1. How is sound produced ?
Ans: Sound is produced by a vibrating body e.g. when a tightly stretched bond is plucked, it vibrates and produced sound. When it stops vibrating , it does not produced any sound . 2. How is sound produced by humans? Ans: In humans, the sounds is produced by the voice box or the larynx. Put your fingers on the throat and find a hard bump that seem to move when you swallow. This part of the body is known as the voice box. This is at the upper end of the wind pipe. Two vocal cords are stretched across the voice box or larynx in such a way that it leaves a narrow slit between them for the passage of air. When the lungs force air through the suit the vocal cords vibrate, producing sound. 3. why the voices of men, women and children are different. Ans: The vocal cords in men are about 20 mm long. In women these are about 15 mm shorter. Children have very short vocal cords. This is the reason why the voices of men, women and children are different. 4. What is oscillatory motion Ans: The to and fro motion of an object is known as vibration. This motion is also called oscillatory motion. The number of oscillations per second is called the frequency. It is expressed in hertz. Its symbol is Hz. Amplitude and frequency are important properties of any sound. 5. On what factor loudness of sound deepens on? Ans: Loudness is property of sound that distinguish loud sound from bass . The loudness of sound depends on its amplitude. It is proportional to the square of the amplitude of the vibration producing the sound. When the amplitude of vibration is large, the sound produced is loud. When the amplitude is small the sound produced is feeble. The loudness is expressed in a unit called decibel(dB). Above 80 dB the noise becomes physically painful. 6. What is pitch? Ans: It is the characteristics of sound distinguish shrillness and pitch of the sound. When the frequency of the vibration is higher, then the sound has a higher pitch. When the frequency of vibration is lower, then the sound has a low pitch. The frequency of the voice of a child is higher than that of an adult. The voice of a woman has higher frequency and is shriller than that of a man. 7. What is range of the frequency of audible sound ? Ans: The sounds of the frequencies less than about 20 vibrations per second (20 Hz) are called inaudible sounds or infrasonic. Such sound can not be detected by the human ear. The sound of frequencies higher than about 20,000 vibrations per second (20 kHz) are called the ultrasonic sound. For human ear, the range of audible frequencies is roughly from 20 to 20,000 Hz 8. Why are sound waves called mechanical waves? Ans: Sound waves force the medium particles to vibrate. because of the interaction of the particles present in that medium 9. What is SONAR? Ans: SONAR stands for Sound Navigation and Ranging and it works on the principle of reflection of sound waves. The SONAR technique is used to determine the depth of the sea and to locate under water hills, valleys, submarines, icebergs sunken ships etc. 10. What is the intensity of sound? Ans: The amount of sound energy passing each second through unit area is called the intensity of sound. 11. Define : (i) Reverberation of sound. (ii)Echo (iii) Time period (iv)Wavelength. (v) wave velocity (vi) compression. (vi) rarefaction Ans: (1)The persistence of sound due to repeated reflection and its gradual fading away is called reverberation of sound. (2) Echo is a repetition of sound due to the reflection of original sound by a large and hard obstacle. (3) Frequency is defined as the number of oscillations per second. The time taken by the wave for one complete oscillation of the density or pressure of the medium is called the time period, T. (4) The distance between two consecutive compressions or two consecutive rarefactions is called the wavelength. (5)The distance traveled by a wave in one second is called wave velocity. It depends upon the nature of the medium through which it passes. (6) The part or region of a longitudinal wave in which the density of the particles of the medium is higher than the normal density is known as compression. (7) The part or region of a longitudinal wave in which the density of the particles of the medium is lesser than the normal density is called a rarefaction. 13. What through and crest. The point of maximum positive displacement on a transverse wave is known as crest. The point of maximum negative displacement on a transverse wave is known as through.
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Book resource: Science power Class 8th Check point [Formative Assessment] 1. Define Afforestation? Answer: The practice of planting more and more trees is called Afforestation. 2. What is desertification? What causes desertification? Answer: The phenomenon of converting fertile land into desert is called desertification. Deforestation causes desertification. 3. What is the effect of deforestation on rainfall and climate? Answer: Deforestation increases temperature and wind velocity that reduce rainfall. These changes led to climate change. 4. What is wild life? Answer: Wild life is an area where organism lives in their natural habitat like dense forest, jungle and water bodies. 5. Give one difference between endangered and vulnerable? Answer: Endangered are those animals that are not likely survive and will soon extinct where as Vulnerable are those animal which are likely to move in endangered category in future. 6. What is Red Data Book? Answer: Red Data Book is the source book which keeps a record of all the endangered animals and plants. 7. Name the first national park of India? When it was it established? Answer: A national park is protected land area that provide natural habitat to wild life. Jim Corbett National Park is the first national park of India established in 1936. 8. Name three different region of biosphere reserve? Answer: Core Zone, Buffer Zone, and Manipulation Zone. 9. Name the international body responsible for wild life conservation? Answer: World Conservation union 10. What is the objective of project tiger? Answer: To save tigers from unauthorized killing. 11. What are endemic species? Answer: Endemic species are those species of plants and animals which are found exclusively in a particular area and do not found anywhere else naturally. Related posts for 8th Conservation of Plants and Animals Conservation of Plants and Animals Download File Check point[Formative Assessment] Download File Science power [Solved Assessment] Download File C. Fill in the blanks:
1. Microorganisms may be unicellular or Multicellular. 2. Lactobacillus bacteria help to make curd from milk. 3. Disease causing microorganisms are called pathogen. 4. Ammonium salt in the soil is converted first into nitrites by -- Nitrifying ----- bacteria. 5. Casein coagulation takes place only when milk is hot . 6. Salting draws out water from food. 7. Nitrate in the soil are converted by ammonifying bacteria into nitrogen gas. 8. The process of preventing food spoilage by chemical or physical methods is called food preservation. D. Very Short Answer Questions: 1. Name any two antibiotics. Ans. Penicillins, streptomycin, tetracycline 2. Give the names of any two communicable diseases. Ans. Malaria , Typhoid 3. What are the two common food preservatives used at our homes: Ans.Salt,sugar,oil 4. Name two microbial diseases which spread through air, Ans. Common cold,flu,tuberculosis, influenza, small pox 5. Name any one unicellular algae. Ans. Cyanobacteria 6. Name any disease caused by virus in humans Ans. HIV E. Short Answer Type I Questions: 1. What is pasteurization? Ans. The process of heating milk at 70 degree for about 15 min and then cooling it for quickly is called pasteurization. This kill the most of the bacteria without affecting flavor. 2. How do leguminous plants increase the soil fertility: Ans. leguminous plants provide shelter to Rhizobium bacteria that help in converting atmospheric nitrogen present in soil into useable form that is taken by plants to make plant protein. 3. What is meant by nitrifying bacteria? Ans. Bacteria which help to convert ammonia present in soil into nitrates is called nitrifying bacteria. 4. How does female Anopheles mosquito spread malaria? Ans. Female Anopheles mosquito carries the malaria germ. When it bites a healthy person, he/she can get infected with malaria. 5. How do antibiotics work? Ans. Antibiotics kill or stop the growth of disease causing microbes F. Short Answer Type-II Questions: 1. (a) How do viruses differ from other microorganisms? (b) What is meant by fermentation? Ans. (a) A virus is a microorganism which exhibits characteristics of living as well as non-living things. (b) The conversion of sugar into alcohol in absence of oxygen using yeast is called Fermentation. 2. Explain the formation of curd from milk. Ans. Milk contains a sugar called lactose, when milk is heated to a temperature of 30-40 °C and a small amount of sour curd added to it, the lactobacillus starts to grow and convert the lactose into lactic acid and thus milk coverted into curd. 3. What is vaccine? How does it work? Ans. Vaccines are substance used to produce immunity to diseases in the living body. Vaccine consist of dead or weaken microbes .When these swallowed or injected into body of patient, the body produce antibodies to fight them. Antibodies remain in bodies and protect it from any future attack disease causing microorganism Value Corner 4. Microorganisms decompose dead organic waste of plants and animals and help in keeping the environment clean. (a) What would happen, if microorganisms do not perform this function? (b) Being a student, how can you contribute in keeping the environment clean! Give two ways. Ans.(a) air , water and soil get polluted if microorganisms do not decompose dead organic waste of plants and animals (b) (ii)Always follow 3R – Reduce ,reuse and recycle (b) Avoid wastage of natural resources and use them wisely and carefully. G. Long Answer Questions: 1. Explain two methods of food preservation. Also, discuss the advantages of food preservation. Ans. Food can be preserved in the following ways: (i) Heating: Heating food to a high temperature kills microorganism e.g water and milk. (ii) Salting: Salt prevents food spoilage by checking the growth of bacteria. Salt forces microorganisms to lose wafer by a process called osmosis. The advantages of food preservation are (i) Food last for longer period (ii) Food preservation prevents the food from being spoiled by the action of enzymes and microorganisms. (iii) It increases the availability of out of season foodstuffs. 2. Draw a neat diagram to show nitrogen cycle and explain the process of nitrification and denitrification. Ans. Nitrification is the process of conversion of ammonia into nitrates .It is carried out by nitrifying bacteria. Denitrification is the process of conversion of nitrates into free nitrogen gas. It is carried out by denitrifying bacteria. 3. Describe the principle on which the following methods of food preservation are based: (a) boiling (b) canning (c) freezing (d) dehydration Ans. (a) boiling: Heating to food at high temperature kill bacteria. (b) Canning: canning stop the supply of oxygen to bacteria and stop its growth. (c) freezing: it lower the temperature that reduce the growth of bacteria (d) Dehydration: it force bacteria to loose water by osmosis and stop growing further. H. HOTS (Higher Order Thinking skills) Questions: 1. Why do we say that if a person suffers from chickenpox once, he/she is not likely to be attacked by the same disease in future? Ans. when one suffers from chickenpox the body makes the antibodies that remain in body and prevent any future attack. 2. Why should we always wash our hands before handling food items? Ans: We should always wash our hands before eating to prevent the germs in our hands from entering the food so that we are prevented from getting diseases. Fore more book solution visit: 8th science Ch_02 Note: If you found any mistake Pls inform me at [email protected] for correction E. Short Answer Type-I Questions: 1. What is meant by agricultural implements? Ans: Agricultural implements are any kind of machinery or tools used on a farm to help with farming. The best-known example of this kind is the tractor. 2. How do legurninous plants help in maintaining the soil fertility? Ans: Rhizobium bacteria present in the root of legurninous plants convert the atmospheric nitrogen into ammonia into soil, which is used by plants. 3. What is pisciculture? Ans: Rearing of fish is called pisciculture. 4. Why is it important to sow seeds at a correct distance from each other? Ans: Seeds should be shown at a correct distance from each other so that seed get sufficient sunlight, nutrients and water from the soil. 5. Give two precautions that must be taken while sowing seeds. Ans: seeds should be shown with right spacing and at right depth 6. How does winnowing help in separation of grains from husk? Ans: When mixture of grain and chaff dropped on the ground from a height, The heavier seeds fall on the ground where as the lighter chaff gets blown away by the wind and fall at a distance. 7. Why is the spraying of pesticides harmful to us? Ans: The spraying of pesticides cause irritation to skin and respiratory problems. They get mixed with soil and water and absorbed by plants. These then enter our bodies through fruits and vegetables which we eat and cause us harm.. F. Short Answer Type-II Questions: 1. (a) Why is irrigation necessary? (b) Why is the drip system of irrigation a water- economical method? Ans: Rain varies and doesnot always supply the right amount of water at right time. Therefore it is important to supply water regularly to the crops. 2. Define fertilisers. Name any four fertilisers. Ans: Chemical substance that contain one or more nutrients essential for plants eg Urea., Calcium Nitrate, Ammonium Sulfate, Super Phosphate 3. The farmers of a village are celebrating the harvest festival of Baisakhi along with their families. They are dancing and singing traditional songs. (a) What is harvesting? Why do farmers celebrate Baisakhi? (b) What do we learn from celebrating festivals? Ans: (a) Cutting and gathering of mature crops is called harvesting. (b) Farmers celebrate Baisakhi to express gratitude to the Almighty for the bountiful harvest and pray for prosperity and good times in future G. Long Answer Questions: 1. (a) What are weedicides? (b) Name one weedicide. (c) What are the harmful effects of weeds in the crop field? Ans: Weedicides are chemicals that kill weeds (b) 2, 4-D and MCPA or Butachlor (c) Weeds compete with the crop for water mineral and sunlight and therefore reduce crop yield. 2.(a) Differentiate between manure and fertilizers. (b) What are the advantages of using manure? Ans: (a) Difference between manure and fertilizers. Fertiliser
Manure
(b) Organic manure is considered to be better than fertilisers. It is because of the following reasons to be (a) It enhances the water holding capacity of the soil. (b) It makes the soil porous, thus making the exchange of gases easy. (c) It also improves the texture of the soil. (d) It increases the number of friendly microbes. HOTs 1. Why do farmers level the field before sowing? Ans: For the uniform distribution of water and manure in a field, a farmer practices 2. During ploughing why is the land pressed lightly and not tightly? Ans: This is because loose soil allow root to breathe easily and allow root to penetrate deeper .Loose soil also help in the growth of earthworm and microbes that provide nutrients to soil.
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