Q. Give the name of a salt which is an essential constituent of our diet.
Ans. Common salt i.e., sodium chloride is an essential constituent of our diet.
Q. Why the glass bottle can be unscrewed easily on warming?
Ans. When we warm the neck of a bottle whose lid is screwed tightly, the lid expands to be unscrewed easily.
Q. Why are the stars visible only at night?
Ans. Stars are present both at day and night. But they are not visible in day because of the bright light of sun. So they are visible only at night.
Q. Why do clothes dry faster on hot day than on a cool day?
Ans. On a hot day temperature of the surroundings and the liquid is more than on a cool day. Hence the rate of evaporation is increased. So they dry faster.
Q. What is boiling point of a liquid?
Ans. Boiling point of a liquid is the temperature at which a liquid starts boiling and changes from liquids to gaseous state without undergoing any change in the temperature.
Q. What is the reason of a small gap between the rails on a railway track?
Ans. A small gap is provided between the rails on a railway track to allow for expansion of rails when the temperature rises during the summer.
Q. Why does one end of the bridge rest over the rollers?
Ans. One end of the bridge rests over rollers to allow the expansion of bridge when the temperature rises during the summer and due to the frictional force.
Q. Why does a glass tumbler sometimes crack when hot water is suddenly poured into it?
Ans. Glass is a bad conductor of heat. When hot water is poured suddenly into it, the inner layer of glass expands while outer layer does not expand. This difference in expansion causes the cracking.
Q. Why does a bicycle tube has more punctures in summer than in winter?
Ans. A bicycle tube has more punctures in summer than in winter because in summer air filled inside the tube expands due to high temperature.
Q. Why does sugar dissolve faster in hot milk than in cold milk?
Ans. In hot milk convectional currents are set up i.e., the hot milk being lighter rises up and is replaced by cold milk. Due to this, sugar dissolves faster in hot milk than in cold milk.
Q. Why does a spoon kept in hot tea become hot?
Ans. The spoon becomes hot because of the conduction of heat from hot tea to spoon.
Q. How does a thermos flask help to keep a warm liquid warm, and a cold liquid cold?
Ans. The construction of thermos flask is such that it avoids loss or gain of heat by conduction, convection as well as by radiation. As there is neither loss nor gain of heat it keeps a warm liquid warm and a cold liquid cold.
Q. Firemen wear helmets made of brass polished from outside. Why?
Ans. Brass polished helmets reflect most of the heat radiations and absorb very little while extinguishing fire.
Q. What are some important functions of water in the body?
Ans. (j) It acts as a medium of transport of various substances to the cells.
(ii) It excretes wastes outside the body and dilutes waste products and poisonous substances.
(iii) It helps in maintaining body temperature by sweating and evaporation.
(iv) It helps in the formation of urine and faeces.
(v) It helps to moisten the food and provides moist environment required by cells in the body.
Q- In what form L.P.G. present in cylinders?
Ans. In liquid form, when pressure is released, it evaporates and is obtained in gaseous form.
Q- Why we eat food? Act’ live. Energy is required to carry out the life – The food we eat gives us energy to do these activities, to grow, and replace the injured and damaged body cells.
Q. Why does ink leak out of a partially filled pen when taken a higher altitude?
Ans. The density as well as pressure of air goes on decreasing with altitude. When a partially filled pen is taken to a higher altitude, it le because the pressure of air acting on the ink inside the pen is greater than the pressure of air outside.
Q. Why do we feel weak and tired, when hungry?
Ans. When hungry we need energy as we have spent lot of energy ^ different activities. That’s why we feel weak and tired. After taking food we feel energetic refresh again because food gives us energy to work
Q. Why is light everywhere when the sun rises?
Ans. The light rays emitted by the sun come through the earth’s atmosphere and are scattered off in all the directions when they are reflected by the molecules of the air and dust particles. That is why we get light everywhere when the sun rises.
Q. Why does a man sitting under a fan feel cooler?
Ans. A man sitting under the fan feels cooler due to evaporation of sweat from his body. Fan circulates the air and increases the evaporation of sweat. Evaporation has cooling effect.
Q. Why do we hear more clearly in a curtained room than in a room without curtains?
Ans. Curtained rooms reduce the reflection of sound and audience hears only voice of the source and is not disturbed by reflections.
Q. What is heart beat? Does heart beat faster after exercise? Why?
Ans. The heart pumps out blood to arteries about 70 times per minute. This periodic contraction and expansion is called heart beat. The heart beat can be counted by counting the pulse.
The rate of heart beat increases after doing any sort of physical exercise. It is due to an increase in the requirement of energy. It increases the rate of oxygen flow in the blood.
Q. Name the two fluids which help in circulation in human body?
Ans. Blood and lymph. Blood flows in blood vessels and lymph in lymph vessels.
Q. What is the role of plants in controlling the air pollution?
Ans. Plants prepare their food in the presence of sunlight and water by absorbing carbon-dioxide from atmosphere. Greater the number oi plants, greater will be absorption of carbon-dioxide from atmosphere.
Q. Name the Oxygen-carrier present in blood?
Q. Would you call the smoking a cigarette as polluting the aft- Why? 1
Ans. Yes, cigarette smoking emits poisonous smoke which enters u‘ air. This smoke goes into the lungs of non-smokers and affects their health
q Sound travels in wood than in air.
Q If you want to hear a train approaching from far away, why • it more convenient to put the ears to the track?
Ans. The reason is that the track is made up of iron and the velocity f sound is very high in iron than in air.
Q. Venus is not a star. Even then it is called morning star. Why?
Ans. Venus is the brightest planet but sometimes it appears in the eastern sky just before the sun rise. So it is called Morning Star. Sometimes it appears in the western sky just after the sun set. Thus, it is also called Evening Star.
Q. What are heart beats?
Ans. As the heart pumps the blood into the arteries it contracts and then relaxes. This is called beating of heart. On an average the human heart beats 70 to 72 times per minute. It may beat 120 times or even more while doing hard work or exercise. Excitement or fear also increases the heart beat.
Q. Why are salts iodized? Why is goiter not seen people living on sea sides?
Ans. The salts are iodized to makeup the deficiency of iodine in the food. Iodine is an important component of hormone thyroxin, secreted by thyroid gland. The deficiency of thyroxin leads to various mental disorders and retarded growth. Thus, iodized salts are helpful in restoring the normalcy of thyroid gland and in turn, thyroxin.
The goiter is not observed in seacoast people, because they consume the sea food which contains high amount of iodine.
Q. Why is it more difficult to breathe on mountains than on plains?
Ans. With higher altitudes the pressure of air goes on decreasing. The oxygen content in the air is also reduced considerably. We experience difficulty in breathing on mountains because the pressure of air outside is less as compared to the pressure of air inside the lungs.
Q. A man is sitting in a moving bus. Is he in motion or not?
Ans. A person sitting in a bus is not changing its position in comparison to things inside die bus. So, according to the definition of motion, that man ls not moving. We know the bus is moving in comparison to trees and other buildings near the road. As that man is sitting in the moving bus, he is also moving.
Q. Name some common insect pests which damage the stored food grains.
Ans. Weevils, Grain borer, Red flour beetle, Almond moth, Saw- toothed beetle and grain moth.
Q- How do salt and sugar help in the preservation of fruits and Vegetables?
Ans. The spoilage in fruits and vegetables is caused by high moist content in them. The high concentration of salt and sugar removes the was from food materials through osmosis and thus prevents their spoilage h! Inhibiting bacterial growth. The micro-organisms already present in and vegetables die due to deficiency of water.
Q. Which type of engine is used in the automobiles such as car scooter, motorcycle, etc.? ‘
Ans. Internal combustion engine.
Q. Stray animals that you see on the roads or in the streets aro not called wild animals. Why?
Ans. The wild animals are those which cannot be domesticated or tamed. As the stray animals on the roads or in the streets can be easily tamed or domesticated they are not wild animals.
Q. Why bacteria and viruses are considered as “Immortal”?
Ans. Bacteria and viruses neither grow old nor die. Their growth remains continued for ever. They may survive a million year or even more if frozen or buried under salt. If they are buried in non-living environment they will stop growing but will not die. Whenever they get favorable living conditions, they will start growing again. Hence, they are considered as immortal.
Q. What is polluted air? Is tobacco smoke good for health?
Ans. Polluted air: The undesirable changes in the physical and chemical quality of the air which adversely alters the natural quality of the environment as well as affect badly on human health make the air polluted. The polluted air may contain C02, CO, S02, Pub, oxides of nitrogen and particulate matter including dust. These cause lungs infection, headache, eye and nasal irritation, coughing and chest pain, etc.
The tobacco smoke is not good for health because it contains nicotine and other gases which cause irritation to the lining of lungs and results in lung cancer, coughing and irritation in mouth, throat and nose.
Q. Why is the temperature range of clinical thermometer kept from 35°C to 42°C?
Alls. Clinical temperature is meant to measure temperature of the human body. The temperature of human body is 37 °C and temperature of human body does not vary beyond this temperature to large extent.
Q. Name the various types of thermometers.
Ans. There are many types of thermometers. For example:
1. Mercury Thermometer 2. Liquid Thermometer
3. Gas Thermometer
In mercury thermometer, the temperature is indicated by expansion of mercury. In liquid thermometers, alcohol is used as thermometric substance. In gas thermometers, gas like hydrogen is used as thermometric substance.
Q. How will you find out whether the water available in your locality
Ans. The water available in our locality may or may not be fit for
. kjne The water for drinking purpose should be pure and free from ‘ended impurities. Water may have suspended impurities rke clay, mud or silt. Suspended materials make the water turbid. These ‘pensions can be checked and removed by sedimentation or by adding alum and lime. Various bacteria are removed by Alteration through beds of sand, charcoal and gravel as in sewage plants.
The drinking water should be clean, colourless, odorless, transparent and free from bacteria. If water does not show above properties, it is not fit for drinking.
Q. How safe is it to drink water taken out through hand pump?
Ans. The water which is taken out from hand pump is safe for drinking provided that it should not be in the close vicinity of drained wastes. If the pump is situated at a place where wastes from farm animals and birds are drained, then the hand pump water will be polluted and will not be safe for drinking.
Q. How many planets are there in our solar system? Give the names of these planets in order of their distance from the sun.
Ans. There are nine planets in our solar system. The names of the planets in the order of increasing distances from the sun are given below:
1. Mercury, 2. Venus, 3. Earth, 4 Mars, 5. Jupiter, 6. Saturn, 7. Uranus, 8. Neptune, 9. Pluto.
Q. What is an alloy? Why are alloys made?
Ans. Alloy is a homogeneous mixture of metal with other metal or non- metal. Alloys are made so as to improve properties of metals. Alloys have properties different from constituent metals e.g., iron rusts but steel does not.
Q. What are thermoplastics? Give two examples of thermoplastics.
Ans. The plastics, which become soft on heating, are called ‘thermoplastics’. This property allows them to be set in a desired shape which is retained on cooling.
Examples of thermoplastics are polyvinyl chloride (PVC) and Polystyrene.
Q. Soap does not give lather with hard water, why?
Ans. Soaps react with calcium and magnesium ions present in hard water to form insoluble compound. That is why soaps do not give lather water hard water.
Q- What are the advantages when ethylene is mixed with wool to Prepare cloth?
Ans. When it is mixed with wool, ethylene is widely used for the Manufacture of suitings. It is commonly known as terewool. They have special properties which make them suitable for using in winter season
They are tough, strong, heat-resistant and do not catch fire so quickly reline clothes. They are dry-cleaned instead of washing with water. They are not so costly so woollen fibres. Pure woollen fibres are more suitable for hill stations.
Q. Why are cotton clothes being replaced by terylene clothes?
Ans. Cotton clothes are being replaced by terylene clothes because it is a strong thermoplastic and very resistant to action by chemical. It absorbs moisture to very less extent which makes terylene clothes dry out very quickly after washing. They are easier to wash.
Q. When someone opens a bottle of perfume, you can smell it from a distance. Why does it happen?
Ans. Molecules of gases are always in a state of random, ceaseless motion. When some one opens a bottle of perfume, you can smell it from a distance, because of the motion of perfume molecules.
Q. Why are white marks seen in our clothes during summer?
Ans. It is due to sweat containing mostly sodium chloride.
Q. How do vehicles cause pollution?
Ans. Vehicles such as cars, buses, trucks, scooters use petrol and diesel to move. Petrol and diesel produce smoke which consists of many gases such as oxides of carbon, nitrogen and sulphur. These gases of auto exhaust cause mainly air pollution.
Q. Can we boil water in fry pan made up of paper? If yes, why?
Ans. Yes, we can boil water in fry pan made up of paper because water will remain in contact with paper and does not allow it to attain its ignition temperature. Therefore, although paper is combustible but still it will not catch fire. Water will absorb heat from paper and start boiling.
Q. When you fry your food in oil, which vitamins are generally lost?
Ans. When we fry our food in oil, Vitamin C is generally lost because Vitamin C is destroyed by cooking.
Q. Why do fruits and vegetables get damaged more easily than food grains?
Ans. The fruits and vegetables get damaged more easily because their moisture content is more as compared to food grains. Secondly, they are also damaged due to faulty storage facility, improper handling and defective transportation facilities.
Q. What is a fuel? Give examples.
Ans. A material or substance, that burns to provide energy, is called a fuel, e.g., wood, coal, petrol, kerosene, diesel, liquefied petroleum gas (LPG). Solar energy, wind energy, and nuclear energy are new sources of energy.