all directions.

(iv) In state of rest, the level of free surface of a liquid is

(a)    Higher at some places and lower at others.                                             (b)        Higher at the edge of the vessel.                                                            (c) Same every where.                                                                   (d)Lower at the edge of the vessel.

Ans: (i-a) (ii-b ) (iii-d )   (iv-c )

 

QUESTION No.4 GIVE SHORT ANSWERS:

Q No.iDefine pressure?
ANS:The perpendicular force acting on unit area of a surface is known as pressure.
Q No. iiIn what factors does the liquid pressure depend?
ANS:The liquid pressure depends on;

-The depth of vessel

-The surface area of containing vessel

 

QUESTION No.5State the characteristics of liquid pressure?
ANS:CHARACTERISTICS OF LIQUID PRESSURE:

             Characteristics of liquid pressure as follows:

1. Pressure exerted increase with the depth of liquid

2. Pressure at all points at equal depth is equal

3. Liquid exerts pressure on the wall of the container.

4. Pressure exerted is directly related to its density.

5. Pressure exerted on liquid is transmitted equally in all directions. (Pascal’s law)

CH:13 LIGHT P: 133-135

Q No.3 ENCIRCLE THE CORRECT ANSWER IN THE FOLLOWING:

(i)      A ray parallel to principal axis, after refraction from convex lens.

(a)    does not bend                                                                                          (b)   passes through principal focus                                                                    (c) passes through centre of curvature.                                                                     (d)    passes through the middle of principal focus and centre of curvature.

(ii)    The image formed by a concave lens is:

(a)     virtual                   (b)     real             (c)      inverted     (d)     larger

(iii)    Pupil is made smaller or larger by:

(a)     ciliary muscle      (b)     cornea       (c)      iris            . (d)      retina

(iv) The change in direction of light passing from one medium to another is called.

(a)     reflection    (b). refraction      (c)     dispersion     (d)     irregular reflection

(v)    The point through which ray of light passes without changing its path is the

(a) centre of curvature                                       (b)      principal axis                                               (c)    optical centre.       (d)                                 principal focus

 

Ans: (i-b) (ii- ) (iii- a ) (iv- b )   (v-c )

 

 

 

QUESTION No.4 GIVE SHORT ANSWERS:

Q No.iDescribe the paths of three rays passing through convex lens, which form image?
ANS: 

A ray parallel to the principal axis after refraction from lens passes through its principal focus.

A ray passing through the principal focus after refraction becomes parallel to the principal axis.

A ray passing through the optical centre of the lens goes straight without changing direction.

Q No. iiDefine lens?
ANS:Lens is a piece of transparent material. Its both sides are spherical.
Q No.iiiWhat is the structure of a concave lens?
ANS:A lens which is thick at the middle and thinner at the edges is called concave lens.

A lens which is thin at the middle and thick at the edges is called convex lens.

Q No. ivDefine focal length?
ANS:The distance between the optical center and the principal focus is known as focal length (f) of the lens.
Q No. vCan image be obtained on the screen by a concave lens?
ANS:No, it cannot image be obtained on the screen by a concave lens
Q No.vi       What is ray diagram?
ANS:The location and nature of image formed by a lens can be found very easily through a ray diagram.

In this process diagram is drawn geometrically and then image is traced from the diagram. In ray diagram, rays of light are represented by straight lines

Q No. viiHow is the focal length affected when the lens of eye becomes thicker?
ANS:The location and nature of image formed by a lens can be found very easily through a ray diagram.
Q No. viiiUpon what factors does the amount of light entering in a camera depend?
ANS:The amount of light entering in a camera depends upon the size of aperture.

 

CH:14 ELECTRICITY &MAGNETISM P: 146-148

 

Q No.3 ENCIRCLE THE CORRECT ANSWER IN THE FOLLOWING:

(i)             A lighted bulb consumes
               (a) electrons (b) positive charge(c) electrolyte (d) electrical energy
(ii)            The steam which runs electric generator is a source of
               (a) nuclear energy (b) wind energy(c) potential energy (d) mechanical energy
(iii)           Hydal power plant converts
               (a) mechanical energy into electrical energy(b) electrical energy into mechanical energy

(c) chemical energy into electrical energy

(d) heat energy into electrical energy

(iv)           A dry cell provides a voltage of
               (a) 1 volt (b) 1.5 volts (c) 2 volts (d) 3 volts
(v)            The unit of electric power is
               (a) ampere (b) volt (c) watt (d) kilowatt-hour

 

Ans: (i-d) (ii-d ) (iii- a ) (iv-b   ) (v- c)

 

QUESTION No.5Define and explain potential difference?
ANS:POTENTIAL DIFFERENCE:

The difference in electric potential between two points in an electric field; the work that has to be done in transferring unit positive charge from one point to the other. It is measured in volts. Its Symbol is U ΔVΔφ Abbreviation pd. It is also called voltage.

EXPLAINATION:

Potential difference is like an electrical pressure difference, which pushes the4 electrons in a conductor. A source of electricity such as cell or battery provides the potential difference across a conductor. The positive terminal of the battery is said to be at higher potential and the negative terminal at lower potential.

Potential difference is measured in volts.

QUESTION No.9How electricity is generated in a hydal power plant?
ANS:All streams and rivers flow downhill. Before the water flows down the hill, it has potential energy because of its height.

Hydro power systems convert this potential energy into kinetic energy in a turbine, which drives a generator to produce electricity. The greater the height and the more water there is flowing through the turbine, the more electricity can be generated.

The amount of electricity a system actually generates also depends on how efficiently it converts the power of the moving water into electrical power.

PROCESS:

Water is stored in a lake or reservoir at a height behind the dam. When water is allowed to fall from the height, it gains kinetic energy due to motion. Kinetic energy of the moving water flowing through the tunnels is used to turn the blades of turbines. These are attached to the lower end of the axil of the electric generator. The generator produces electricity which is supplied to the consumers through power stations.

Hydal power is low cost and produces no pollution.

QUESTION No.12What is electromagnetic induction? Explain it?
ANS:ELECTROMAGNETIC INDUCTION:
Production of an electric current by changing the magnetic field enclosed by an electrical circuit.

The most common use of it is in the electric generator.

EXPLAINATION:

Electromagnetic Induction was originally discovered in 1802 by Hans Orsted.

A decade later, Michael Faraday, observed that when a electric current runs through a wire, it creates a magnetic field around that wire.

Electromagnetic Induction Works on Faraday’s Laws of electromagnetic induction. Changing magnetic flux produces current in the wire. Similarly changing voltage produces magnetic field.

ACTIVITY:

Connect a long coil of wire in series with a galvanometer.
Take a bar magnet. Push it speedily into the coil pointing its north pole toward the coil. Keep observing the needle of galvanometer carefully while pushing in the magnet.

This phenomenon is called Electromagnetic Induction.

CH:16 GALAXIES & STARS P: 170-171

 

Q No.3 ENCIRCLE THE CORRECT ANSWER IN THE FOLLOWING:

  • Clouds of dust and gases in space are:

(a)Supernova              (b) Nebula                                                   (c) Constellation           (d) Coma

(ii)Our solar system is a part of galaxy

(a)Ursa Major       (b) Andromeda(c) Milky Way        (d) Orion

(iii) The external temperature of the outer surface of the sun

(a)3000 C           (b) 6000 C(c)       15000 C         (d) 50000 C

(iv) The fields of gases and dust around the nucleus of the comet are:

(a) Core               (b) Coma(c)         Black         (d) Nebula

(v) The planets revolving around the sun between Mars and Jupiter are:

(a) Comets·             (b) Meteoroids(c) Asteroids (d) Meteorites

Ans: (i-b) (ii-c )   (iii-b ) (iv-b   ) (v-c )

 

QUESTION No.4 GIVE SHORT ANSWERS:

Q No.iWhat is meant by big bang?
ANS:The night sky presents the viewer with a picture of a calm and unchanging Universe. So, the 1929 discovery by Edwin Hubble that the Universe is in fact expanding at enormous speed was revolutionary.

According to this theory, about 14 billion years ago, when the entire Universe was contained in a single point in space. The Universe must have been born in this single violent event which came to be known as the “Big Bang.”

Q No. iiWhat is meant by nebula?
ANS:NEBULA:

A nebula (Latin) is an interstellar cloud in outer space that is made up of dust, hydrogen and helium gas, and plasma.

It is formed when portions of the interstellar medium collapse and clump together due to the gravitational attraction of the particles.

Q No.iiiWhat is meant by constellation?
ANS:CONSTELLATION:

A group of stars forming a pattern that is traditionally named after its apparent form.

There are 88 groups of stars as seen from the earth.      For example: Leo, Great Bear etc.

Q No. ivWhat is black hole?
ANS:BLACK HOLE:

An area of space-time with a gravitational field so intense that its escape velocity exceeds the speed of light.

FORMATION:

If the mass of the core of star is three times bigger that mass of the Sun, then the core of star is contracts in such a way that too much density comes on one point. It is called black hole.

Q No. vWhat is meant by comets?
ANS:COMETS:

A comet that is not near the Sun consists only of a solid core of frozen water, frozen gases, and dust.

When a comet comes close to the Sun, it releases a gaseous tail (coma).

 

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