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Ideal Answer How fish survives in cold countries

when the temperature falls below0oC?Water has the greatest density at4oC. In cold countries whentemperature falls and reaches 4oC,the surface water in ponds, lakes,and rivers goes down and settle atthe bottom. When the temperaturegoes down still further and reaches0oC a thick layer of surface waterturns into ice blanket. Theatmospheric temperature cannotpenetrate through thick ice blanketto lower the temperature at 4oC inthe bottom of the water body wherefish survives safely.

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Fill in the Blanks1. Heat engine converts heat in

to .........2. Diamond is an allotropic form

of .............3. ............. was the first space ship

to land on moon.4. The atmospheric pressure at

sea level is .............5. Indian Institute of

Astrophysics is in ––––6. Human eye contains .............

lens.7. ............. is employed as a

moderator in a nuclearreactor.

8. The hydrometer is aninstrument used to measure............. of liquids

9. The laws of electrolysis werepropounded by .............

10. ............. is used to measureangular distances betweentwo objects.

11. ............. is the apparatus formeasuring blood pressure.

12. ............. is used to measure thespeed of a moving vehicle.

13. ............. is used to determinethe concentration of saltsolutions by measuring theirdensities.

14. Sonometer is used to study thebehaviour of .............

15. ............. is used to calculate thecurvature of spherical objects.

16. ............. is used to see twodimensional pictures ashaving depth and solidity.

17. ............. is to hear and analysebeats of heart and lungs.

18. ............. is used to record smallintervals of time in thelaboratory, races etc.

19. ............. is used to convert aphotograph into a map.

20. ............. is an instrument usedto record speed of aeroplaneand motor boats.

21. Tangent galvanometer isused for measuring thestrength of .............

22. ............. is an instrument usedto measure the speed anddirection of motion of cloud.

23. By winding a watch, we store............. energy.

24. Beta rays are nothing butspeeding .............

25. The filament of an electricbulb is made of .............

26. The element mostabundantly found in theearth’s crust is .............

27. The element found on thesurface of the moon, which isalso described as ‘strategicmetal’ is .............

28. Thermocouple is used toconvert heat energy into............. energy.

29. .............. is an instrument tomeasure the pressure of gases.

30. The quantities that have onlymagnitude and not directionare called .............

31. Rate of change of velocity iscalled .............

32. The amount of water vapourin the air is termed as .............

33. The density of water ismaximum at ............. temper-ature.

34. Weight of a body at the centreof earth is .............

35. The escape velocity of earthis .............

36. The force of attractionbetween like molecules iscalled .............

37. The energy possessed by abody due to its position iscalled .............

38. Kinetic energy of a body is dueto its .............

39. ............. is the ability to dowork.

40. Fluids flow with zeroviscosity is called .............

41. ............. is used for measuringflow of liquids.

42. As temperature increasesviscosity of liquids .............

43. Surface tension decreaseswith ............. of temperature.

44. Liquid assumes sphericalshape due to .............

45. study of sound is known as.............

46. The speed greater than speedof sound is .............

47. ............. is used to reproducesound.

48. Rocket propulsion is based on.............

49. ............. is used to measureatomic distances. It is also theunit of wavelength of light.

50. . .. . . .. . . .. . . is the distancetravelled by light in one year.

51. Nautical mile is used innavigation. One nauticalmile is equal to ............. km.

52. One inch (in) is equal to............. cm.

53. One yard (yd) is equal to............. m.

54. One foot (ft) is equal to ............. m.55. One mile is equal to ............. km.56. ............. is the amount of heat

required to raise thetemperature of 1 gm of waterby 1o C.

57. One Acre (a) is equal to ............. m2

58. 1 Hectare (ha) is equal to............. acres.

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Answers to fill in the blanks1. Mechanical energy2. Carbon3. Lunic-II4. 1 bar5. Kodai Canal (Tamil Nadu)6. Convex lens7. Graphite8. Specific Gravity9. Faraday10. Sextant,11. Sphygmomanometer12. Speedometer13. Salinometer14. vibrating strings15. Spherometer16. Stereoscope17. Stethescope18. Stopwatch19. Stereoplotter20. Tachometer21. direct current22. Nephoscope23. Potential24. Electrons25. Tungsten26. Aluminium27. Titanium28. Electrical29. Manometer30. Scalar quantities31. Acceleration32. humidity33. 4o C34. zero35. 11.2 km/s or 7 miles/s36. cohesion37. potential energy38. motion39. energy40. Super fluids41. Venturimeter

42. decreases43. rise44. surface tension45. Acoustics46. supersonic47. phonogram48. Newton’s third law of motion.49. Angstrom50. Light year51. 1.82552. 2.5453. 0.91454. 0.304855. 1.60956. Calorie57. 10058. 2.471

Answer in a Word1. Name the instrument used to

measure the strength of anelectric current

2. Which metal is called themetal of future?

3. Which is the first nuclearresearch reactor of India?

4. Barometer was invented by -5. Intensity of an earthquake is

measured by-6. Raman effect is related with

the-7. The instrument which is

used to measure very hightemperatures -

8. The instrument which detectsthe presence of infrared raysis -

9. Name the quantity whichremains same before and afterthe immersion of two objectsof same weights.

10. Name the energy possessedby the water when it is colle-cted in the reservoir of a dam?

11. Which law states that stressby strain is a constant?

12. Echo and reverberation is dueto which phenomenon?

13. Sound travels fastest in whichmedium?

14. In a doctor’s stethescope, thesound is intensified becauseof which phenomenon?

15. Why does mercury is used asthe liquid in thermometers?

Michael FaradayMichael Faraday, FRS (September 22, 1791 –August 25, 1867) was an English chemist andphysicist (or natural philosopher, in theterminology of that time) who contributed tothe fields of electromagnetism andelectrochemistry.Faraday studied the magnetic field around aconductor carrying a DC electric current, andestablished the basis for the magnetic fieldconcept in physics. He discoveredelectromagnetic induction, diamagnetism and electrolysis. Heestablished that magnetism could affect rays of light and that therewas an underlying relationship between the two phenomena. Hisinventions of electromagnetic rotary devices formed the foundationof electric motor technology, and it was largely due to his effortsthat electricity became viable for use in technology.

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16. Adhesion is the force ofattraction between what typeof molecules?

17. Friction can be reduced bychanging over from whichfriction?

18. When a man circles round theearth in a spacecraft, whathappens to his mass andweight?

Answers to the answer in aword1. Ammeter2. Titanium3. Apsara4. Toricelli5. Richter scale6. Scattering of light7. Pyrometer8. Bolometer9. density10. potential energy11. Hooke’s law12. reflection of sound13. Steel14. reflection15. Because it does not wet the

glass, high density and hightermal expansivity.

16. Unlike molecules17. Sliding to rolling18. mass remains constant but

weight becomes zero

Explain the followingin a sentence or two1. light year2. Radiography3. Lactometer4. Seismograph5. Voltage6. Lightning conductor7. Rectifier8. Short circuit

Answers to thesententence or two1. Light year is a unit of distance

in astronomical calculations.It is the distance that lighttravels in one year at the speedof about 3 lakh km per second.

2. Radiography is the prod-uction of photographs of theinternal structure of bodiesopaque to visible light, by theradiation from X rays or bygamma rays from radio activesubstances

3. Lactometer is a scientificinstrument for testing thepurity of milk. It is based onthe principle of floatation.

4. Seismograph is an instrumentfor recording the intensityand origin of earthquakes.

5. Electric potential differencemeasured in volts is knownas voltage.

6. A conductor of electricityinstalled in a structure to saveit from lightning damage isknown as lightning condu-ctor. It neutralises the electriccharge of the clouds comingin its contact or carries it tothe earth.

7. Rectifier is a device forconverting an alternativecurrent into a direct one.

8. The direct flow of currentbetween two points ofdifferent potential is knownas short circuit.

Write Short Notes1. Laser2. EDUSAT Programme3. SRE4. CARTOSAT-25. Fibre Optics6. Direct to Home (DTH)7. Resonance8. Raman Effect9. Teleprinter10. Micro waves11. Cohesion12. Temperature scales13. Buoyancy14. Photo electric effect15. Fluorescence16. Super conductivity17. Super fluidity18. Piezoelectric effect19. Remote Control System20. Viscosity21. Phosphorescence22. Teflon23. Ultrasonics

TungstenTungsten also called wolfram is a chemical element that has thesymbol W (German: wolfram) and atomic number 74. A very hard,heavy, steel-gray to white transition metal, tungsten is found inseveral ores including wolframite and scheelite and is remarkablefor its robust physical properties, especially the fact that it has thehighest melting point of all the non-alloyed metals and the secondhighest of all the elements after carbon. The pure form is used mainlyin electrical applications but its many compounds and alloys arewidely used in many applications, most notably in light bulbfilaments, in X-ray tubes (as both the filament and target), and insuperalloys. Tungsten is the only metal from the third transitionseries that is known to occur in biomolecules.

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24. Black Box25. Escape Velocity26. Quautum TheoryAnswers to the short notes1. A Laser (Light Amplification

by Stimulated Emission ofRadiation) is an opticalsource that emits photons ina coherent beam. Laser lightis typically near-monochr-omatic, i.e. consisting of asingle wavelength, andemitted in a narrow beam.This is in contrast to commonlight sources, such as theincandescent light bulb,which emit incoherentphotons in almost alldirections, usually over awide spectrum of wave-lengths.In 1916, Albert Einstein laidthe foundation for theinvention of the laser, whilethe first working laser wasmade by Theodore H.Maiman in 1960.

2. EDUSAT programme isaimed to provide distanceeducation service usingadvanced space technologyand ground technology ofconvergence.

3. Space-capsule RecoveryExperiment (SRE) is intendedfor demonstrating thecapability to recover anorbiting space capsule.SRE will be launched as a co-passenger of CARTO-SAT-2on board PSLV during thesecond half of 2006-2007.

4. Cartosat-2, the twelfth in theIndian Remote Sensing (IRS)satellite series, is anadvanced remote sensingsatellite capable of providingscene-specific spot imagery.

5. Fibre optics, also spelled FiberOptics, is the science of

transmitting data, voice, andimages by the passage of lightthrough thin, transparentfibres or some othertransparent material of highrefractive index.In telecommunications, fibreoptic technology has virtuallyreplaced copper wire in long-distance telephone lines, andit is used to link computerswithin local area networks.Fibre optics is also the basisof the fibrescopes used inexamining internal parts ofthe body (endoscopy) orinspecting the interiors ofmanufactured structuralproducts.The principle on which thistransmission of light dependsis that of total internalreflection.

6. It is a system of TV broad-casting where TV signals aretransmitted directly toviewers, side stepping thecable operators. The viewerneeds decoder to synchronize

the signals with TV sets. TheDTH system has highestquality visual and audiosignals. The system makesuse of advanced digitalcommunication and videocompression technique. Itfunctions on the basis of KU-band transponders. Thisimplies that DTH providerswould be in the position tooffer value added service likeinteractive media, tele-shopping, etc.

7. Resonance is a phenomenonof forced vibrations due towhich sound waves can beproduced with a largeamplitude or intensity. Allbodies have their naturalfrequency of vibration. Whenwe apply a small signal of thesame frequency to the body,the signal is greatly amplifiedand this is called reonance.

8. When monochromatic light ispassed through a transparentmedium, it is scattered. Thescattered light containsoriginal wavelength as wellas lines of larger and shorterwavelengths than theoriginal line, such wavelengths are called Ramanlines and the effect is calledRaman Effect.

9. Teleprinter is a telegraphtransmitter with the help ofwhich we can send more than50 words per minute toseveral stations simultane-ously without any strain to theoperator and none whatso-ever to the receiver. Theperson at the sending stationpressesr the key on the keyboard which is just like thatof a typewriter, correspon-ding to a particular letter. Atthe receiving station the letteris recorded automatically.

Light-yearA light-year or lightyear is aunit of measurement of length,specifically the distance thatlight travels in a vacuum in oneyear. While there is noauthoritative decision on whichyear is used, the InternationalAstronomical Union (IAU)recommends the Julian year.Numerical valueA light-year is equal to:9,460,730,472,580.8 km

(about 9.461 Pm)5,878,625,373,183.61

statute milesabout 63,240 astronomical unitsabout 0.3066 parsecs

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10. High frequency radio waveswhose wavelength is less thanabout one metre are usuallydesignated as microwaves.These are electromagneticwaves travelling with thespeed of light, i.e., 3 × 108 m/s.

11. The force of attractionbetween the molecules of thesame substance is calledcohesive force and thisproperty is called cohesion.Due to this property themolecules of the substanceare held together. Cohesiveforce is maximum in the caseof solids, less in liquids andminimum in the case of gases.The definite shape of a solidbody is due to cohession.

12. Three systems of temperaturemeasurement are now in use-the Celsius scale, theFahrenheit scale and the KelvinScale. The Celsius scale wasworked out by the SwedishPhysicist, Anders Celsius in1742. The Fahrenheit scale wasdevised by the German bornPhysicist, Gabriel DanielFahreinheit around 1715. TheKelvin scale was devised by theBritish Physicist, WilliamThompson Kelvin.Conversion FormulaCelsius to KelvinK = C + 273.16

Fahrenheit to CelsiusC = (F-32) x 5/9Celsius to FahrenheitF = C x 9/5 + 32

13. A body seems to weigh lesswhen immersed in a liquid,but the moment it comes outof water, the same bodyseems too heavy to be easilylifted. We conclude that aliquid exerts an upthrust ona body immersed in it. Thetendency of a liquid to exertan upthrust on a bodyimmersed in it is calledbuoyancy and the upthrust iscalled buoyant force.

14. When visible light, ultra violetrays, X-rays etc., fall uponcertain metals (caesium,rubidium, pottassium) elect-rons are liberated from them.This phenomenon is knownas photo electric effect.

15. The luminescence obtainedwhen certain substanceabsorb radiation of one wavelength and emit light ofanother wavelength is knownas fluorescence.

16. Super conductivity is aphenomenon of completedisappearance of electricalresistance and appearance ofdiamagnetism in certainsolids when they are cooled

to near absolute zero or verylow temperature.

17. All liquids have viscosity atroom temperatures. However,as the temperature goesdown, helium, which isavailable in gas form, getstransformed into liquid formand its viscosity becomeszero. This means no apertureis too narrow for it to flowthrough. This property iscalled super fluidity.

18. The production of currentwhen mechanical pressure isapplied on certain dielectric(electrically non-conducting)crystals such as quartz andRochelle salt. The applicationof stress distorts thearrangement of ions in thesecrystals and an electric fieldis built up. This effect isknown as direct piezoelectriceffect and is used in deviceslike electronic gas lighters,microphones, phonographpick-up needles, etc.Conversely, application of anelectric field across certainfaces on the crystal results inmechanical distortion of thecrystal. This effect is knownas reverse piezoelectric effectand is used in devices whichconvert electric signals intomechanical vibrations.

19. A system in which theoperations of a unit arecontrolled from a distance, inother words, there is a substa-ntial distance separating theoperating unit and thecontrolling unit. The operatingunit may range from atelevision set to guided missileand the distance may varyfrom a few meters to a fewhundred kilometres. There arethree essential components ina remote control system - acontrolling quantity, atransmission medium and a

Anders CelsiusAnders Celsius (November 27, 1701 – April 25,1744) was a Swedish astronomer. Celsius wasborn in Uppsala in Sweden. He was professorof astronomy at Uppsala University from 1730to 1744, but traveled from 1732 to 1735 visitingnotable observatories in Germany, Italy andFrance. Celsius founded the UppsalaAstronomical Observatory in 1741, and in 1742he proposed the Celsius temperature scale in a

paper to the Royal Swedish Academy of Sciences. His thermometerhad 100 for the freezing point of water and 0 for the boiling point. Thescale was reversed by Carolus Linnaeus in 1745, to how it is today.

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controlled quantity. Mostcontrolling quantities sendsignals to the controlledquantity through infrared raysor radio waves or lasers or ultrasonic waves. The commonTV/VCR remote controlsystems use infrared pulses.

20. The property of a liquid by virtueof which it offers a resistance tothe flow is called viscosity.Viscosity is internal friction ofa fluid. Viscosity is due to thecohesive forces between themolecules of the liquid. Greaterthe cohesion or cohesive forcesbetween the molecules of aliquid, larger is the oppositionof the liquid. Thus honey whichhas more cohesive forces thanwater displays greater viscositythan water

21. It is the form of luminescencein which a substance emitslight of higher wavelengthafter absorbing an electrom-agnetic radiation. Phosphore-scence may continue evenafter the source of light is cutoff.

22. An organic substance madeby the polymerisation oftetrafluoroethane, CF2

= CF2.The chemical name of teflonis polytetra fluoroethane.Because of its properties highresistance to heat, chemicaletc. It is used to coat non-stickcooking materials, electricalinsulation etc.

23. The Science of sound wavesof frequency greater than theaudible range, i.e., greaterthan 20,000 Hz (20 KHz). Thevibrations of certain crystals(quartz, zinc oxide, bariumlitanate etc) under theinfluence of an appliedalternating voltage producesultrasound or ultrasonicwaves up to well above 20KHz. In the medical field,

ultrasound is used to detectand diagnose tumours,gallstones, heart diseases,distinguish between diseasedand healthy tissues, monitorthe development of the foetus,destroy diseased tissue etc. Inindustry, ultrasound is usedto measure the thickness ofpipes,detect cracks or leakea-ges in pipes, flaws in metalcastings and in sonar devices.

24. The black box is a term usedfor a self contained unit ofelectronic circuit which isorange in colour. Inaeronautics, this device isknown as flight recorder. Itrecords data on thefunctioning of an aircraft andits systems on a tape. Therecorder is contained in acrash - proof, floatable boxwhich is ejected in case of anaccident and is usually fittedwith a homing radio beaconand flashlight to reveal itspresence. In routine flights ofairliners it traces faults formaintenance control. Byanalysing the data stored inthe black box the cause of thefailure of the aircraft can beknown.

25. It is the velocity that aprojectile, space probe etc.,must have in order to escapethe gravitational field of aplanet or the moon. It dependson the mass and diameter ofthe planet. The escapevelocity is about 11.2 km/s forthe earth and escape velocityof moon is 2.37 km/s

26. According to this theory,changes of energy in atomsand molecules occur only indiscrete packets, each anintegral multiple of afundamental quantity (h)generally referred to asquantum. Light packet

having energy h is calledphoton.

Scientific Reasons Blotting paper absorbs ink.

Why ?The blotting paper is porousand has a number ofcapillaries of very fine pores.When a portion of the blottingpaper is brought in contactwith the ink, it enters thecapillaries due to the surfacetension.

. Why does carbon dioxide isused in extinguishing fire?Carbon dioxide being heavierthan oxygen acts as fireextinguisher by cutting off itsoxygen supply to a burningobject.

Why do the stars twinkle ?Stars appear to twinklebecause its light travelsthrough different layers ofspace of varying densities. Asa result the light from the starsbends and makes themappear to blink on and off.

Why is it not possible to seethe stars in the day light ?The blazing light of the sunduring daytime prevents theless intense light of the starsfrom being seen distinctly.

Why does the ice float onwater while it sinks inalcohol?The specific gravity of ice isless than that of water but thesame is more than that ofalcohol, hence ice floats onwater but sinks in alcohol.

Why is mercury used inthermometer ?Mercury is the only metalwhich is in liquid state evenat the ordinary room tempe-

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rature. Also, it uniformlyexpands when heated anddoes not stick to the walls ofthermometer. Its high boilingpoint and low freezing pointis the main reason for using itin ordinary thermometers.

How can bats fly in the darkavoiding obstacles?The ultrasonic waves produ-ced by bats during flying arereflected back when they hitthe obstacles. Hence, bats canfind their path without anydifficulty.

Why does water pipe oftenburst in cold countries?In winter, the water in thepipes freezes. On freezing intoice the water increases involume, which results inbursting of water pipes.

Why is cooking quicker inpressure cooker ?In a pressure cooker, boilingpoint of water is raised byincreasing pressure withsteam. Food gets hightemperature and so cookingbecomes quicker.

We bring our hands close tomouth while shouting tosomebody at a distance.Why?By bringing the hands closeto our mouth, the soundenergy is not allowed tospread in all directions,rather being made unidirec-tional (i.e. directed in aparticular direction). Hencethe sound produced becomeslouder.

Why do we lean forwardwhile climbing a hill ?Leaning forward enables usto keep the line passingthrough the centre of gravityvertically downward, within

our feet, and thus theequilibrium is kept stable.

Why are lightning conduc-tors fixed at the top of highbuildings ?When an electric dischargetakes place from the cloud, thelightning conductor providesit an easy conducting path tothe earth without damagingthe building.

Why does a parachute musthave a hole ?A hole in the centre ofparachute is made to avoidoscillation of the parachutewhile descending owing tothe changing currents ofwind. The hole allows the airto run out of the parachuteregularly.

How does a flute producedifferent sound notes?A flute produces differentsound notes because airparticles passing through itare vibrated with differentfrequencies with the closingand opening of the holes.

Why do we use a fuse in anelectric circuit?A fuse is used in an electriccircuit because when excesscurrent flows through thecircuit the fuse melts andbreaks the circuit andprevents the damage to anyof the electrical goods used.

What causes wind ?Winds are caused by theunequal heating of the earth’ssurface and rotation of earth.

Why does a drop of liquidassume a spherical shape ?A drop of liquid assumes aspherical shape due tosurface tension. A sphere hasthe least surface area for agiven volume.

What is a breeder reactor ?A breeder reactor is such areactor which produces morefissionable material than itburns.

What does a moderator do ina nuclear reactor?The number of nuclei split bythe impact of neutrons isregulated by a moderator in anuclear reactor.

Why is a small space left at thejoint between the two rails?To permit the expansion ofrails due to heat generated byfriction of the moving train insummer.

A glass tumbler is filled to thebrim with water and a pieceof ice is floating on it. As theice melts, will the wateroverflow or not? Give reasonfor your answer.Level of water remainsunchanged because thevolume of water produced bythe melting of ice is exactlythe same as that of the pieceof ice. On melting, the waterwill be equal to the volume ofwater displaced by the ice.

When a moving train slowsdown quickly, will a passen-ger tend to fall backward orforward? Explain why?The passenger will tend to fallforward because the lowerportion of his body which isin contact with the seat willcome to rest quickly whereasthe upper portion of the bodycontinues to be in a state ofmotion. Hence, the person isthrown forward, due to inertia.

Explain why it takes moretime to cook meat andvegetables at hill stations?At higher altitudes, theatmospheric pressure is low

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as compared to that in theplains and, therefore waterboils below 1000C. Hencesufficient heat is not suppliedfor cooking the meat andvegetables at hill stations.

When we drink soft drinksthrough a straw, why doesthe liquid go up into ourmouth?When a person sucks air fromthe straw, the pressure of theair inside the straw is reducedas compared to the atmosp-heric pressure acting on thesurface of the liquid. Therefore,the soft drink rushes up intothe straw and to the mouth.

Explain why the moisture(water droplets) gathers onthe outer side of a glasstumbler containing ice-coldwater?The water vapour present inair gets cooled and appear asdroplets of water on comingin contact with the coldsurface of the glass tumbler.

Why does a metal seen colderin winter and hotter insummer compared with apiece of wood?Metals absorb and transmitheat more rapidly than wood.

A thick glass tumbler oftencracks when a very hot liquidis poured in it. Why?The inner surface of the thickglass tumbler coming incontact with the hot liquidexpands more in comparisonto the outer surface which isrelatively at a lowertemperature. The unevenexpansion of inner and outersurface may produce cracks.

How does a rainbow form?Explain the phenomenon.After rain, some cloudscontinue to linger in the sky

and they contain waterdroplets. Water droplets actlike prisms. Sun’s rays fallingon water droplets sufferdispersion and produce aspectrum. The differentcolours are viewed in the formof a rainbow.

What causes the rumblingsound of thunder?Air is heated instantly whenan electrical charge oflightning passes through it.The heat causes themolecules of air to expand inall the directions. As themolecules seek more room,they collide violently withlayers of cool air, and set up agreat air wave that has thesound of thunder.

Why are mornings andevenings less warm than noon?In the mornings andevenings, the rays of the sunfalling on earth are slantingand their distance is more.The earth gets heated up onlyslightly. At noon, the rays ofthe sun falling on the earthare nearly vertical and thedistance is also less, with theresult that the earth getsheated up considerably.Hence mornings and eveni-ngs are less warm than noon.

The sky appears blue. Givereason.Violet and blue light have shortwavelength and are scatteredmore than red light waves.While red light goes almoststraight through the atmos-phere, blue and violet are sca-ttered by particles in the atmo-sphere. Thus we see a blue sky.

What is the differencebetween a planet and a star?Stars are self-luminouscelestial bodies and they have

a system of their own.Planets, on the other hand, arebodies which revolve arounda star and shine by thereflected light of the stars.

What is the differencebetween supersonic andultrasonic sounds?Sounds of frequency higherthan 20,000 Hz are known asultrasonic and are inaudible.The speed greater than thespeed of sound is referred toas supersonic.

Copper wire cannot be usedas a heating element inelectric heaters. Why?Copper has less melting pointand if we use it in electricheater it cannot withstandhigh temperature.

What would happen if theforce of gravity were todisappear suddenly ?In the absence of gravitationalforce, all living objects on theearth will be practically in afloating condition. They willbe thrown away because ofthe centrifugal force causedby the rotation of earth. Aftera certain time the whole earthwill disintegrate.

Radio reception improvesslightly during the night.Why?During day time due tosunlight the radio broadc-asting is affected to a certainextend. Due to the absence ofsun during night radioreception improves slightly.

We perspire on a hot day. why?Human body is physiolo-gically conditioned to main-tain in form the temperature.When the heat produced inthe body becomes excessiveand not dissipated properly,

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the sweat glands inside thebody are stimulated to secretesweat. Therefore, we perspireon a hot day.

The gun kicks back when abullet is fired. Why?According to Newton’s thirdlaw of motion, to every action,there is an equal and oppositereaction. So the gun kicksback when a bullet is fired.

Scientific Instruments& their Uses Accelerometer : An instru-

ment that measures the rateof which the velocity of a bodyis changing.

Altimeter : The instrumentused in aircraft for measuringaltitudes.

Audiophone : Used to impr-ove the imperfect sense ofhearing.

barograph : For continuousrecording of atmosphericpressure.

Binocular : To see the distantobject.

Callipers : An apparatus formeasuring the inside oroutside diameter of bodies.

Chronometer : An instrumentkept on ships for measuringaccurate time.

Carburettor : An apparatusfor charging air with petrolvapours, in an internalcombustion engine.

Clinical thermometer : Formeasuring temperature ofhuman body.

Cardiogram : Instrumentused to trace the movementsof hearts.

Commutator : An instrumentto change or reverse thedirection of an electric current.

Cinematograph : Instrumentused to reflect the image ofpicture on a screen.

Compass needle : For know-ing approximately the north-south direction of a place.

Drinkers apparatus : To helpbreathing in infantileparalysis.

Electro encephalo graph(EEG) : It is a technique ofrecording and interpretingthe electrical activity of brain.Records of the electricalactivity of the brain, ‘brainwaves’ are called electroencephalograms.

Electroscope : To detect thepresence of electric charge.

Eudiometer : It is a glass tubefor measuring volumechanges in chemical reactionsbetween gases.

Galvanometer : For measuringcurrents of small magnitude.

G.M. counter : For detectingthe presence of radiation andcounting certain atomicparticles.

Gravimeter : For recordingmeasurement under waterand to determine thepresence of oil deposits underwater.

Hydrometer : To calculate thespecific gravity of liquids.

Hydrophone : For recordingsound beneath water.

Hygrometer : For measuringhumidity in air.

Lactometer : To find out thepurity of milk.

Magnetometer : To measurethe intensity of earth’smagnetic field.

Microphone : Used to convertsound waves to electricalvibrations.

Microtome : Used to cut anobject into thin parts formicroscopic inspection.

Periscope: It is used usuallyby the crew of a submarine tosurvey the ships etc., on thesurface of the sea while thesubmarine is under water. Italso enables the sailors toobserve objects on the otherside of an obstacle withoutexposing themselves.

Photometer : An apparatusused to compare theilluminative power of twosources of light.

Pyrometer : Thermometersused to measure hightemperature from greatdistance by making use of thelaw of radiation.

Quadrant : For measuringaltitudes and angles innavigation and astronomy.

Quartz clock : A highlyaccurate clock used inastronomical observationsand other precision works.

Refractometer : To measurerefraction indices.

Resistant : Used fordetermining the electricalresistance of conductor.

Saccharimeter : Used fordetermining the amount ofsugar in a solution.

Anemometer : It measures thepower and speed of air.

Audiometer : It measures theintensityof sound.

Hygroscope : An instrumentto measure the height abovesea level.

Internal Combustion engine :It is an engine in which heatsupplied to the workingsubstance is produced bycombustion taking place

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inside the cylinder. eg. petrolengine, dieasel engine.

Odometer : An instrumentused to determine the distancecovered by wheeled vehicles.

Seismograph : An instrumentused to record the intensityand distance of an earth-quake.

Tachometer : An instrumentthat determines speeds ofaeroplanes, motor boats etc.

Telex : It helps in directexchange of informationbetween two countries.

Thermocouple : An instru-ment based on thermoelectricity used for measuringtemperatures.

Ultra sonoscope : It is aninstrument used to determinethe viscosity of liquids.

Venturimeter: It is a devicebased on Bernoulli's theorm,for measuring the quantity ofa liquid flowing through thepipe.

Wireless : It is an instrumentwhich can send messagesfrom one place to anotherwithout the use of wire.

Important Terms Absolute Zero: It is the lowest

temperature theoreticallypossible and is equal to (–273o C).At absolute zero all molecularmotion comes to a stop.

Alternating current : It is anelectric current that perio-dically reverses its directionin the circuit, with a frequencyindependent of the constantsof the circuit.

Boiling point : Boiling pointis the temperature of a liquidat which visible evaporationoccurs throughout the bulk of

the liquid and at which thevapour pressure of the liquidequals the external atmos-pheric pressure. It is thetemperature at which liquidand vapour can exist togetherin equilibrium at a givenpressure.

Centripetal force : The inwardforce that keeps body, suchas a satellite, moving in acircular path. The centripetalforce is directed towards thecentre.

Conduction : It is the processin which heat or electricalenergy is transmitted fromone particle to another nearbyparticles without actualmotion of the particles. Insolids, heat is transmitted byconduction.

Convection : It is a process bywhich heat is transferred byactual motion of the particlesthemselves. In liquid andgases, heat is transmitted byconvection.

Critical Temperature : Thetemperature above which agas cannot be liquefied, nomatter how great a pressureis exerted.

Doppler effect : It is thechange in frequency of a wave(sound or light) due to themotion of the source orobserver. For example, thepitch of a police car sirenappears higher when the carapproaches the listener butlower as the car moves awayfrom listener. It was namedafter the Australian physicist,Christian Doppler (1803-55).

Friction : The force thatopposes the relative motionand produces heat, when twosurfaces are rubbed together.friction is greater between

rough surfaces than betweensmooth or oiled surfaces.

Gamma Rays : They areelectromagnetic radiationsemitted spontaneously bycertain radioactive substan-ces in the process of a nucleartransition.

Horse power (Hp) : It is apractical unit of power whichis equal to 550 foot-poundsper second or 746 watts.

Hydrogen Bomb: Bomb thatworks on the principle ofnuclear fusion. Large scaleexplosion results from thethermonuclear release ofenergy when hydrogen nucleiare fused to form heliumnuclei. The first hydrogenbomb was exploded atEniwetok Atoll in the Pacificocean by the US 1952.

Inertia : It is a property ofmatter by which it resistschange in its state of rest or inits direction of motion.Newton’s first law gives thedefinition for inertia.

Integrated circuit : Anintegrated circuit can bedefined generally as anarrangement of multifunctionsemi conductor devices. Itconsists of a single crystalchip of silicon, nearly 1.5 mmin cross section, containedboth active and passiveelements and their inter-connections.

Kelvin temperature scale : Itis a scale used to measuretemperature. On the kelvinscale absolute zero is 0K, ie.in Kelvin scale 0oC corres-ponds to 273.16 K and 100oCcorresponds to 373.16 K. It isnamed after the BritishScientist, Lord Kelvin.

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Kinetic energy : It is the energypossessed by the body byvirtue of its motion. A movingbullet or a moving stonepossesses kinetic energy.

Latent heat : It is the quantityof heat required to convert aunit amount of a substancefrom one state to anotherwithout changing its tempe-rature. Unit is calories pergram.

Mariner’s Compass : It is adevice for determiningdirection, graduated toindicate 33 directions. The‘‘N’’ point on the dialindicates north pole and the‘‘S’’ point, the south pole. Ithelps the sailors to determinethe North-South direction.

Mirage : It is an opticalillusion often observed indeserts due to total internalreflection and atmosphericrefraction.

Nuclear fission : It is thenuclear reaction in which aheavy atomic nucleus disin-tegrates into nearly two equalfragments releasing a largeamount of energy. Atom bombis based on the principlenuclear fission reaction.

Nuclear fusion : It is a nuclearreaction in which two lightnuclei fuse together to form aheavy nucleus releasing alarge amount of energy.Stellar energy is due to fusionreaction. The principle ofhydrogen bomb is nuclearfusion.

Nuclear reactor : It is anatomic pile in which nuclearchain reaction is controlledfor the production of nuclearenergy. These are wellprotected so that theradiations they emit do not

harm living being. Nuclearreactors are used to produceelectricity.

Potential energy : The energythat an object has because ofits position. An object on ahigh shelf has potentialenergy that is released as itfalls to the ground. Water inan elevated reservoirpossesses potential energy.

Quartz : It is a doublerefracting crystal opticallyuniaxial and positive androtating the plane ofpolarization to the left or rightaccording to the variety, andto a different extent fordifferent colours.

Radioactivity : It is thespontaneous disintegrationof an unstable atomic nucleusaccompanied by the emissionof alpha, beta and gammaradiations. Nucleus having93 or more protons areunstable and is radioactive.

Robot : It is a machine whichcan do a job that is usuallydone by a human being.Robots are used on factoryassembly lines to do oneparticular job that iscontinually repeated.

Surface tension : It is theproperty of a liquid that itssurface behaves like elasticfilm and has a tendency tocontract. This causes smalldroplets to become spherical.Some insects like pond skatercan walk on water becausethe surface tension holdsthem up.

Commutator: It is aninstrument to change orreverse the direction of anelectric current. In dynamo, itis used to convert the

alternating current into directcurrent.

Generator: It is a device bywhich mechanical energy isconverted into electricalenergy. The electrical energyreceived by us from the powerhouse is produced by thegenerator.

Radar: Radio detection andranging employs highfrequency radiowaves fordetecting objects like shipsand aeroplanes. A rotatingaerial sends out pulseswhich are reflected fromobjects on which they fall. Thetime interval betweentransmission and receptionof pulses helps determine thedistance of the object.

Seismograph: An instrumentused for recording theintensity and origin ofearthquake.

Soldering: It is a means ofjoining together two pieces ofmaterial usually metals, bymelting a third metal into thejoint.

Transformer: It is a devicewhich converts low A.C.voltages to high or high A.C.voltages to low. Thetransformer which convertshigh A.C. voltage to low iscalled step-down transfo-rmer. The transformer whichconverts low A.C. voltage tohigh is called step-uptransformer. The transformerworks on the principle ofmutual induction that iselectromagnetic induction.

Chain reaction: It is a seriesof nuclear transformationsinitiated by a single nuclearfission. Chain reaction iscaused by neutrons.