Grade 8 Science Notes (2016-17) PDF

GRADE 8 SCIENCE NOTES REVISED 2016 – 17 3. Inter neurons CHAPTER # 1 HUMAN ORGAN SYSTEM These are present in CNS. They form a link between...

GRADE 8 SCIENCE NOTES REVISED 2016 – 17 3. Inter neurons CHAPTER # 1 HUMAN ORGAN SYSTEM These are present in CNS. They form a link between sensory and motor neurons. 1) Define nervous system 11) Write the names of main parts of the followings The organ system in our body that carries messages from 1. Forebrain one part of the body to another part and coordinates It consists of three main parts body functions is called nervous system. I. Cerebrum 2) What is CNS? II. Thalamus CNS means central nervous system that includes brain III. Hypothalamus and spinal cord. 2. Hindbrain 3) What is PNS? It consists of three main parts PNS means peripheral nervous system that includes a I. Cerebellum network of nerves connecting the central system to whole II. Pons body. III. Medulla oblongata 4) Define Neuron or Nerve Cell. 3. Neuron Neuron or nerve cell is the basic structure and functional It consists of three main parts unit of the nervous system. All parts of the nervous I. Cell body system are made up of neurons. II. Dendrites 5) Define Nerve impulses. III. Axon Neurons carry messages in the form of electro-chemical 4. Nephron waves called nerve impulses. It consists of two main parts 6) Define cell body. I. Renal corpuscle The part of neuron containing nucleus and most of the II. Renal tubule cytoplasm is called cell body. 12) Write the function of the followings 7) Define Dendrites. 1. Forebrain A fine projection of the cell body that receives messages is It is the largest part of the brain. It consists of three main called dendrites. parts 8) What is Axon? I. Cerebrum A long projection of the cell body that conducts messages II. Thalamus away from the cell body is called axon. III. Hypothalamus 9) Define Nerve. Cerebrum is the topmost and the largest part of the brain. It is an enclosed, cable like bundle of axons present side It controls many actions like thinking, feelings, emotions, by side in a common sheath. Nerve conveys messages seeing, hearing, perceptions, memory, speech, decision carried by the individual neurons from one body part to making, etc. another. Inside cerebrum there is a small structure called 10) How many types of neurons are there? thalamus. It controls many sensory functions. There are three types of neurons on the basis of Hypothalamus lies at the base of thalamus. It controls functions. body temperature, hunger and thirst. I. Sensory neurons 2. Hindbrain II. Motor neurons It consists of three main parts III. Inter neurons I. Cerebellum 1. Sensory neurons II. Pons It carries nerve impulses from sense organs (ears, eyes, III. Medulla oblongata skin, tongue, nose etc) to the central nervous system Cerebellum lies under the back part of cerebrum. It acts (CNS). as a controller for maintaining balance and accurate 2. Motor Neurons movements. It carries nerve impulses from central nervous system Pons is oval structure and present beneath the midbrain. (CNS) to effectors (muscles and glands), i.e. the parts It controls many function like sleeping, swallowing, which respond. equilibrium and taste etc. GOVT. ELEMENTARY SCHOOL CUSTOM ACADEMY WALTON CANTT LAHORE Page 1 of 20  GRADE 8 SCIENCE NOTES REVISED 2016 – 17 Medulla oblongata is connected with the spinal cord. It nervous system. All parts sheath. Nerve conveys controls heartbeat, breathing and digestion etc. it also of the nervous system are messages carried by the keeps working when rest of brain goes to sleep. made up of neurons. individual neurons from one body part to another. 3. Neuron or Nerve Cell Neuron or nerve cell is the basic structure and Voluntary actions Involuntary actions functional unit of the nervous system. All parts of the The body actions which are The body actions which are nervous system are made up of neurons. It consists of performed without thinking performed under conscious three main parts over them under conscious control. These actions are control are called I. Cell body done after thinking. involuntary actions. e.g. speaking, eating, II. Dendrites e.g. Heartbeat, blood reading, walking, running, III. Axon circulation, blinking of eyes etc etc. I. Cell body Kidneys Lungs The part of neuron containing nucleus and most of the cytoplasm is called cell body. Human body has two dark Lungs are present in the brown, bean shaped kidneys II. Dendrites thorax cavity in pair form. in the abdominal region. The Lungs make oxygenated A fine projection of the cell body that receives messages is main function is removing blood and remove carbon called dendrites. waste material from the dioxide from the blood. body in the form of urine. III. Axon Lithotripsy Dialysis A long projection of the cell body that conducts messages It is the bombardment of away from the cell body is called axon. Terminal ends of shock waves on the stones the axons transmit the messages to the next cells. from outsides. Shock waves Clearing of blood by artificial break the stones into small methods is called dialysis. It pieces which are passed out is done by dialyzer. of the body in the form of urine. 15) Explain central nervous system. CNS acts as a control Centre of the whole nervous system. It contains brain and spinal cord. Brain Human brain is enclosed in a bony skull called cranium. It 4. Nephron divided into following parts. It is the functional unit of kidneys. It consists of two main 1. Forebrain parts It is the largest part of the brain. It consists of three main I. Renal corpuscle parts II. Renal tubule I. Cerebrum These are the tubules where urine is formed. There are II. Thalamus over one million nephrons in each kidney. III. Hypothalamus 13) Skin is considered as excretory organ. Why? Cerebrum is the topmost and the largest part of the brain. Because some extra salts are also removed through skin It controls many actions like thinking, feelings, emotions, during perspiration. seeing, hearing, perceptions, memory, speech, decision 14) Differentiate between making, etc. Receptors Effectors Inside cerebrum there is a small structure called The special organ tissue The parts respond after thalamus. It controls many sensory functions. which detect any change receiving nerve impulses Hypothalamus lies at the base of thalamus. It controls in environment is called through motor neurons is receptors. called effectors. body temperature, hunger and thirst. Neuron Nerve 2. Midbrain Neuron or nerve cell is the It is an enclosed cable like It is a small part of the brain that is present below basic structure and bundle of axons present cerebrum. It receives information from sense organs and functional unit of the side by side in a common sends messages to concerned part. GOVT. ELEMENTARY SCHOOL CUSTOM ACADEMY WALTON CANTT LAHORE Page 2 of 20  GRADE 8 SCIENCE NOTES REVISED 2016 – 17 3. Hindbrain 2. Renal medulla and renal pyramids It consists of three main parts Renal medulla is the middle regions which is divided into I. Cerebellum conical masses called renal pyramids. II. Pons 3. Renal pelvis III. Medulla oblongata It is the inner area where urine is drained. The urine from Cerebellum lies under the back part of cerebrum. It acts renal pelvis moves into ureter. as a controller for maintaining balance and accurate 19) Describe structure of nephron movements. It is the functional unit of kidneys. It consists of two main Pons is oval structure and present beneath the midbrain. parts It controls many function like sleeping, swallowing, I. Renal corpuscle equilibrium and taste etc. II. Renal tubule These are the tubules where urine is formed. There are Medulla oblongata is connected with the spinal cord. It over one million nephrons in each kidney. controls heartbeat, breathing and digestion etc. it also keeps working when rest of brain goes to sleep. 4. Spinal Cord It is an extension of medulla oblongata. It runs backwards inside the backbone up to its lower end. It creates a link between brain and different body parts. It also controls some reflex actions and some other involuntary actions. 16) Describe peripheral nervous system (PNS). PNS includes a network of nerves connecting the central system to whole body. The nerves which arise from brain are called cranial Renal corpuscle nerves. The nerves which arise from spinal cord are called It is the first part of nephron. It consists of two structures, spinal nerves. There are 12 pairs of cranial nerves and 31 i.e. glomerulus and Bowman’s capsule. pairs of spinal nerves in human body. Glomerulus is a tuft of blood capillaries formed by the 17) Describe the main parts of excretory system in man. division of small arteries. It consists of one pair of kidneys and associated structure. Bowman’s capsules is a cup shaped structure enclosing i.e. two ureter, a urinary bladder and urethra. glomerulus. 1. Kidneys Renal tubule Human body has two dark brown bean shaped kidneys in the It is start after bowman’s capsules. The first coiled part of abdominal region. The main function is removing waste renal tubule is called proximal tubule. The next part is U- material from the body in the form of urine. The outer surface shaped and is called Loop of Henle. The last part of the of kidney is convex while the inner surface is concave. renal tubule is again coiled called distal tubule. 2. Ureter 20) Define reflex action. A tube which arises from each kidney and enters in An immediate and involuntary response to a stimulus is urinary bladder is called ureter. called reflex action. 3. Urinary bladder Ureter transports urine from kidneys to urinary bladder. Quick pulling of hand just after touching the hot object is Urinary bladder is a muscular sac which collects urine a common example of reflex action. from both ureters. Explanation 4. Urethra When we touch hot object a nerve impulse is created in A fine tube through which urine is released from urinary skin. It is carried by the sensory neuron to the spinal cord. bladder to the outside is called urethra. The inter neuron transmit the impulse to motor neuron. They carried the impulse to muscles. The pathway of 18) Write a note on internal structure of kidneys nerve impulse that complete a reflex action is called Each kidney is divided into three regions reflex arc. It consists of receptor, a sensory neuron, an 1. Renal cortex inter neuron, a motor neuron and effectors. It is the outer most region of kidney GOVT. ELEMENTARY SCHOOL CUSTOM ACADEMY WALTON CANTT LAHORE Page 3 of 20  GRADE 8 SCIENCE NOTES REVISED 2016 – 17 21) Define Reflex arc. 3) What is gene? The inter neuron transmit the impulse to motor neuron. The basic physical and functional unit of heredity is called They carried the impulse to muscles. The pathway of gene. Genes act as instructions to make molecules called nerve impulse that complete a reflex action is called proteins. Gene occur in pairs. Every hereditary character reflex arc. It consists of receptor, a sensory neuron, an in an organism (tallness, eye colour) is controlled by a pair inter neuron, a motor neuron and effectors. of genes. Genes are the sections of DNA molecule and are 22) What is renal failure? located on chromosomes It is a complete or partial failure of kidneys to work. The 4) Define heredity main cause of renal failure are During reproduction, living things pass on their I. long term infection characteristics to their offspring. This process is called II. Diabetes mellitus heredity e.g. colour of eye, skin colour, hair colour etc III. Hypertension 5) What are haploid cells? 23) Define diabetes When an organism forms gametes (sperms or eggs) by Diabetes mellitus is disease in which sugar level increases meiosis, the number of chromosomes is reduced to half in in the blood. the gametes, is called haploid cell. 24) What is Hypertension? 6) Define cell division It is a state of high blood pressure in the body. It is a process by which a cell divides into two daughter cells. 25) What is dialyzer? Clearing of blood by artificial methods is called dialysis. It 7) What are parent cell and daughter cell? is done by a machine called dialyzer. During cell division the cell which divides is called Parent Cell and the cell which is produced as a result of cell 26) What is kidney transplant? division is called Daughter Cell. In this method a kidney donated by some healthy person is grafted in the body of the patient. The donar of kidney 8) What are chromatids? may be blood relative or any other close relative. A typical chromosome consists of two arms called chromatids, which are attached to the same part called 27) Name any two waste materials produced by the centromere. human body 1: Urine 2: Feces 28) How stones are formed in the kidney and how can these be removed? Sometimes kidneys cannot work properly to remove salt from blood. In such situation, the salts gather in kidneys 9) Difference between Mitosis and Meiosis and form stones. Mitosis Meiosis Stones can be removed in three ways During mitosis, two During meiosis, four daughter cells are daughter cells are I. By drinking water produced from the parent produced from parent II. Lithotripsy cell. III. shockwaves The number of The number of chromosomes in the chromosomes in the daughter cells remains the daughter cells is reduced CHAPTER # 2 CELL DIVISION same as in parent cell to half as compared to parent cell Mitosis occurs in general Meiosis occurs to produce 1) Name two inheritable characters. body cells gametes in animal or Eye colour spores in plants Skin colour Only one division takes Two division take place in 2) Name two non-inheritable characters. place in mitosis meiosis. I. Loss of any part of body does not transferred to children. 10) Name the cells produced by meiosis in plants and II. Some diseases like malaria, kidney-stone etc does animals not transferred to children Plant: Spores Animals: Gametes GOVT. ELEMENTARY SCHOOL CUSTOM ACADEMY WALTON CANTT LAHORE Page 4 of 20  GRADE 8 SCIENCE NOTES REVISED 2016 – 17 11) Define heredity and describe its importance in 3) Briefly describe gene therapy transferring characteristics from parents to offspring. It is an advanced biotechnological technique which is used During reproduction, living things pass on their to cure genetic and acquired diseases like cancer and characteristics to their offspring. This process is called AIDS. In the process, defective genes are supplemented or heredity for examples replaced by normal genes. I. Colour of eye 4) Name two life saving products of biotechnology. II. Skin colour Insuline: it is used for diabetes III. Hair colour Vaccines: it is used against many infection disease. IV. Free or attached earlobes 5) What is DNA replication? V. Height The process by which DNA makes its copy is called DNA VI. Intelligence replication. 12) Write a note on DNA 6) What is genetic engineering? DNA means Deoxyribonucleic acid. As different sections of It is an advanced technique of biotechnology in which DNA are a set of information for the development of scientist select and isolate the useful gene from one different characters in an organism. So, DNA is called organism (donor organism) and insert it into another hereditary material. organism usually bacterium. 13) What is Watson and crick Model of DNA? 7) What is transgenic organism? Each DNA molecule is made of thousands of small units The organism that contains a foreign gene in its cells is called nucleotides. There are four types of nucleotides in called transgenic organism. DNA. 8) Why do scientists use bacteria in genetic I. Adenine (A) nucleotides engineering? II. Thymine (T) nucleotides Bacterial cell is very simple and easy to handle for the III. Cytosine (C) nucleotides scientists. It is easy for the scientists to isolate plasmid IV. Guanine (G) nucleotides from a bacterial cell and attach a gene with it. Another According to them, DNA molecule consists of two stands reason is its fast rate of reproduction. formed of nucleotides. These two are linked with each 9) What is genetic modification? other by cross bands like a ladder. The change in the genes of organism using biotechnology 14) Write a note on Chromosomes. techniques is called genetic modification. The nucleus of the cell contains thread like structures 10) What is GMO? called chromosomes. Chromosomes are composed of The organism whose genes are modified called genetically DNA and proteins. They appear as distinct structures modified organism (GMO). GMO are also used to prepare found in the nucleus of a cell. They appear as distinct useful and life saving products such as insulin and structures only during cell division. vaccines etc. A typical chromosome consists of two arms called 11) What is insulin? chromatids, which are attached to the same part called Insulin is a human protein. In human body it is produced centromere. by pancreas. It controls the glucose level in blood. CHAPTER # 3 BIOTECHNOLOGY 12) What is vaccine? Vaccine is a material which contains weakened or killed pathogens (disease causing germs) and is used to produce 1) What is biotechnology? immunity against a disease. The technology in which living things are used in different 13) How vaccine works? ways to help and benefit human beings is called When a vaccine is given to human body, the blood cells in biotechnology. the body take the dead or weak pathogens as real ones 2) What is genetic testing? and prepare antibodies against them. These antibodies It is one of the latest biotechnological techniques used for remain in blood when any real pathogens enters the genetic diagnosis of inherited diseases. It involves the body, the already present antibodies kill it immediately direct examination of DNA molecule. It is also used to and the body becomes protected from disease. determine a child’s paternity or a person’s ancestry. GOVT. ELEMENTARY SCHOOL CUSTOM ACADEMY WALTON CANTT LAHORE Page 5 of 20  GRADE 8 SCIENCE NOTES REVISED 2016 – 17 14) What is diabetes mellitus? III. Oxides of nitrogen If pancreas does not produce the required amount of IV. Water vapours insulin, the level of glucose in blood rises. This condition is 3) Name the acids which are present in acid rain. known as diabetes mellitus. I. Sulphuric acid 15) Differentiate between herbicides and pesticides? II. Nitric acid Herbicides are weed killing chemicals and pesticides are 4) Why ozone layer is important? insect killing chemicals which are used to eliminate the Ozone layer prevents to enter ultraviolet (UV) rays to the crop enemies (weed and insects) such chemicals also earth. These rays are harmful for life. cause damage to the crop plants. 5) 3R strategies stand for what? 16) Which major crops have been modified? 3R stands for “Reduce-Reuse-Recycle” Maize (corn), wheat, rice, conola, potato, soybean, 6) Write down the names of products which are cotton, etc recycled? 17) What are trying to produce Pakistani scientist? I. Glass piece They are trying to produce wheat higher production of II. Aluminium iron in the flour. This may help to overcome iron III. Steels cans deficiency in food. IV. Copper wires 18) Which insects damage the wheat crop? How can V. Paper solve this problem? 7) Name common method used for solid waste Insects called aphids damage the wheat crop. management. This problem can solved by producing aphid resistant I. Landfill varieties using genetic engineering techniques. II. Incineration III. Recycling 19) Describe the use of vitamin B12. Vitamin B12 widely used as food addictive and in some 8) How does ozone depletion contribute towards global medicines. It is produced in high yielding cultures of warming? bacteria. UV rays can enter into the earth so the temperature of the earth is increasing and earth globe is getting warmer. 20) Name some biotechnology products and tell about This is called global warming. their uses. 1. Insulin: Useful for diabetes. 9) Sulphur dioxide is an important. From where does it 2. Vaccine: Used against many infections disease. enter the atmosphere? 3. Beta Endorphin: A pain killer drug Sulphur dioxide is produced by burning of coal or oil in 4. Interferon: Anti-viral proteins. factories. Smoke released from thermal power stations usually contain Sulphur dioxide. 21) Define cloning. 10) Describe the adverse effect of carbon monoxide on It is also amongst the latest biotechnological techniques human organ system. used for treating various diseases. It can also be used for I. It causes headache. the production of animal organs. II. It causes brain damage and respiratory problems. III. When CO reaches our blood, it gets bonded with CHAPTER # 4 POLLUTANTS & THEIR hemoglobin and reduced its oxygen carrying EFFECTIS ON ENVIRONMENT capacity. 11) What is greenhouse effect? When sunlight falls on the earth, a small part of it is 1) What are the main air pollutants? absorbed by the earth and is converted to heat energy. A I. Carbon monoxide (CO) part of this heat energy is reflected back to the atmosphere by the earth. Some gases present in the II. Sulphur dioxide (SO2) atmosphere e.g, III. Oxides of nitrogen (NO & NO2) I. Carbon monoxide (CO) IV. Chlorofluoro carbons (CFCs) II. Sulphur dioxide (SO2) 2) Name greenhouse gases. I. Carbon dioxide III. Oxides of nitrogen (NO & NO2) II. Methane GOVT. ELEMENTARY SCHOOL CUSTOM ACADEMY WALTON CANTT LAHORE Page 6 of 20  GRADE 8 SCIENCE NOTES REVISED 2016 – 17 These gases trap a part of the heat reflected by the earth I. By keeping the environment clean causing increase in the atmospheric temperature. These II. They can make awareness among people to gases are called greenhouse gases and the phenomenon reduce harmful human activities. is called greenhouse effect. III. By planting new plants. 12) What is global warming? Write its effect on earth. 2. Farmers Due to greenhouse effect, the earth’s globe is getting I. By planting more and more trees warmer. This is called global warming. II. By keeping fields greens throughout the years. Effects III. By making artificial forests to reduce pollution. I. Ice in the Polar Regions and at the mountains 3. Factory owners melts, sea level rise and results in flood. I. Factory wastes must be treated before disposing II. Climate of the World is changing. them. 13) What is ozone depletion? II. Waste should be neutralizes before entering in A layer in the upper atmosphere is called ozone (O3) layer. the air. It prevents to enter ultraviolet (UV) rays to the earth. III. Factories should be shifted far from urban areas. These rays are harmful for life. 4. Scientists I. Scientist must recycle chemicals and solids Chlorofluorocarbons (CFCs) react with ozone layer and II. Less use of resources must be done. cause thinning of ozone layer when leaked form air III. Wastage of resources must be stopped and conditioners etc. Hence depletion is takes place and called checked. ozone depletion. 17) What is deforestation? Explain its effect on wild life. Effects Destruction of forests due to human activities is called I. UV rays can enter into the earth and causes serious deforestation. diseases like skin cancer, eye problems. II. The temperature is increasing. Effects I. It destroys habitats of wild life. 14) What is acid rain? II. Extinction rate of wild life is increased. Oxides of Sulphur and nitrogen (SO2 , NO, NO2) react with water vapours in the air and forms acids which make the 18) What types of climatic changes can appear by rain water acidic. deforestation? Effects I. Due to deforestation, the rate of evaporation is I. Acid rain kills the aquatic life in rivers and ponds. reduced which results in less rain. II. Acid rain destroys the leaves of trees. II. Greenhouse effect is increased which results in III. Acid rain destroys the metals and stones in buildings global warming. IV. Crops do not grow in acidic soil. 19) What is recycling? 15) Point out the sources of air pollutants you find in In this method, plastic items, glass pieces, aluminum, your locality and suggest ways to reduce the steels cans, copper wires, etc are collected separately pollution. cleaned, melted and moulded into new products. In this Sources of pollutants way, they are used again and again to reduce pollution. I. Vehicle’s smoke 20) What should we do to adopt 3R strategies for II. Industrial smoke conservation of resources? III. CFC in aerosol spray I. Reduce IV. Rotting vegetation By reducing the use of non-biodegradable objects and Methods to reduce pollution the resources that are used in their manufacture I. Public transport should be used instead of personal should be conserved. cars. II. Reuse II. Sulphur and lead free fuel should be used in vehicles Secondly, reuse of non-biodegradable objects again III. Factories should be shifted away from urban areas. and again instead of throwing them after first use. IV. CFC free products should be used. III. Recycle V. Deforestation should be avoided. Thirdly, plastic items, glass pieces, aluminum, steels cans, copper wires, etc are collected separately 16) Suggest what can following communities do to cleaned, melted and moulded into new products. reduce air pollution. 1. Students GOVT. ELEMENTARY SCHOOL CUSTOM ACADEMY WALTON CANTT LAHORE Page 7 of 20  GRADE 8 SCIENCE NOTES REVISED 2016 – 17 CHAPTER # 5 CHEMICAL REACTION 7) When coal burns it leaves ash behind. Ash so produced is lighter than the coal which has burnt. Justify the decrease in mass in the light of law of 1) Define a chemical reaction. conservation of mass. The process in which a substance changes into entirely The decrease in mass of coal is due to the formation of new substance with different chemical composition and gaseous products i.e. 𝐶𝑂2 that escape into air and only properties is called chemical reaction. lighter ash is left behind. So the total mass of reactants 2) What are reactants? remains equal to the products. Substances which take part in a chemical reaction are 𝐶 + 𝑂2 → 𝐶𝑂2 + 𝐴𝑠ℎ called reactants. A + B C + D 8) Give two examples of following chemical reactions. In above reaction A & B are reactants. Addition reaction Decomposition reaction 3) What are products? Substances which are formed in a chemical reaction are 2𝐻2 + 𝑂2 → 2𝐻2 𝑂 2𝐾𝐶𝑙𝑂3 → 2𝐾𝐶𝑙 + 3𝑂2 called products. 𝑁2 + 3𝐻2 → 2𝑁𝐻3 𝐶𝑎𝐶𝑂3 → 𝐶𝑎𝑂 + 𝐶𝑂2 A + B C + D Exothermic reaction Endothermic reaction In above reaction C & D are products. 𝐶 + 𝑂2 → 𝐶𝑂2 𝐶𝑎𝐶𝑂3 + 𝐻𝑒𝑎𝑡 → 𝐶𝑎𝑂 4) What is a chemical equation? 𝐶𝐻4 + 𝑂2 → 𝐶𝑂2 + 𝐻2 𝑂 + 𝐻𝑒𝑎𝑡 + 𝐶𝑂2 The representation of chemical reaction in terms of symbols, 𝐹𝑒 + 𝑆 → 𝐹𝑒𝑆 + 𝐻𝑒𝑎𝑡 𝐻2 + 𝐼2 + 𝐻𝑒𝑎𝑡 → 2𝐻𝐼 formulae and signs are called chemical equation. The 𝑁2 + 𝑂2 + 𝐻𝑒𝑎𝑡 → 2𝑁𝑂2 reactants is written on left side while products on right sides. A + B C + D 9) Describe application of chemical reactions. 5) State law of conservation of mass I. Heat produced during burning of fuel is used to cook During a chemical reaction the total mass of the reactants food. is equal to the total mass of products. II. Energy produced during respiration is used to 6) Differentiate between perform all the function of the body. ADDITION REACTION DECOMPOSITION REACTION III. Useful fermentation products e.g. yogurt and backing The chemical combination A chemical reaction during product are also application of chemical reaction. of two or more substance a compound splits up into IV. During photosynthesis in plants carbon dioxide and to form one compound is two or more simple water react to produce glucose in the presence of called addition reaction. substances are called sunlight and chlorophyll. decomposition reaction. 2𝐻2 + 𝑂2 → 2𝐻2 𝑂 2𝐾𝐶𝑙𝑂3 → 2𝐾𝐶𝑙 + 3𝑂2 𝐶𝑂2 + 𝐻2 𝑂 𝑠𝑢𝑛𝑙𝑖𝑔ℎ𝑡 𝐶6 𝐻12 𝑂6 + 𝑂2 𝑁2 + 3𝐻2 → 2𝑁𝐻3 𝐶𝑎𝐶𝑂3 → 𝐶𝑎𝑂 + 𝐶𝑂2 V. During respiration the oxygen of air reacts with food Balance Chemical Equation Unbalance Chemical Equation (glucose) to produce, carbon dioxide and water in the The chemical equation in The chemical equation in cell of living organisms. which the number of atoms which the number of 𝐶6 𝐻12 𝑂6 + 6𝑂2 → 6𝐶𝑂2 + 6𝐻2 𝑂 + 𝐸𝑛𝑒𝑟𝑔𝑦 of each element on both atoms of each element on 10) What is fermentation reaction? sides of equation i.e. on both sides of equation i.e. Conversion of milk into yogurt and formation of baking reactants & Product side on reactants & Product products involve the chemical changes carried by are equal is called balanced side are not equal is called microorganisms. Such reaction are called Fermentation chemical equation. unbalanced chemical 11) How chemical equation is written. 𝐻𝐶𝑙 + 𝑁𝑎𝑂𝐻 → 𝑁𝑎𝐶𝑙 + 𝐻2 𝑂 equation. The reactants and products are separated by arrow. 𝐻2 + 𝐶𝑙2 → 𝐻𝐶𝑙 Reactants on left while products are written of right hand Exothermic reaction Endothermic reaction side of arrow. The arrow is directed toward products. That reaction in which heat That reaction in which 12) Write down the rules for balancing a chem. is given out is called heat is absorbed are called Equation. exothermic reaction. endothermic reactions. I. Firstly count the number of atoms of each element on Burning is common Thermal decomposition of both side of the arrow. example of exothermic calcium carbonate is an reaction. endothermic reaction II. Only balance one element at a time. 𝐶 + 𝑂2 → 𝐶𝑂2 𝐶𝑎𝐶𝑂3 + 𝐻𝑒𝑎𝑡 → 𝐶𝑎𝑂 𝐶𝐻4 + 𝑂2 → 𝐶𝑂2 + 𝐻2 𝑂 + 𝐻𝑒𝑎𝑡 + 𝐶𝑂2 GOVT. ELEMENTARY SCHOOL CUSTOM ACADEMY WALTON CANTT LAHORE Page 8 of 20  GRADE 8 SCIENCE NOTES REVISED 2016 – 17 III. Multiply the symbol or formula with suitable integers III. Strong acids are corrosive liquids. They burn skin and (2,3,4,5 etc) on that side of equation where the destroy fabrics and animal tissues. number of atom of a particular element is less and try IV. Aqueous solutions of acids are good conductors of to balance this element on both sides of equation. electricity. IV. Starts multiply with smaller number. V. Acids react with reactive metals (Mg, Zn) to form salt and evolve hydrogen. V. Repeat the process for all the elements one by one. VI. Balance the diatomic molecules like 𝐻2 , 𝑁2 , 𝑂2 at the 4) Mention the uses of salts in industries end I. Sodium chloride (NaCl) is used for the manufacture of chlorine, hydrogen chloride, caustic soda, washing Note: Solve all examples from Text Book soda and sodium hydrogen carbonate. II. Sodium carbonate is used for softening hard water 13) Describe the importance of exothermic reaction in and for the manufacture of glass and soap. everyday life. III. Potassium nitrite is used for the preparation of gun I. They are widely used to fulfill our needs of heat powder, fireworks and fertilizer. energy for various purposes. IV. Copper sulphate is used as fungicide in calico printing II. The heat released during burning of fuel at our homes and in electroplating. is used for cooking food and to warm our rooms. 5) Name the salt which reduces acidity in our stomach. III. Heat produced during digestion of food in our body Sodium chloride (NaCl) keeps us warm and alive. 6) What happens when a salt like copper sulphate IV. Heat produced by Burning of fuel in thermal power reacts with water? station is used in generating electricity. Sulphuric acid and copper oxide (CuO) is formed 14) Give two examples of chemical reaction from 𝐶𝑢𝑆𝑂4 + 𝐻2 𝑂 → 𝐶𝑢𝑂 + 𝐻2 𝑆𝑂4 everyday life which are essential for life. 7) Is soda water acidic or basic? Photosynthesis and respiration are the two essential chemical reactions for our life. Soda water is acidic I. During photosynthesis in plants carbon dioxide and 8) Which alkali is commonly used to open a drain? water react to produce glucose in the presence of Potassium carbonate strong alkaline solution is used to sunlight and chlorophyll. open a drain. 𝐶𝑂2 + 𝐻2 𝑂 𝑠𝑢𝑛𝑙𝑖𝑔ℎ𝑡 𝐶6 𝐻12 𝑂6 + 𝑂2 9) Write down the reaction of ammonia and water. II. During respiration the oxygen of air reacts with food 𝑁𝐻3 + 𝐻2 𝑂 𝑁𝐻4 𝑂𝐻 (glucose) to produce, carbon dioxide and water in the Ammonia Water Ammonium Hydroxide cell of living organisms. 10) How litmus solution is prepared? 𝐶6 𝐻12 𝑂6 + 6𝑂2 → 6𝐶𝑂2 + 6𝐻2 𝑂 + 𝐸𝑛𝑒𝑟𝑔𝑦 Litmus solution is prepared by dissolving red cabbage juice or turmeric powder. CHAPTER # 6 ACIDS, BASES / 11) What is the effect of dilute HCl on the colour of ALKALIES & SALTS following? Indicator Colour in dil HCl 1) Define an acid. Methyl orange Red Acids can be defined as the compounds which produce Phenolphthalein Colourless hydrogen ions (H+) in their aqueous solution. Acids have Blue litmus Red sour taste. 12) What is base? Write down the names and formulae 2) Name some mineral acids. of four bases. Hydrochloric acid 𝐻𝐶𝑙 Bases are the compounds that produce hydroxide ions Nitric acid 𝐻𝑁𝑂3 (OH-) in their aqueous solution. Sulphuric acid 𝐻2 𝑆𝑂4 Examples: Phosphoric acid 𝐻3 𝑃𝑂4 Sodium hydroxide NaOH 3) State the properties of Acids Potassium hydroxide KOH I. All acids have sour taste Calcium hydroxide Ca(OH)2 II. All acids turn blue litmus solution and methyl orange Ammonium hydroxide NH4OH solution Red. Magnesium hydroxide Mg(OH)2 GOVT. ELEMENTARY SCHOOL CUSTOM ACADEMY WALTON CANTT LAHORE Page 9 of 20  GRADE 8 SCIENCE NOTES REVISED 2016 – 17 13) State the properties of Bases iii. Copper oxide reacts with dil. Sulphuric acid I. Aqueous solution of a base has a soapy touch Copper salt and water are produced II. All bases turn Red litmus blue, colourless 𝐶𝑢𝑂 + 𝐻2 𝑆𝑂4 → 𝐶𝑢𝑆𝑂2 + 𝐻2 𝑂 phenolphthalein pink and methyl orange yellow. iv. Sodium reacts with chlorine III. Aqueous solutions of bases are good conductors of Sodium salt are produced which also used in cooking. electricity. 2𝑁𝑎 + 𝐶𝑙2 → 2𝑁𝑎𝐶𝑙 IV. Bases react with acids to form salts and water. This reaction is called neutralization reaction. 18) Why the aqueous solutions of NaHCO3 and Na2CO3 are basic in nature? 𝑯𝑪𝒍 + 𝑵𝒂𝑶𝑯 → 𝑵𝒂𝑪𝒍 + 𝑯𝟐 𝑶 Because a strong base is formed 14) What is the action of caustic soda on the colour of following? 𝑁𝑎2 𝐶𝑂3 + 2𝐻2 𝑂 → 2𝑁𝑎𝑂𝐻 + 𝐻2 𝐶𝑂3 Indicator Colour after action of Caustic soda 19) How does the soil become acidic? Red litmus Blue Acid rain turns the soil acidic Phenolphthalein Pink 20) Sulphuric acid 𝑯𝟐 𝑺𝑶𝟒 molecule can give two Methyl orange Yellow protons in water whereas hydrochloric acid 𝑯𝑪𝒍 15) Mention the sources of the following. molecule can give only one proton. Does that mean sulphuric acid is twice as strong an acid as HCl? Name Source Yes, 𝐻2 𝑆𝑂4 is twice as strong an acid as 𝐻𝐶𝑙 Citric acid Citrus fruits Tartaric acid Tamarind, Grapes 21) Indicate in front of each salt the acid and the base which have been used to produce them. Acetic acid Vinegar Name of salt Acid Base Formic Acid Ant’s string Acetic acid Calcium Hydroxide Oxalic acid Tomatoes Calcium acetate 𝐶𝐻3 𝐶𝑂𝑂𝐻 𝐶𝑎(𝑂𝐻)2 Lactic acid Curd Potassium Malic Acid Apples Potassium Sulphuric Acid Hydroxide Stearic acid Fats hydrogen sulphate 𝐻2 𝑆𝑂4 𝐾𝑂𝐻 Magnesium Nitric Acid 16) Describe how salts are useful for the human body Magnesium nitrite Hydroxide 𝐻𝑁𝑂3 𝑀𝑔(𝑂𝐻)2 I. Sodium and potassium salts are needed for the proper functioning of muscles and the nervous Ammonium Ammonium Oxalic Acid Hydroxide system. oxalate 𝐶2 𝐻4 𝑂𝐻 𝑁𝐻4 𝑂𝐻 II. Salts of calcium are present in bones. They are Sodium potassium Potassium Sodium responsible for the strength of bones. These salts are tartarate Bitarate carbonate responsible for preventing heart attacks. Plaster of 𝐾𝑁𝑎𝐶4 𝐻4 𝑂6 𝐾𝐻𝐶4 𝐻4 𝑂6 𝑁𝑎2 𝐶𝑂3 Paris (CaSO4. ½ H2O) is used for broken limbs. Hydrochloride Ferric Hydroxide III. Potash alum is used to coagulate the blood coming Ferric chloride Acid 𝐻𝐶𝑙 𝐹𝑒(𝑂𝐻)3 out of a wound. It is also used for the purification of water. 22) Write the use of HCl IV. Salts of iodine are needed for the proper functioning I. For cleaning rust from the surface of metals. of thyroid glands. They are also used to set the II. For purification of Common salt (NaCl). treatment of goiter. III. To make aqua regia (3HCl + HNO3) used to dissolve noble metals such as gold. 17) What happened when IV. For making glucose from starch. i. Magnesium reacts with dilute HCl? V. For the proper digestion of food in our stomach. Magnesium forms its salt and release Hydrogen gas 23) Write the use of Nitric Acid HNO3 𝑀𝑔 + 𝐻𝐶𝑙 → 𝑀𝑔𝐶𝑙2 + 𝐻2 I. In the manufacture of fertilizers like ammonium ii. Sodium hydrogen carbonate reacts with dil. nitrate 𝑯𝟐 𝑺𝑶𝟒 II. For the manufacture of explosives Sodium salt and water and evolve carbon dioxide gas. III. In the manufacture of dyes, plastics and artificial silk. 2𝑁𝑎𝐻𝐶𝑂3 + 𝐻2 𝑆𝑂4 → 𝑁𝑎2 𝑆𝑂4 + 2𝐻2 𝑂 + 2𝐶𝑂2 IV. For etching designs on metals like copper brass and bronze. GOVT. ELEMENTARY SCHOOL CUSTOM ACADEMY WALTON CANTT LAHORE Page 10 of 20  GRADE 8 SCIENCE NOTES REVISED 2016 – 17 24) Write the use of Sulphuric acid 𝑯𝟐 𝑺𝑶𝟒 are neutral solutions. They have Ph = 7. PH = 7 is the Sulphuric acid 𝐻2 𝑆𝑂4 used in: midpoint of the scale. I. As a dehydrating agent Write the colours of some indicators in acidic and basic II. In the manufacture of fertilizers like ammonium solutions phosphate, calcium ammonium phosphate, calcium Original Colour in Colour in Indicator super phosphate etc. colour acid base III. In the manufacture of celluloid plastic, artificial silk, Litmus Violet Red Blue paints, drugs and detergents. IV. In petroleum refining, textile, paper and leather Phenolphthalein Colourless Colourless Pink industries. V. In lead storage batteries. Methyl orange Orange Red Yellow 25) Write the use of Acetic acid 𝑪𝑯𝟑 𝑪𝑶𝑶𝑯 Acetic acid used in: CHAPTER # 7 FORCE & PRESSURE I. In the preparation of pickles (ACHAAR) II. In the manufacture of synthetic fiber. 26) Write the use of Sodium Hydroxide 𝑵𝒂𝑶𝑯 1) Define Force (F) Sodium hydroxide used in: A quantity which moves or tends to move, stop or tend to I. Soap, textile and plastic industries. stop the motion of body is called force (F). II. Petroleum refining. 𝐹 = 𝑚 × 𝑎 𝑂𝑅 𝐹 = 𝑃 × 𝐴 III. Making rayon Force is measured in Newton (N) or Kgm/sec2. IV. In the manufacture of paper pulp and medicines. 2) Define Area 27) Write the use of calcium Hydroxide 𝑪𝒂(𝑶𝑯)𝟐 The space upon which force acts is called area. It is Calcium hydroxide used in: denoted by A. area is measured is m2 or cm2 I. In the manufacture of bleaching powder 3) Define Pressure II. As a dressing material for acid burns Force acting normally on unit area of a surface of an III. In making lime sulphur sprays to be used as fungicide object. Mathematically IV. As a water softener V. For neutralization acidity present in soil 𝐹𝑜𝑟𝑐𝑒 𝐹 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 = → 𝑃= 28) Write the use of ammonium Hydroxide 𝑵𝑯𝟒 𝑶𝑯 𝐴𝑟𝑒𝑎 𝐴 Pressure is measured in N/ m2 or in Pascal (Pa). Ammonium hydroxide used in: I. To remove grease from window panes 4) Define Hydraulics II. To remove ink spots from clothes The branch of science deals with the transmission of fluid III. As a regent in laboratory pressure through pipes as a source of mechanical force is IV. For the treatment of bee’s string called hydraulics. Such systems are often using to produce 29) What is PH Scale? large force with the help of small force. A scale used to measures the acidic or basic or alkaline 5) Define Pneumatics solution is known as PH scale. The branch of science deals with the study of applications 30) How we can measure PH of a solution? of pressurized gas to produce mechanical motion is called pneumatics. The PH can be measure with universal indicator or PH paper. A universal indicator paper has a mixture of several 6) State Pascal’s law dyes coated on it. It shows different colours for each PH Liquid filled in a closed containers fluid exerts equal values. pressure in all direction. This fact was first discovered by 31) Define indicator Pascal and called Pascal’s Law. A substance shows different colour in acidic and basic 7) What is an altimeter? Write its application solutions. e.g. phenolphthalein, methyl orange, litmus, An altimeter is an instrument used to measure turmeric, China rose and red cabbage. the altitude of an object above a fixed level. It is used in 32) What is Natural solution? I. Air crafts PH values range from 0 – 14. The solutions having equal II. Sky divers use wrist-mounted altimeter concentration of hydrogen ions (H+) and hydroxide (OH-) GOVT. ELEMENTARY SCHOOL CUSTOM ACADEMY WALTON CANTT LAHORE Page 11 of 20  GRADE 8 SCIENCE NOTES REVISED 2016 – 17 8) Differentiate between hydrostatic and atmospheric pressure Hydrostatic pressure Atmospheric pressure Greater the depth of the The earth is surrounded by water in the vessel, a cover of air called greater is the pressure atmosphere. The pressure of water. Such a liquid of atmosphere is called pressure that increases atmospheric pressure. 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑎𝑖𝑟 with depth is called 𝐴𝑡𝑜𝑠𝑚𝑝ℎ𝑒𝑟𝑖𝑐 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 = 𝐴𝑟𝑒𝑎 special fluid called brake oil. At one end of the pipe there hydrostatic pressure Pressure decreases with is a cylinder fitted with a small piston called master increasing altitude. cylinder. The small piston is connected with brake pedal. At the outer end of the pipe there is a second cylinder 9) Why supporting wall of a dam is built very broad at fitted with a large piston called slave cylinder. When small the bottom? piston is pushed into master cylinder by applying a small The supporting wall of a dam is built very broad at the force on brake pedal, the pressure thus produced is bottom because at bottom the water pressure is very transmitted without loss to the slave cylinder. The large large as compared to the surface of water. piston in the slave cylinder is pushed out with a large force. It pushes the brake pad out to make it rub against 10) Describe water pressure the moving wheel disc. It produces large frictional force The pressure exerted by water on the walls of the which stops the running wheel. container and bottom is called water pressure. Explanation: 12) Describe the use of Pneumatic system in daily life. I. Automatic tyres are inflated with compressed air. It is observed that speed of water coming out of tap on II. Spray guns use compressed air for spraying paints. ground floor is greater than the speed of water coming out of a tap on upper storey of our house. The speed of III. Compressed air is used in air powered tools like water depends upon the height of water. If water is on hammers and drills height then its speed is high and if water is at low height IV. It is also used in air brake system in heavy vehicles. then its speed is also low. 13) Describe Gas pressure in a container. 11) Application of Pascal’s Law- hydraulic system The molecules of a gas in container are in a continuous Jack System state of motion in all direction. There the molecule collides with each other and with the walls of the A small force F1 is applied on a small piston that produces container. These collisions exert force on the walls of pressure P on the oil. This Pressure P is transmitted container and thus produce pressure. through a pipe to a very large cylinder fitted with a piston. 14) What is aerosol? Since area of this piston is very huge. Hence a very large force is produced that is used to lift something very heavy “Sol” is a mixture of suspended solid or liquid particles in like a car. a gas or air. The product using “sol” systems are called aerosols. In figure valves V1 & V2 prevent the back flow of oil to the small cylinder so that heavy load remains rose up. When 15) Give six application of compressed air. I. Automobile tyres are inflated with compressed air for smooth running of vehicles. II. Spray guns use compressed air for spraying paint. III. Air powered motors use compressed air to work. IV. Pneumatics V. Brake systems VI. Most of dentistry tools use compressed air for their working. the oil stopper is opened, the oil in the large cylinder flows back to the oil tank and the load is brought down. REVIEWED BY: HAFIZ MUHAMMAD WAQAS SHARIF MPHIL PHYSICS Brake System SCIENCE TEACHER GOVT. ELEMENTARY SCHOOL It is a common example of a hydraulic system in a car. It CUSTOM ACADEMY WALTON CANTT LAHORE consists of a pipe and two cylinders. The pipe is filled with www.facebook.com/GESCAWL GOVT. ELEMENTARY SCHOOL CUSTOM ACADEMY WALTON CANTT LAHORE Page 12 of 20  GRADE 8 SCIENCE NOTES REVISED 2016 – 17 Length Measuring tape CHAPTER # 8 MEASUREMENT OF PHYSICAL QUANTITIES Volume Measuring cylinder Time Watch Atmospheric pressure barometer 1) Describe physical quantity and examples The quantities which can be measured are called physical Note: Solve all Numerical given at the end of chapter quantity. Examples: Time, Mass, Length, volume etc. 2) Define the term prefix. The words or letters added before SI units such as milli CHAPTER # 9 SOURCES AND EFFECTS (m), centi (c) & Kilo (K) are known as prefixes. OF HEAT ENERGY Prefixes are based on multiplying and dividing the units by power of 10. 3) What is meter rule 1) Write down the effects of heating and cooling on It is a one meter long graduated stick. It is used to solids measure the length of an object or distance between two Solid expand on heating and contract on cooling points. A meter rule is divided into 100 equal parts, each 2) Write down the effects of heating and cooling on part is equal to one centi meter. gases 4) Write a short note on Gas expand on heating and contract on cooling 3) Why is water not used instead of mercury in Measuring Flask thermometers? Flask is laboratory vessels (container). The flask is made of Because Mercury has high coefficient of expansion per plastic or glass. They are of different sizes and shapes. In unit rise in temperature school laboratory, 50ml, 100ml, 250ml, 500ml & 1000ml 4) Why one end of the iron girders is placed on rollers flask are used for making solutions. in construction of bridges? Measuring Pipette One end of iron girders is placed on the rollers along with Pipette is used to transfer a measured volume of liquid a gap at this end so that girder can move forward and from one container to another. They are of different sizes backward during expansion or contraction. and shapes. In laboratory 10ml to 25 ml pipette of glass or 5) Why gaps are left between two sections of a railway plastic are used. track? 5) What are SI units? Explain. The gaps allow the expansion and contraction of rails International system of units: in our daily life, we often during summer and winter season. need to measure various physical quantities with the help 6) Why do hot air balloons rise up? of some standard quantity. For example if we purchase Since hot gases rose up in air, so hot air in balloon causes sugar, we must come to know the quantity of sugar. Thus, it to rise up. there is a need of some standard quantity for measuring unknown quantity. This standard quantity is called unit. 7) Why do gases expand faster than liquids and solids? Because the particles of gases are widely disturbed i.e. Table of Units their particles are far apart from each other and they free Physical quantity Symbol Unit Symbol to move. Other 8) When a vessel containing a liquid is heated, the level Length l Metre m of liquid initially falls and then rises up. Why does it Mass m Kilogram Kg happen so? OR Time t Second s Describe the irregular expansion of liquid. Volume V Cubic meter m3 On heating the liquid water from 0 0C to 4 0C, it contracts so the level of liquid initially falls. But after 4 0C it expands 16) Write the names of measuring instruments which is so liquid rises up. used to measure the physical quantities. 9) What is thermal expansion? Explain it with the help Physical Quantity Measuring instrument of experiment. Temperature Thermometer The expansion of material objects on heating is called Mass Electrical balance thermal expansion. GOVT. ELEMENTARY SCHOOL CUSTOM ACADEMY WALTON CANTT LAHORE Page 13 of 20  GRADE 8 SCIENCE NOTES REVISED 2016 – 17 I. Take a metallic sphere which can pass easily through a move forward and backward during expansion and ring. contraction. II. Remove the sphere out of the ring. 16) Explain the expansion of liquids and with the help of III. Now heat the sphere and put it on the ring. an experiment. IV. It does not pass through the ring because of I. Take an empty flask and fit a cork into its mouth. Pass expansion due to heating. short limb of U-shape glass tube through it. V. On cooling the sphere, it attracts and passes through II. Clamp the flask in a stand. the ring again. III. Dip the long limb of U-shaped tube in the water. 10) What is Rivet and Riveting? IV. Note and mark at the level of water in glass tube and A rivet is a small, cylindrical and smooth shaft whose one then heat the flask. end is swollen (called Head) while the other end is flat. V. On heating, air in the flask expands and produces Hot rivets are used to join the metal plates. bubbles in the water. The process in which two metal plates are joined together VI. On cooling, air in the flask contracts, so suction is by means of rivets is called riveting. created which pulls the water in the glass tube up. 11) Demonstrate how a bimetallic strip works in a 17) Describe a simple experiment to study the thermal thermostat. expansion of Gases. In electric iron, when current passes through heating I. Take an empty flask and fit a cork into the mouth of element, it becomes hot. The connected bimetallic strip the flask. also heats up. On getting hot, it bends and is disconnected II. Limb of the U shaped glass tube through the cork. from heating element so, circuit breaks and switches off III. Clamp the flask in a stand as shown in fig. the electric iron. IV. Dip the long limb of U-shaped glass tube in the water. 12) Explain the peculiar (strange) behavior of water V. Note and mark a line at the level of water in the glass during contraction and expansion. tube. On heating the liquid water from 0 0C to 4 0C, it contracts VI. Now heat the flask. and its volume decreases while its density increases. On VII. Stop heating and let the system cool down to room cooling from 4 0C to 0 0C it expands, its volume increases temperature. and density decreases. VIII. Observe and note the level of water in the glass tube again. 13) What is thermometer? How it works? IX. The result is that the flask expands on heating and A thermometer is a device used to measure the produce bubbles in water. temperature. When some hot object touch the bulb of X. On cooling flask contracts and water level is pulled up the thermometer, the liquid inside the narrow tube in the glass tube. expands and rises up and we can measure the temperature by reading scale. 14) Explain the damages which are caused by expansion CHAPTER # 10 LENSES or contraction by giving two examples. I. In hot summer, the concrete used in roads expands. If no space is provided for its expansion, then road 1) Describe the paths of three rays which form image surface crack. after passing through a convex lens. II. Two sections of railway track are laid with gaps. If I. A ray parallel to principal axis after refraction from a there are no gaps, then they may be de-shaped due to convex lens passes through its principal focus (F). expansion in summer. 15) Describe the effects of expansion and contraction of solids. I. In hot summer, concrete in roads expands and road II. A ray incident on the convex lens after passing surface crack. through its principal focus (F) becomes parallel to II. Two sections of railway track are laid with gaps. If principal axis. there are no gaps, then they may be de-shaped due to expansion in summer. III. In bridges, one end of the iron girder resets on the rollers. A gap is also present at this end. So that it can GOVT. ELEMENTARY SCHOOL CUSTOM ACADEMY WALTON CANTT LAHORE Page 14 of 20  GRADE 8 SCIENCE NOTES REVISED 2016 – 17 III. A ray passing through the optical centre of the lens 7) Can an image be obtained on the screen by a goes straight without changing its direction. concave lens? Explain your answer briefly. The ray diagram of concave lens for different positions of the object show that rays diverge out and do not meet on the other side of the lens after I. refraction. Therefore real image is not formed, but virtual image is 2) Describe the paths of three rays which form image formed on extending the rays after passing through a concave lens. backward. I. A ray parallel to principal axis after refraction from a concave lens appears to come from principal focus (F). 8) How long our eye takes to acquire dark adoption at its maximum? When we suddenly move from bright light to dark area, the cone cells become de-activated but rod cell do not activated immediately so we can’t see things clearly. But after some time rod cells becomes active and we are able II. A ray pointing towards principal focus (F) becomes to see in the darkness parallel to principal axis. I. Cone Cell: It activate in bright light II. Rod Cell: It activate in dim light 9) Define short-sightedness and long-sightedness. In short-sightedness a person can see near objects clearly but distant object appear blurred. In long-sightedness a person can see distant objects III. A ray passing through the optical centre of the lens clearly but near object appear blurred. goes straight without changing its direction. 10) What is lens? Explain the difference between convex and concave lenses. Lens: A lens is a piece of glass or other transparent material like plastic whose one or both side is spherical. Types 3) Write the name of instrument in which convex lens There are two types of lenses. is used 1. Convex lens II. Camera 2. Concave lens III. Binoculars Convex lens IV. Magnifying glass Convex lens is thicker in the middle V. Contact Lens and thinner at the edges. 4) Define focal length. Concave lens The distance between the optical centre (O) and focus Concave lens is thinner in the middle and thicker at the point (F) of the lens is called focal length (f). Focal length edges. of a convex lens is taken as positive. 11) Define centre of curvature 5) How focal length is affected when the lens of eye The centre of the sphere of which a lens is a part is called becomes thicker? centre of curvature. It is denoted by “C”. In order to look something near to eye, ciliary muscles make the lens thicker and its focal length becomes shorter. So the image is formed on retina instead of point beyond it. 6) Upon what factor does the amount of light entering in a camera depend? The size of aperture. GOVT. ELEMENTARY SCHOOL CUSTOM ACADEMY WALTON CANTT LAHORE Page 15 of 20  GRADE 8 SCIENCE NOTES REVISED 2016 – 17 12) Define Optical centre 15) What is a real and virtual image? The centre of the lens is called optical centre. It is Real image denoted by “O” The image that can be obtained on the screen is called real image. Virtual image The image that cannot be obtained on the screen is called virtual image. 16) Why is real image not formed by concave lens? Explain your answer by ray diagram. In case of concave lens the ray diagram for different 13) Define principal axis and optical axis. positions of the object show that rays diverge out and do The line passing through the optical centre and centre of not meet on the other side of the lens after refraction. curvature of the faces of the lens is called principal axis or Therefore real image is not formed. Virtual image is optical axis. formed on extending the rays backward. The image is 14) Explain the ray diagram where the images would be always virtual erect and smaller in size. formed by convex lens for different distances of object. Also discuss the nature of images. I. When object is placed beyond 2F, then image is formed between F and 2F. The image is real, inverted and smaller in size. 17) Explain how eyes get used to darkness after sometime II. When object is placed at 2F, then image is formed at When we suddenly move from bright light to dark area, 2F. The image is real, inverted and equal in size. the cone cells become de-activated but rod cell do not activated immediately so we can’t see things clearly. But after some time rod cells becomes active and we are able to see in the darkness I. Cone Cell: It activate in bright light II. Rod Cell: It activate in dim light 18) Explain the defects in human eye. III. When object is placed between F and 2F, then image I. Short-sightedness (Myopia) is formed beyond 2F. The image is real, inverted and In short-sightedness a person can see near objects clearly larger in size. but distant object appear blurred. Reason When the eye lens becomes much thicker or eyeball becomes too long, the image of distant object is formed in front of the retina rather at retina. This defect is also called Myopia. Correction of the Defect IV. When object is at F then image is formed at infinity This defect is removed by using concave lens of suitable (∞) GOVT. ELEMENTARY SCHOOL CUSTOM ACADEMY WALTON CANTT LAHORE Page 16 of 20  GRADE 8 SCIENCE NOTES REVISED 2016 – 17 focal length (f). The concave lens diverges the light rays before they enter the eye. Hence the rays again meet at CHAPTER # 11 ELECTRICITY IN ACTION the retina. II. Long-sightedness (Hyperopia) 1) State the Principle of Power Generator In long-sightedness a person can see distant objects The basic principle is that the coils are kept stationary clearly but near object appear blurred. while magnet is turned inside the coil. The stationary coil Reason is called stator. The moving magnet is called rotor. When the eye lens becomes thin or eyeball becomes too 2) What are input devices? Give at least three short, the image of near object is formed beyond the examples. retina rather at retina. This defect is also called Any device that changes non electrical energy into Hyperopia. electrical energy in an electronic system is called input devices. Correction of the Defect Examples: Key board, mouse and microphone. 3) What are output devices? Give at least three examples. An output device converts electrical energy into other forms of energy Examples: Loud speaker, T.V screen, Monitor, Printer. 4) What is the difference between A.C and D.C? This defect is removed by using convex lens of suitable A.C (Alternating current) D.C (Direct current) focal length (f). The convex lens converge the light rays The current which The current which do not before they enter the eye. They are further bent by the changes its direction after changes its direction after eye lens to meet at the retina. an equal interval of time an equal interval of time 19) How do camera and human eye resemble with each is called Alternating is called Direct current other? What is the difference in their actions? current (A.C) (D.C) Examples Similarities Generators Cell, Batteries I. The retina of eye and film of camera serve the same purpose. 5) Name some basic components of electronics system II. Like camera, the eye lens forms a real and I. Resistors inverted image. II. Capacitors III. Pupil of eye is similar to the aperture of camera. III. Transistors Differences IV. Silicon chips In a camera lens can be moved back and forth the image V. Integrated circuits (IC) on film but eye lens cannot move. VI. Semiconductor diodes 20) Identify the properties of convex and concave lens 6) What is the function of solar panel? Properties Convex lens Concave lens 1. It converts solar energy into electrical energy. Positive focal length 2. Solar energy is used through solar panels. 3. During day light, electricity is directly used to run Negative focal length appliances and can also be stored in batteries for Thicker in the middle the use during night. Thinner in the middle Can form real image 7) Sketch an electrical generator and its important parts Diverging lens Always forms virtual image Converging lens GOVT. ELEMENTARY SCHOOL CUSTOM ACADEMY WALTON CANTT LAHORE Page 17 of 20  GRADE 8 SCIENCE NOTES REVISED 2016 – 17 8) Describe the working of power generator 13) What is wind energy? The basic principle is that the coils are kept stationary The energy produced by wind is called wind energy. The while magnet is turned inside the coil. The stationary coil kinetic energy (K.E) of wind in coastal areas is use to turn is called stator. The moving magnet is called rotor. huge blades mounted on high pole. This rotating blade The running water or fuels like, coal, oil or gas are used to runs the generators that produce electricity. run generators for producing electricity. 14) What is nuclear energy? In coal-fired electricity generation, the burning coal heats The energy produced by nucleus of an atom is called water in a boiler to produce steam. The steam pushes the nuclear energy. It is produced by nuclear fission. blades of a turbine fixed at the lower end of the rotor 15) What is nuclear fission? shaft. As the rotor spins inside the stator, electric power is Breaking a heavy nucleus into smaller atoms by fast generated. moving neutrons is called n