2. (a) Why are water pipes apt to burst in cold weather?
(b) Which expand to the greatest extent when heated: solids, liquids or gases?
(c) In what units is quantity of heat measured?
Ans. (a) Water pipes burst in cold weather because water expands on freezing. (b) Gases, (c) Calorie B.Th.U. ‘
3. Why are leaves green?
Ans. Light consists of seven colours. A body looks red, blue or green, because it absorbs the rest of six colours and reflects only that particular colour to the eye. Green leaves look green as they reflect green colour, and absorb the rest six colours.
4. Why does radio reception improve after sunset?
Ans. Because there is less electrical disturbance in the atmosphere. The ionosphere which reflects radio waves becomes more stable in the absence of ionising radiation from the sun.
5. (a) Why does a straight stick look bent when partly immersed in water?
(b) Why does water boil at a lower temperature on the hills than on the plains?
Ans. (a) When the rays of light enter another medium, they change their course due to refraction, so the stick looks bent, when partly immersed in water.
(b) Because on hills the pressure is low, and lowers the pressure, the lower is the boiling point.”
6. Why does a cheap clock lose time in summer?
Ans. A cheap clock loses time in summer, because in summer its pendulum increases in length and the time for one oscillation increases, making the clock run slow.”
7. Why does a man fall forward when he jumps out of running train?
Ans. Man is in motion along with the train. As soon as he jumps out, his feet come to rest, while the body is still in motion due to inertia, so he falls forwards.
8. Why does water get cooled in earthen pitchers?
Ans. Pitchers have pores and water percolating through them evaporates. During evaporation heat is taken away from the water in the pitcher, and so it gets cooled.
9. An iron ball sinks, a ship does not. Why?
Ans. In case of iron ball, its weight is more than the weight of water it displaces. In the case of the ship, the space inside being vacant, the weight of the ship is less than the weight of water displaced. Thus whereas upward thrust is sufficient to balance the weight of the ship, it is inadequate to balance the weight of the ball.
10. What is the underlying principle in making of snow balls?
Ans. When the snow is pressed in the hands, its freezing point is lowered, a little of it melts and when the pressure is released, it brings the freezing point up to 0C° once more. The water which was formed, freezes again and binds the particles of snow together. The underlying process of melting under pressure and its re-freezing at the release of pressure is called relegation.
11. What causes the movement of glaciers?
Ans. It is due to the effect of pressure on melting point. (Freezing point decreases with increase of pressure). The bottom layer of ice tends to melt owing to the pressure of that above it. The resulting water flows out from under the glacier and when released from the pressure it freezes again ahead of the glacier.
12. Trace the course of petrol from the tank through the carburettor into the cylinder.
Ans. From the tank the petrol goes into the sediment catcher, where the sediment is removed. After this it passes through the fuel line, through the fuel pump and through a second fuel filter. Then it goes into the carburettor where it is mixed with the air and the air saturated with petrol vapours is sent to the cylinders.
13. What is the principle of the fluid fly wheel?
Ans. It consists of a metal fly-wheel with radial holes in which the fluid moves outwards on account of centrifugal force as it revolves. This gives greater inertia at higher speeds.
14. What is an electron, a neutron, a proton?
Ans. An electron is a negatively charged particle moving in orbits around the neutron of the atom. A neutron is an uncharged particle in the nucleus of every atom, except that of ordinary hydrogen. A proton is a positively charged particle in the nucleus, just about as heavy as the neutron, but carrying a positive charge.
15. What is radio-activity?
Ans. A few elements disintegrate themselves by radiating, and (alpha, beta and gamma) rays resulting in the formation of new elements; this process is known as radio-activity. Uranium, radium and thorium are the examples of radio-active elements.
16. What are the uses of radio-active isotopes?
Ans. Dozens of radio-active isotopes, made in atomic reactors, are used to detect where a substance goes and what it does in a living creature: they are also employed in medicine, metallurgy, industry and agriculture. They are mainly used as ‘Tracers’.
17. Helium is heavier than hydrogen; yet it is used in airships; Why?
Ans. Hydrogen is inflammable and hence dangerous, Helium is very much lighter than air, even though it is heavier than hydrogen. Hence it can be used in airships. It has the advantage of being not inflammable.
18. Why do we not see the stars in the day-light?
Ans. We do not see the stars during the day time because of the all around scattering of sunlight by the dust particles of the atomsphere, which makes the sky too bright for stars to be seen.
19. What is the difference between weather and climate?
Ans. Weather is the name given to the state of atmosphere day by day, and week by week, while climate is the usual kind of weather for a particular place, taken season by season.
20. What is the hurricane, a tornado, a cyclone?
Ans. Hurricane, a tornado and a cyclone are all similar kinds of storms, in which wind flows inwards spirally to the centre of low atmospheric pressure. A hurricane is a storm of wide extent that occurs in the West Indies region. A tornado is a more violent storm, its path of destruction is usually limited. Tornadoes are sometimes called cyclones. A storm like a hurricane that occurs in the region of the Indian Ocean is called a cyclone.
21. Why do stars twinkle?
Ans. The twinkling is caused by the differences in temperature of the air from point to point, and from moment to moment. These different parts of the air bend the star-light in different ways and at different angles. So they sometimes come through and sometimes not. Hence the twinkling.
22. What causes land and sea breezes?
Ans. The land has a lower specific heat than water, or in other words, it gets hot soon and also it loses heat quickly. During the day, the land has a higher temperature than the sea, so the breeze blows from the sea to the land; during the night the surface of the land is comparatively cooler, so the breeze travels from the land to the sea.
23. What is the difference between a comet and a meteor?
Ans. Meteors are small bits of mineral matter which weigh from a few ounces to even tons. We never see these meteors, unless they pass through the atmosphere and heat up to white heat on account of friction of the air.
A comet it looks like a star with a long tail moves in a long, oval orbit or path around the sun. The path of one well-known comet known as Halley’s Comet is so long that we may see it, once, only in seventy years. One of the latest comets is named after the Japanese astronomer Ikeya Saki, Kohoutek comet was discovered by a Czech born astronomer in 1973.
24. Why do we hear better on water than land?
Ans. Sound travels faster in water than air. Hence we hear better in water than on land.
25. What is 24-carat gold?
Ans. Pure gold is known in the jewellery trade as 24-carat gold. This is too soft a metal for ordinary wear, so a harder metal, generally copper, is alloyed with it. If the alloy has’ 18 parts of gold, 6 parts of another metal, it is 18-carat gold. If it has 14 parts of gold and 10 parts of another metal, we call it 14-carat gold and so on.
26. What is a graft?
Ans. Grafting is a method of propagating some kind of trees. A small stem is removed from the tree we wish to propagate, and this is tied to the young tree on which wc wish to graft. There is a tree in Arizona that bears lemons, grapes, limes and sixteen varieties of oranges.
27. Why does a bee hum?
Ans. The’ bee’s humming is caused by the rapid movements of its wings. To and fro vibration of the wings is extremely rapid, and this causes the sound that we hear.
The honey bee moves its wings back and forth 400.times a second. Their movements being extremely rapid, individual sound is not heard but instead we hear constant humming sound of the bees.”
28. How can bats fly in the dark?
Ans. When the bats are coming out of their cells, we do not hear any sound, though in fact they are usually making a series of sharp squeaks so high-pitched that the human ears cannot detect them. These high- pitched sounds are called ‘ultrasonics’ and have frequencies greater than 20 MHz
These sounds help the bats to avoid obstacles, because every solid thing reflects the echo, and the bats become conscious of the obstacle and the resulting possible danger. It is just like a radar.
29. How does a bat differ from a bird?
Ans. The wings of a bird, though formed by the forelimb, yet they consist of feathers, whereas in a bat, they consist of a membrane; moreover a bat is a mammal and is thus warm blooded.
30. Name three birds which cannot fly.
Ans. Kiwi, Emu and Ostrich.
31. What is protoplasm?
Ans. A jelly-like mixture of compounds of which the living matter is composed. It has not been possible to synthesise it so far. Julian Huxley has aptly described it as the physical basis of life.
32. What is chlorophyll?
Ans. It is a green pigment contained in the leaves of the plant. This green pigment enables the plant to absorb sunlight; and build up reserves of sugar; iron is a constituent of chlorophyll.
33. What is fossil?
Ans. These are remains of plants and animal life which become hardened like stone during the course of ages by the pressure of the upper layers. By examining them we learn about the plants and animals that lived on the earth in pre-historic periods. It also enables us to know the age of the earth.
34. Name three insects which are useful to mankind.
Ans. (i) Silk worm, (ii) Bee. (iii) Lacifer laeca, a small insect which produces lac.
35. What are fungi?
Ans. These are a class of organism resembling plants, which lack the green colouring matter, chlorophyll. ,Some of the plants belonging to this category are moulds, rusts, mildews, mushrooms..
36. Why is the path of water curved on coming out of a horizontal jet?
Ans. The gravitational pull attracts the water downwards, and the force of the jet pushes it forwards. The resultant of the two motions, one horizontal and the other vertical, provides it a curved or a parabolic path.
37. What happens to iron when it rusts?
Ans. It reacts with the oxygen of the air to form iron oxide which is the rust.
38. Why is mountain cooler than plains?
Ans. The mountain air is less dense, therefore, it absorbs much less heat from the rays of the sun. Hence the phenomenon.
39. What is the difference between ‘short wavelength’ and the ‘long wavelength’ in broadcasting?
Ans. Short waves are waves of high frequency, and are generally shorter than 50 metres in length. The long waves are those of lesser frequency, and are generally longer than 50 metres.
40. How would you distinguish between bleeding from an artery and bleeding from a vein?
Ans. Bleeding from an artery is characterised by red blood flowing out intermittently; whereas the veinous blood is purple, and its flow is continuous.
41. Certain parts of motor race courses are banked. Why is this done, and on which side of the driver is the highest point of the banking?
Ans. The race courses are banked to prevent skidding, when rounding corners. If the turn is to the left, the highest point of banking is to the right of the driver.”
42. What is the greatest practical height of a lift pump and why does it fall beyond that height?
Ans. Since the water in a lift pump is raised by the atmospheric pressure, the height of the lift pump would be slightly less than the height of the water barometer, i.e., about 34 ft. at sea level.
43. What is the function of the carburettor in a motor car?
Ans. Carburettor is the device where the fuel is metered; atomised into a fine spray; and mixed intimately with air before being sent to the cylinders. Only Petrol (i.e., Spark Ignition) Engines have caburettors.
44. What causes smoke to curl up in the air?
Ans. Hot gases rise, being lighter than air, and they follow a curved path owing to eddy currents being set up in the air. This curved path becomes visible when smoke is present in the gases.
45. How can a photograph be wirelesses?
Ans. The photograph is placed on a revolving drum and as this turns round, light is focussed upon it by lenses and a prism. The beam of light traces out a fine spiral on every point of the picture.
A perforated revolving disc, called the scanning disc, is intervened to interrupt the beam 1,300 times per second. This beam is thus broken up into dots of light reflected from the photo-electric cell.
The photo-electric cell, converts the light rays into electric impulses, which are amplified and transmitted on carrier current from a transmitting station. At the receiving station, the electric current is picked by an aerial. It is then amplified and passed on to an oscillograph mirror. Light from a lamp is directed upon this mirror and the light impulses are reflected through a slit.
The mirror is obscillated by the amplified aerial current and the rays received by it are reflected on a receiving drum, which has sensitised photographic paper round. Thus the photograph is reproduced at the receiving end.
46. Why must a parachute have a hole?
Ans. To avoid oscillation of the parachute while descending owing to the changing currents of wind, a hole in the centre of parachute is made, which allows the air to run out of the parachute regularly?
47. What is the use of a fly-wheel in an engine?
Ans. The momentum gained by the fly-wheel when spun by the pistons during the expansion stroke keeps the pistons moving during non-power strokes.
48. How is an aeroplane (heavier than air) able to fly in, the air?
Ans. It keeps itself in the air just as a kite does. The forces of an aeroplane in motion is: (i) weight, (ii) a forward pull due to the engine action, and (iii) the pressure of the air against the curved surface of its wings. When the engine starts and the propeller blades are rotated, the machine is pushed forward by the pressure of the air from behind, and as the plane pushes against the air; the air exerts a thrust depending upon the speed. If the upward component of thrust is greater than the weight the plane is lifted up.
49. What causes an eclipse of the moon?
Ans. When the earth comes between the moon and the sun, the rays of the sun are cut off and the shadow of the earth falls on the moon thus causing the lunar eclipse.
50. Why does not all the ink run out of a fountain pen when it is left with the nib downwards and the cover off?
Ans. The upward pressure of air stops the ink from flowing out.
51. Why are light and shade reversed in a photographic negative?
Ans. The photographic film is coated with silver salts. The brighter the light falls on it, the darker it becomes. The white parts emit more light than the dark ones and consequently affect the negative more, and thus making it darker.
52. What is artificial radio-activity?
Ans. When a light element is bombarded by alpha, beta or gamma particles or gamma rays nucleus may become unstable, which on settling down to a stable condition sends out radio-active rays. This phenomenon by which a stable element is rendered radio-active by artificial disintegration is called artificial radio-activity.
53. What is the object of transformer?
Ans. The object of the transformer is to transfer an alternating voltage from high to low and vice versa.
54. What is relay?
Ans. When the distance over which a message to be sent is very great, the current becomes too weak to work the sounder. It then becomes necessary to introduce an instrument which brings into use a local current at the receiving station. The instrument used for this purpose is called relay.
55. What is sound barrier, and explain why there is a bang?
Ans. Actually there is no such barrier. The term is a left-over from the days when it was feared that aircraft would not be able to fly faster than sound waves (around 1180 miles per hour) and that an aircraft trying to cross this limit of speed would come up against some mysterious obstacle.
The term is relevant today only in the sense that when an aircraft approaches the speed of sound and crosses it, there is heard what is called the ‘sonic bang’. This is the sudden release of piled up waves (or molecular disturbances); to understand the nature of which it is essential to know what sound itself is.
If sound may be defined a series of shock waves assailing the ear drum, and travelling at a measurable speed, it will be clear that an aircraft progressively speeding from 0 to 1200 km. p.h. will be piling upon its own wing-tips some of the shock waves which its own motion through the air has generated; that since the speed of sound is constant, the shock waves leaving the plane will be progressively reduced until a point is reached, when the speed of the plane will surpass the speed of the sound; then these accumulated shock-waves will be released at once, in mass hence the ‘bang’.
After the sonic ‘barrier’ has been passed, the aircraft will fly faster than sound when there are no disturbances to be piled up, nor will the sound waves of the approaching plane reach a listener earlier than the plane itself. Therefore, supersonic aircraft cannot be heard approaching.