विज्ञान

Biology

Human Body

1. Human body is made up of very small blocks called cells. These contain a living substance called Protoplasm.

Systems of the Body

2. Skeletal system – The frame of the human body is made up of bones. It consists of 206 bones. It helps the body to stand, give shape to the body and also protects the inner organs like brain, heart etc. It also gives attachment to muscles. In the bone mellow RBCs are produced.

3. Muscular System – Comprises the flesh pieces under the skin. There are two types of muscles.

i. Voluntary muscles – which we can control.
ii. Involuntary muscles – which we cannot control. Eg. Cardiac muscles.

4. Digestive System – Comprises of 28 feet long tube. It helps in the digestion of food, produces blood and provides heat and energy to the body.

i. Mouth – Food is chewed in the mouth and here it mixes with saliva. Saliva is a fluid that comes to mouth from three pairs of salivary glands. It converts starch into sugar.

ii. Stomach – is a pouch made up of fine hair like projections. Here gastric glands coverts proteins into peptones.

iii. Small intestine – It is 22 feet long tube. Its secretion change starch into sugar and proteins into peptones. Thus a major part of the digestion process is completed in the small intestine.

iv. Large intestine – It segregates water from the food.

v. Liver – works as a store house for carbohydrates, minerals and vitamins. It helps to keep sugar level of the body constant.

5. Circulatory System – Digestive system helps in the formation of blood. Respiratory system purifies the blood while circulatory system circulates the blood to the different parts of the body. Impure blood from all parts of the body comes to heart which works like a pumping station. Heart pours the impure blood into lungs. Purified blood is again brought to heart to be distributed to all parts of the body. The vessels that take pure blood from heart are called Arteries and the vessels that take impure blood to the heart are called Veins.

6. Respiratory System – helps us to breath air in to lungs. Here oxygen combines with hemoglobin and is thus distributed to all the limbs.

7. Excretory System – Consists of lungs, skin and kidney. The lungs throw out waste matter of the body in the form of carbon dioxide. Kidneys are two been shaped organs on either side of the spinal cord. When blood flows through kidneys they strain out poisonous material which along with water is passed on to the urinary bladder. Skin throws out waste material in the form of sweat. Skin gives a sense of touch and protects inner organs and give shape and colour to the body.

8. Nervous system – Nervous system consists of brain and spinal chord. The brain controls the memory and other processes of the body.

9. Bladders – There are 2 bladders in the human body.

i. Gallbladder – Stores and produces Bile. Bile is a green coloured fluid. Bile is later poured into the small intestine and helps in removing poison from the blood.

ii. Urinary Bladder – collects waste material filtered out by kidneys and passes it down by two tubes called urethras.

10. Thyroid Gland is situated on the base of the neck. It controls the speed of the various body processes.

11. Pituitary Gland is situated near brain. It is also known as Master Gland. It controls other glands and determines the height of the individual.

12. Liver is the largest gland in the human body. It stores extra sugar in blood and releases sugar when it is required by the body. It manufactures urea and secretes bile.

13. Lungs – their main function is to purify blood with the help of inhaled oxygen.

14. Pancreas produces pancreatic juices and insulin which helps in burning carbohydrates. The deficiency of insulin causes diabetes.

15. Spleen – is the blush red organ situated left to the stomach. It is the birth place of WBCs and grave yard for RBCs. During fever and other infections spleen is enlarged and protects body by killing germs.
Blood

1. Blood is a red coloured fluid in the body which consists of RBCs, WBCs and Plasma.
2. Blood helps to maintain the temperature of the body. Removes waste material. Fight germs and carry hormones to the different organs.
3. Total volume of blood in a normal human being is about 5 ltrs. (60-80 ml per Kg)
4. RBCs are produced in Bone Marrow
5. Red compound in RBCs is Hemoglobin
6. Hemoglobin supply oxygen to the different parts of the body.
7. Dead RBCs are stored in spleen
8. Life cycle of RBCs is 120 days.
9. RBCs are also called Erythrocytes
10. Amount of Hemoglobin
11. Man – 14-15.6 g/100 cubic cms of blood
12. Woman 11-14 g/100 cubic cms of blood
13. Function of RBCs is to carry O2 to different limbs of the body
14. WBCs are formed in spleen.
15. Function of WBCs – defence mechanism of the body and protects body from invading bacterial.
16. Neutrophills – prevent attack of invading bacteria
17. Lymphocytes – produces antibodies
18. (Antibody is a substance produced in the blood in response to an Antigen or foreign body like bacteria, virus or toxic etc.
19. Besophils –secrete heparin (anticoagulant) which prevents blood clotting inside body.
20. Blood transfusion means administering blood of the same blood group to the blood stream of another person. Blood is divided into 4 groups ie., A, AB , B & O.
21. The blood in human body is oxygenated and purified in the lungs
22. Human blood was classified by – K. Landsteiner in 1900-02
23. Universal donor is – O
24. Universal acceptor is – AB
25. Rh factor was discovered by – K. Landseiner in 1940
26. Normal blood pressure – 120/80
27. Ratio of WBCs to RBCs in human body is 1 : 500.
28. Impure blood from all parts of the body enter Right auricle in heart.


Bones
1. Total no. of bones in human body – 206
2. Total no. of bones in babies is – 300
3. Largest bone is – Femur or thigh bone
4. Shortest bone is – stapes (in middle ear)
5. How many bones are there is skull – 28 bones
6. How many facial bones are there – 14 bones
7. Total number of muscles in human body – more than 400.

Human Eye

Eye works like a camera. Light waves reflected from the surface of the objects passes through the pupil of the eye and forms an image on the retina. This nervous impulse is sent by optic nerve to the brain. Thus the image is formed and understood.

Defects of Eye

1. Myopia or Short sightedness – In this case eye balls become more convex so the image formed is unable to reach the retina. Such a person cannot see distant objects. It can be corrected by using concave lenses.

2. Hyper metropia or Long sightedness – In this case eye balls become less convex thus the image is formed behind retina. Such a person cannot see near objects. It can be corrected by using convex lenses.

3. Astigmatism – In this case a person cannot see horizontal objects or vertical objects. It can be remedied by using cylindrical lenses.

4. Colour Blindness – When a person is unable to distinguish between colours especially red and green he is colour blind. Colour blindness is caused by the deficiency of Vitamin A. It is a hereditary disease.

5. Son of a colour blind person is likely to be colour blind because sexual inheritance finds easy way in case of males but not necessarily in case of females.

6. Nigh blindness is also hereditary and is caused by deficiency of vitamin A. Person suffering from night blindness cannot see objects clearly at night.



Human diet

1. Proteins – helps to build up tissues of the body and repair of worn out tissues. They are found in egg, meat, floor, rice, milk and more importantly in cheese, soya beans.

2. Fats – help in burning carbohydrates and work as reserve food found in butter, ghee and vegetable oil.

3. Carbohydrates – supply instant energy to the body. Found in potatoes, rice, wheat and sugar.

4. Mineral Salts – are slats of iron, calcium, and sodium. Salts of iron enrich the blood. Iron is found in green vegetables, apple and banyans.

5. Salts of calcium – help in the formation of bones and teeth. Calcium is found in eggs and milk.

6. The term vitamine was given by C. Funk – 1911.

7. Vitamin A – Retinol – is found in milk, butter, ghee, carrot, tomatoes, green vegetables, cord liver oil. Its deficiency causes anemia, night blindness, colour blindness and rickets.

8. Vitamin B – Seeds of roots, plants and yoke of egg. It helps in the growth, appetite and nervous system. Lack of it causes enlargement of liver and beri beri.

9. Vitamin B2 – Riboflavin – Milk, peas, beans, yeast, meat, egg and green vegetables.

10. Vitamin B5 – Niacin – Meat, fish, potato, whole grain, tomato, groundnut & green vegetables.

11. Vitamin B12 – meat, liver, milk.

12. Pholic Acid – Green Vegetables, sprouted pulses.

13. Vitamin C – Ascorbic Acid - Juicy fruits like oranges, lemon, tomato, cabbage, onions, amla and green vegetables. Lack of it causes defective bones, teeth and scurvy.

14. Vitamin D – Caleiferol - Found in milk, butter, cord liver oil and most importantly in sun rays. Lack of it causes Rickets.

15. Vitamin E – Tocopherol - Found in wheat, green vegetables, butter etc. lack of it causes Sterility.

16. Vitamin K – Synthesized by our body.

17. Water soluble vitamins are B-complex & vitamin C.

18. Fat soluble vitamins are vitamin A, D & K.

Human Diseases

Viral Disease
1. Viral – Rabies or hydrophobia is caused by rabies virus and its mode of transmission is bite of mad dog, monkey etc.

2. Small pox – is caused by Veriola Virus. Spreads by direct contact and also indirectly by injected articles.

3. Chickenpox – veressala virus. Spreads by direct contact and also indirectly by injected articles.

4. Dengu – Bite of Andes Mosquitoes.

5. Polio – Housefly and contaminated water.

6. AIDS – caused by HIV Virus. Caused by Blood transfusion, using infected needles, unsafe sex.

7. Hepatitis – Jaundice caused by Water.

Bacterial Disease - Diphtheria, phenomena, plague, TB
8. Malaria – caused by the bite of infected female anopheles mosquitoes.

Sl. No. Name of the Disease Effected part of the Body
1. Catarac Eyes
2. Dyptheria Throat
3. Jaundice Liver
4. Phenomia Lungs
5. TB Lungs, intestine
6. Tracuma Eyes
7. Diabeties Pancreas
8. Pyria Gums and Teeth
9. Manengitis Spinal cord and brian
10. Arthritis Joints and bones
11. Conjectivitis Eyes
12. AIDS Immunity system
13. Hippititus Liver
14. Aphasia Memory


1. Normal heart beat is 70 – 72/Min. in males 78-82/Min. in females
2. Largest gland in the human body is – Liver
3. Master gland is – Pituitary gland
4. Bile is stored in – Gall Bladder
5. Carbohydrates are stored in – Liver
6. What is the function of kidneys – to filter nitrogenous waste of the body from the blood and throw them out as urine.
7. Weight of the brain – 1.4 kg (male) 1.3 kg(female) – 3% of the body weight.
8. The largest part of the rain is – Cerebrum
9. Food is mainly digested in – small intestine
10. Gastric juices contain HCL (Hydrochloric acid) Acid.
11. Bile is stored in – Gall Bladder
12. Insulin is secreted by – Pancreas
13. Oestrogen is secreted by – Ovary
14. Testosterone is secreted by – testes
15. How many chromosomes are there – 46 (23 pairs)
16. Green colour of the leaves is due to the presence of chlorophyll.
17. Common cold is caused by – Rhinovirus.
18. What is the function of Kidney – Excretion of urine.
19. Hear burn refers to an uneasy sensation in stomach.
20. During day time plants absorb Co2
21. The genetic information is stored in – DNA
22. The main organ for digestion and absorption of food is – small intestine
23. Yellow fever is a viral disease transmitted by – Andes.
24. Proteins are mainly required for regeneration of cells
25. Strips on the back of animals are indicative of matching of skin colour with surroundings.
26. We feel drowsy after a heavy meal because brain receives less oxygen as blood rushes to supply oxygen and metrition to the contracting stomach and intestine
27. The hormone responsible for the secretion of milk in mothers is lactogenic hormone.
28. Which disease is known as ‘silent killer’ – Blood Pressure
29. Dialysis is used for a patent suffering form kidney trouble.
30. Elisa Test is done to detect the presence of HIV Virus.
31. Western Blot Testis the confirmation test of AIDS
32. Pulse reading is taken to find out heart beat
33. Typhoid is immunized by triple antigen.
34. Liver stores glucose as glycogen.
35. Test tube baby means fertilization of ovum takes place in the test tube and develops in uterus.
36. What is Leclamche Cell? – A modified form of simple voltaic cell, used zinc and carbon as electrodes, a saturated solution of ammonium chloride as electrolyte and manganese oxide as depolasiser.
37. Chromosomes not relating to sexual inheritance are called autozomes.
38. Heredity is controlled by jeans which is a segment of RNA and DNA
39. Egg laying mammal is - Spinster Ant Eater
40. Largest mammal is – Blue Whale
41. Ostomalisia is caused by deficiency of Vitamin D.
42. Types of Cells in Human body which form the function of transport of gasses is Erythrocytes.
43. Chemical name of Riboflavin – Vitamin B.
44. Latest development in Genetic Engineering is Gene Splicing.
45. Lymphocytes helps in formation of antibodies.
46. Ribosomes are related to protein synthesise.
47. Leukemia disease affects the blood cells in human body.
48. Iron is present in human body in the form of compound.
49. Gland which secretes hormones – Endocrine Gland.
50. Antibodies are administered to stimulate the production of antibodies.
51. Temperature regulatory function or thermostat in the human body is located in the Hypothalamus.
52. Plants that grow in saline soil is called Halophytes.
53. Tissue responsible for passage of water in plants in Xylem.
54. Histamine constricts or dilates the walls of blood vessels in the body.
55. Function of production of fibers and matrix in the body is performed by Fibroblasts.
56. Calcium and Phosphorus are essential for strong bones and teeth.
57. Test for testing Typhoid – Vidal test.
58. In our body tissues are bathed in Lymph.
59. Bacteriophage is a virus that attack bacteria.



Chemistry and Physics

1. The gas used in the artificial ripening of the fruits is – Acetylene.
2. Carburetor is used in an automobile to supply the mixture of petrol and air.
3. Gas responsible for Bhopal Gas Tragedy was Methyl Isocyanides.
4. The company responsible for Bhopal Gas Tragedy was Union Carbide Corporation of USA.
5. All acids contain the element Hydrogen
6. ‘IC’ chips for computers are made of Silicon.
7. ‘X’ rays are electromagnetic rays they are produced when electrons are stopped suddenly.
8. A vacuums tube that contains a filament, a grid and a plate is called a triode.
9. Picture tube of TVs etc. is cathode ray tube.
10. TV picture tube generally use electron guns of three primary colour red, blue and green.
11. Emission of electrons from a material by incident radiation is called photoelectric effect.
12. Coating of iron with zinc is called Galvanization.
13. The emission of an alpha-particle from a radioactive element decreases its mass no.
14. Radio carbon dating is a technique to estimate the age of fossils.
15. Beta rays are rays of high speed electrons.
16. Agents responsible for acid rain are so2 & No2.
17. The sensation of colour is due to wavelength of the light.
18. A blotting paper and a towel work by capillary action.
19. Soap is used in washing because it lowers the surface tension of liquids (Water).
20. Fastest growing tree is Eucalyptus.
21. Feeding of milk cattle with cotton seeds increase fat content temporarily
22. The two branches of a plant give two different fruits – tomatoes and brinjals by grafting one with the other.
23. Theory of Darwin – Survival of the fittest and struggle of existence.
24. Decomposition of organic material is due to Bacteria.
25. Beans helps in nitrogen fixation of the soil.
26. Cow which gives maximum milk yield – Jersey.
27. Plants manufacture carbohydrates (glucose or food) from CO2 and H2O in the presence of sunlight. In the process it liberates O2.
28. Hardest metal – Tungsten
29. LSD – is a narcotic drug viz. Lysergic Acid Diethylamide.

30. Why a beam of light passing through a prison produces a spectrum – Spectrum is formed on account to dispersion of light . The seven different colours viz. Violet, indigo, blue, green, yellow, orange and red have different angles of deviation.
31. What is hibernation – It is the winter sleep of frogs etc. In this dormant state they do not need much food.
32. The main harmful drug in tobacco is – Nicotine.
33. Ores of Bauxite is – Aluminum (Al2O3H2O2) Cryolite (Na3AlF6) Corndum (Al2O3)
34. How is milk pasteurized – By heating it to a temperature of 62oC (143oF) for half an hour. The treatment kill all bacteria which cause milk to go sour and all bacteria which are harmful eg. T.B.
35. Which mirror is used as torch light reflector – Concave.
36. The material used for blue coloured glass is added with cobalt oxide.
37. Liquid oxygen boils at –183o C.
38. Oxygen can be manufactured by evaporation of liquid air.
39. Ozone gas is more soluble in water than the oxygen
40. What is inertia – Everybody has a tendency to continue in its state of rest or of uniform motion. This inherent property of all matters is called inertia.
41. WLL – Wireless in Local Looping Technology.
42. Oil can be converted into fat by the process of hydrogenation.
43. Age of a tree is determined by counting the number of rings in its trunk.
44. Addition of Sodium Chloride to the food helps maintain the normal acid based balance of the body.
45. X-Rays are Electro magnetic radiations similar to light but of shorter wavelength.
46. Radio active isotope of hydrogen is called Deuterium.
47. Acids react with metals and hydrogen gas is released.
48. Electrons with (-) charge has – no mass
49. Protons with (+) charge has – 1 A.M.U. (Atomic Mass Unit)
50. Neutrons with (no charge) has – 1 A.M.U.
51. In Atom number of Protons = number of electrons.
52. Number of Protons is known as Atomic number.
53. Protons + Neutrons is known as Mass Number.
54. Beta Rays are high speed electrons.
55. Radio carbon dating technique is used to determine the age of fossils.
56. The emission of Beta particles increased the atomic no. by 1.
57. A very high frequency wave originating in the nucleolus of atom and traveling with the speed of light is the Gamma Rays.
58. Radio active sodium is used to detect leaks in water mains.
59. X-rays are produced when electrons are suddenly stopped.
60. Gingko and Cycas are examples of living fossils.
61. Chromosome number in a bacteria is 1.
62. Bacteria E coil is readily found in human intestine.
63. A bottle cork is chemically analyised found that it contain mainly carbohydrates.
64. Coriolis forces are produced by rotation of earth.
65. Potassium Permanganate is an oxidizing agent.
66. Hydroponics is the science of cultivating plants without soil.
67. A substance that changes into vapors without heating is called volatile.
68. Pearls are formed inside mollusks.
69. Temperature of air increases with height in Stratosphere.
70. Nitrogen is utilized by plants as nitrates.
71. Escape velocity is defined as the velocity with which a body has to be projected vertically upwards from the Earth’s surface so that it escapes and overcomes the earth’s gravitational field altogether.
72. Escape Velocity is 11.2 Km/Sec.
73. Kinetic energy of a moving body is defined as its ability to do work by virtue of its motion.
74. Potential energy – a body is said to have potential energy if by virtue of its position or state it is able to do work.
75. Speed of sound in air is 300 mts./Sec.
76. Speed of sound in water is 1400 mts./sec.
77. Speed of sound in solid is 5000 mts/sec.
78. Light waves are transverse waves whereas sound waves are longitudinal waves.
79. Feron oxide is coated on the tape of a tape recorder.
80. Communication satellites are placed in Ionosphere.
81. Horology is the science of measuring time and construction of time pieces.
82. Science of silk worm breeding is known as Sericulture.
83. D2O Deuterium (Heavy Water) is used as coolant in Nuclear Reactors.
84. Mercury and Bromine are two metals liquid at room temperature.
85. Fission – breaking up of a bigger nucleolus into smaller nuclei.
86. Fussion – combining of two smaller atoms to form a bigger nuclei.

Water
87. Pure waster is generally not found in nature. Rain water is the purest form of water. During its fall it dissolves carbon dioxide, sulphur dioxide, dust particles etc.
88. The expansion of water on freezing has various important consequences. The water that makes its way between cracks of rocks expands as freezing exerts great pressure on rocks leading to its pigmentation or denudation. In hill areas or sub-zero temperature water supply lines burst on account of freezing of water.
89. Since the ice that forms on a body of water like a river or pond is lighter than water that has not yet been frozen. It stays at the surface instead of sinking to the bottom. Thus the surface ice insulates the liquid water underneath it from the effects of freezing temperatures. In this way aquatic plants and animal life can survive in freezing temperature.
90. The specific heat of a substance is the hear required to raise the temperature of a gram of the substance by 10 C.
91. The specific heat of water is higher than that of other substances because a large amount of heat is required to break the hydrogen bond. Thus water can absorb a lot of heat with relatively little change in temperature i.e., why it is used in the cooling systems of vehicles.
92. Heavy Water or D2O is used as a coolant or a moderator in nuclear reactors. A certain amount of heat is required to change 1 grm of liquid into gas without average change in temperature. This is known as the latent heat or the heat of vaporization. Thus steam has more heat than water at the same temperature.
93. In case of water heat of vaporization is 539.6 calories per gram.
94. A sample of water containing soluble salts of calcium, magnesium and iron does not form leather with soap is called Hard water. Hardness of water is of 2 types.
95. Temporary Hardness – caused by the bicarbonates of magnesium and calcium. This type of hardness can be removed by boiling or by putting chemicals that is Clark’s Method.
96. Permanent Hardness of water is caused by the presence of sulphate chloride and nitrates of calcium and magnesium. It can be removed by adding chemicals like washing soda i.e., ion exchange method and by putting Zeolite.
97. Soaps are sodium salts of fatty acids.

98. Battery – is an electrical device that generates electrical current by converting chemical energy into electric energy. The essential components are positive and negative electrodes which should be of electrically conductive material, a separating medium and an electrolyte. There are 4 major types of batteries.
99. Primary batteries or Dry Cells – In this Zinc is the negative plate or alode and graphite acts as positive plate or anode with ammonium chloride as electrolyte. These are not reversible.
100. Secondary or storage batteries – In such batteries, lead sponge is the negative plate and lead oxide is the positive plate with sulfuric acid as electrolyte. These are reversible and can be recharged.
101. Fuel Cells – are super batteries in which solid electrolytes of lithium, titanium dioxide or titanium nitrates are used.
102. Solar batteries – Produce energy from the sun light.


General Science

103. Why does a ship rise as it enters the sea from a river – Sea water is denser than river water. Thus the upward thrust produced by the sea water on the ship is greater as compared to the river water.
104. How does a submarine float and sinks as desired – The submarine has a chamber in which water can be filled in or pumped out as required. That make it sink when water is filled in and to float water is pumped out.
105. Why the moisture gathers on outside of glass tumbler contain cold water – Because water vapors present in the air get cooled and appear as droplets of water on coming in contract with the cold surface of the glass tumbler.
106. Why does a thermometer kept in boiling water show no change of temp even when the water is continuously heated. – A liquid boils at a particular temp. and after that it will convert into vapors. Once the liquid starts boiling the thermometer reading remains constant because there is no further increase in temp.
107. In a vacuum flask, silvering reduces the loss of heat by radiation, vacuum reduces the loss of heat by conduction or convection
108. Which reading on both Centigrade and Fahrenheit thermometer is same - -40o C
109. Why does a body immunized in water weighs less – due to the upward thrust of water.
110. What keeps the glider up in the air – The upward thrust of air.
111. What controls the direction of the aircraft – tail unit of the craft.
112. Why motorists use convex mirror – its focal length is long so it gives a wider field of view. It gives virtual, erect and diminished image.
113. How is it that a needle sinks in water but a ship does not – ship displaces water which weighs more than its own weight (Archimedes principle)
114. Water preserved in a porous vessel is cooler, why – loss of heat i.e., latent heat of water in evaporation.
115. How does fish live in river where water is frozen – water has maximum density at 4oC and ice is formed at 0oC. The formation of ice starts at top while under the surface the temp. is 4oC. So fish can live.
116. Why do two eyes give better vision then one – It gives a three dimensional picture.
117. Why is the moon devoid of atmosphere – Moon’s thinness is 10-13 of the earth which causes low gravity. So gases emanating from the surface escape into inter planetary vacuum.
118. Why do clothes keep up warm during winter – Clothes prevent the heat of the body from escaping
119. In high mountain region bleeding through nose occurs because the pressure of blood in capillaries is higher than outsider pressure.
120. What is convection – It is the transfer of heat through a liquid or gas by the actual movement of atoms or molecules.
121. Why does ice float in water but sink in alcohol – Ice has less specific gravity than that of water but more than that of alcohol.
122. The burns produced by steam are deeper than those caused by boiling water as the same temp. why – Steam has more latent heat than what the water has a the same temp.
123. Why do we not feel the movement of the earth – because we are also moving at the same temp.
124. Why is mercury used in thermometers – It is a good conductor of heat and expands uniformally on heating.
125. Why is kerosene poured on stagnant water. – Kerosene being lighter than water, floats over the water and forms a film. It does not allow the air of the atmosphere to enter the water and help the mosquitoes to breed. (stops the supply of O2)
126. How is an electrical current carried from one place to another – It travels by flow of electrons through conductors.
127. A drop of water or mercury on a clean glass plate is circular in shape – why – surface tension in the case of a liquid drop is greater which makes its surface area minimum.(area of a spherical body is minimum.
128. Why does a train stops when chain is pulled – As soon as chain is pulled vacuum breaks and air rushes and brakes are applied.
129. Why does a red flower look red – It absorb all other colours of light except red colour.
130. Why is a compass used as an indicator of direction – The magnetic needle of a compass always lies in N-S direction under the influence of earth’s magnetic field..
131. Why does radio reaction improve after sunset – After sun set there are no ionizing radiations from the sun and so ionosphere which reflects radio wavers becomes more sable. This improves radio reception.
132. Why does the gun kick back when a bullet is fired - \to every action three is an equal and opposite reaction – Newton’s third law of motion.
133. Sun appears red during sunrise and sunset because light rays from the sun have to travel a longer distance since red colour has the longest wave length it is scattered in the atmosphere.
134. Why does a cyclist bend while taking a curved turn – He bends in order to make the centre of gravity remain within the base. This saves him form falling.
135. Why does a coin lying at a the bottom of a tall cylinder full of water seem to be raised. – Rays coming out from the coin bend outward due to refraction.
136. Why do diamonds shine at night – On account to high refractive index, the rays of light get totally internally reflected.
137. Why are we advised to empty our fountain pens before boarding a plane – Atmospheric pressure at higher altitudes is less than the pressure inside the pen so ink flows out due to lower pressure.
138. Why does a man lean forward while climbing a hill – A man leans forward so as to keep him in a stable equilibrium. Leaving increase the base of support so that the vertical line passing through the centre of gravity may fall with its base.
139. If we cross the atmospheric limits of the earth there is no atmosphere and scattering of light does not take place and sky appears black.
140. What is photosynthesis? - is a process in which plants prepare carbohydrates (their food). During day time in the presence of chlorophyll while consuming carbon dioxide and water. During this process they release oxygen. During night time since photosynthesis process stops and respiration continues plants liberate carbon dioxide. So it is not advisable to sleep under a tree at night.


Instruments

1. Instrument used to measure density of milk – Lactometer.
2. Blood Pressure is measured by – Sphygmomanometer.
3. Relative Humidity is measured by – Hygrometer.
4. An instrument used by the captain of a submarine or the commander of a tank to observe above and around them – Periscope.
5. Instrument used to check velocity of wind – Annometer.
6. Study of sound is called Acoustics.
7. Density of liquids – Hydrometer.
8. Sextant – used to measure angular distance between two objects


Units

1. Unit to measure pressure – Pascle.
2. Unit to measure Intensity of light – Gauss.
3. Unit of work is – Jules.
4. Unit for measuring Spectacle lenses is Diopter.
5. Unit of resistance is Ohm.
6. Unit of heat is Calorie.
7. Unit of capacitor is Faraday