light

1.            What is dispersion? How is it caused?

a)      The phenomenon of splitting or separation of composite light into its constituent colors is called dispersion.

b)      It is caused due to the difference in the frequency or wavelength of the constituent colors

2.            Mention the range of wavelength of visible spectrum?

                The wavelength of visible spectrum ranges from 400nm to 700nm.

3.            What is meant by a pure spectrum?

                A pure spectrum is a spectrum in which the constituent colours occupy their respective positions and are distinct.

4.            What is a spectroscope?

                A spectroscope is an instrument used to obtain pure spectrum of a composite light using a prism.

5.            Mention the different parts of a spectroscope?

                Collimator, telescope, prsim and prism table are the different parts of a spectroscope.

6.            List three uses of spectroscope?

                Spectroscope is used:

·         To study the elements present in the sun

·         To identify the elements present in the solar atmosphere

·         In spectrochemical analysis in industries, medicine and crime detection

7.            What is a continuous spectrum?

                A rainbow like spectrum obtained from sunlight, light from a filament of a lamp, molten iron or a candle is called a                 continuous emission spectrum.

8.            What is a line emission spectrum?

·         The spectrum formed when gases of vapors are made to emit light is called line emission spectrum.

·         It consists of a number of sharp, bright colored lines against a dark background.

·         These lines are the slit images of different colors.

9              What are Fraunhoffer lines?

·         When white light from a carbon lamp is passed through sodium vapor, then the continuous spectrum will have two dark lines in the yellow region.

·         Similarly the solar spectrum will have several dark lines in its spectrum.

·         These are called Fraunhoffer lines.

10.          Explain Raman Effect?

·         When a beam of monochromatic light was passed through an organic liquid such as benzene or toluene, the resulting scattered light was polychromatic and not monochromatic as the incident light.

·         The scattered light contained higher and lower frequencies in addition to the incident light.

·         This phenomenon is called Raman Effect.

11.          What is the important difference between Raman scattering and Rayleigh scattering?

                Rayleigh scattering is coherent scattering, while Raman scattering is incoherent scattering

12.          Mention one application of Raman Effect.

                Raman Effect is useful to understand the structure of molecules that constitute matter.

OTHER IMPORTANT QUESTIONS

1.            What is a spectrum?

                The band of colours (wavelengths) obtained by dispersion of a narrow beam of composite light is called spectrum

2.            State Rayleigh’s principle on dispersion.

                According to the principle, the intensity of scattered light is inversely proportional to the fourth power of the                 wavelength.

3.            Name the scientist who predicted the theoretical background for it.

                Smekal predicted the theoretical background for Raman Effect.

water

1.            List the physical properties of water?

                Water is a colourless, tasteless and odourless liquid.

2.            Why is water called a universal solvent?

                Water can dissolve maximum number of solvents in it and hence is called a universal solvent.

3.            Mention any six substances that are insoluble in water?

                Sand, glass, wood, plastic, stone, metals, paper

4.            List any four substances that are soluble in water?

                Salt, sugar, bicarbonates

5.            Why do certain samples of water not readily give lather with soap?

                These samples contain soluble salts like carbonates and bicarbonates of magnesium and calcium that cause                 hardness in water and hence does not give lather with soap.

6.            What is soft water?

                Water that give lather easily with ordinary soap is called soft water.

1.            What is the nature of water that comes out of the permutit?

                The water that comes out of the permutit is soft, but not pure.

2.            Mention any two properties of pure water?

                Pure water is colourless and tasteless.

3.            How does water get its color, taste and odour?

                Water gets its colour, taste and odour by the impurities present in it.

4.            How is water classified? What is the basis for this classification?

                Water is classified as hard water and soft water based on the changes observes during its reaction with soap.

5.            What do you mean by conservation of water?

                The effort made by the society towards the rational use, prevention of pollution and recycling of water is called                 water conservation.

6.            Why should we soften hard water before it is used?

·         Hard water is not suitable for washing as there will be heavy wastage of soap and clothes are not washed properly and leave a yellow stain on the clothes.

·         Hard water consumes more fuel for cooking and the salts accumulate on the inner walls of the vessels making their cleaning difficult.

·         In industries, where boilers are used, it leaves a scale on the inner walls of the boiler and sometimes even causes foaming and explosion.

·         Hard water forms scales inside the pipes and corrodes the pipes

                Hence we should soften hard water before it is used.

7.            What is permutit? Mention two methods of preparing it?

·         Artificially prepared sodium aluminium silicate is called permutit.

·         It is prepared by heating quartz, sand, china clay and sodium carbonate.

·         It can also be prepared by fusing sodium silicate and sodium aluminate.

8. Name the simplest method of removing permanent hardness of water. On what principle does it work?

·         Distillation is the simplest methods of removing permanent hardness of water.

·         The condensation of water vapors produced is the principle involved in the process.

9. Mention two advantages and two disadvantages of permutit process of softening hard water?

a)      Advantages:

·         It is economical

·         It removes hardness more or less completely.

b)      Disadvantages:

·         It is not suitable, if water contains suspended impurities and sodium salts.

·         It does not remove lead, iron or manganese if present as impurities.

10  Describe briefly the two types of hardness in water?

·         Based on the negative ions present along with magnesium and calcium ions, hard water is grouped as temporary hard water and permanent hard water.

·         Water that contain bicarbonate ions along with magnesium and calcium ions and that can be softened by boiling is called temporary hard water.

·         Water that contains chloride and sulphate ions along with magnesium and calcium ions is called permanent hard water.

·         When all the ions are precipitated, water begins to give lather.

11.What is hard water? Describe briefly the soda process of removing hardness in water?

·         Water that forms an insoluble scum with soap before giving lather is called hard water.

·         Sodium carbonate is added to the hard water. It reacts with the salts that cause hardness and gives their respective carbonates that are insoluble. These insoluble carbonates are removed by filtration.

Universe

1.            Name the nearest star to the earth?

                Sun is the nearest star to the earth

2.            Light from the sun reaches the earth in 8.3 minutes. Calculate the distance of the sun from

                 the earth?

                (Velocity of light = 3 x 10⁵kms^-1)

                Velocity = distance traveled/time taken or distance traveled = velocity x time taken

                Distance travelled = 3 x 10⁸ x 100 x 8.3 x 60 = 1.5 x 10⁸km

3.            What is solar luminosity? What is its value?

a         )      The amount of solar energy radiated per second in all direction is called solar luminosity.

b        )      Its value is 3.9 x 10²⁶

4.            What is the surface temperature of the sun?

                The surface temperature of the sun is about 6000K

7.            Give the relation between Parsec and light year?

                1 Parsec = 3.26 light year

8.            Name the scale on which the brightness of a body is represented?

                The brightness of a body is represented on magnitude scale.

9.            Two stars have a magnitude difference 6. What is their brightness ratio?

                Their brightness ratio is 1:100

10.          Define luminosity of a star. On what factors does it depend?

a)      The total energy emitted by a star in one second is called its luminosity.

b)      The luminosity of a star depends on the temperature and diameter of the star.

11.          Name the characteristics on which the size of a star is determined?

                The size of a star is determined based on their temperature and luminosity

12.          What is a galaxy?

                A huge group of stars held together by gravitation is called a galaxy

13.          Mention the different types of galaxies?

                Spiral, irregular and elliptical are the three types of galaxies.

14.          Explain the stages of evolution of a sun like star?

                Following are the major stages in the evolution of a star.

                Protostar

The star begins its life with a huge cloud of gaseous hydrogen that contract due to gravity. This results in increased pressure and density and forms a spherical mass at the canter of the cloud and is called the protostar.

Steady state

When the star contracts, it reaches millions of degrees and the fusion of hydrogen nucleus begins. The energy released during the nuclear fusion expands the matter and balances the inward gravitational pull. This stage is called the steady state.

                Red giant

Due to the continuous fusion of hydrogen into helium a core of helium is formed. the envelope expands and cools into a red star and is called the red giant.

                White dwarf

As a star’s envelope expands its core contracts and heats up and reaches a temperature of around 10⁸K. Helium is converted in to carbon. When there is no more fusion, the core cannot contract further and the outer envelope gets detached and thrown into space. The core collapses under the action of gravity.

As the temperature increases, the core develops pressure which prevents further collapse and becomes a white dwarf and shines due to its high temperature.

When it slowly cools, it becomes dimmer and becomes a black dwarf.

15.          Explain briefly the life cycle of a massive star after its red giant stage?

·         After the red giant stage, due to the fusion of helium, a carbon core is produced.

·         This ignites to produce a core of oxygen, magnesium, silicon, iron etc, each inside the layer of another with iron as the inner most core.

·         At this stage, the star explodes and is called the supernova.

·         During supernova, most of the material is thrown out at a great speed of about 10⁴ km/second, leaving behind a sphere of neutrons. This is called the neutron star.

·         Initially it looks like a nebula and gradually mixes with the gaseous clouds to form new stars.

·         The stars thus formed will have elements heavier than hydrogen and helium.

16.          What is the difference between open and globular star clusters?

·         In the open type of star clusters stars appear to be loosely bound and have many blue young stars

·         In globular type, stars appear to be tightly bound and have mostly red colour stars.

17.          What is the evidence for expanding universe?

·         The spectral lines of all galaxies show red shift

·         The spectral lines of a given galaxy show equal red shift.

·         These red shifts show that the galaxies are moving away from us with enormous speeds.

·         This shows that the universe is expanding.

18.          State Hubble’s law. On what basis is it derived?

a)      Hubble’s law states that the velocity of recession of a celestial body is proportional to its distance from us.

b)      It is based on the study of red shift of the various galaxies.

19.          Write a note on Big Bang theory?

·         Big Bang theory refers to the explosion of the primordial fireball with a big bang.

·         This resulted in the expansion of the universe

·         As a result of big bang, matter and radiation cooled, stars and galaxies were formed.

·         Planets came into existence and life came into e1.            Name the theory that can be used to determine the mass of the earth?

                Kepler’s laws of planetary motion can be used to determine the mass of the earth.

2.            Where do you find solar telescopes in India?

                Solar telescopes are found at Kodaikanal and Udaipur.

3.            How do you know the existence of different elements in the sun?

·         Solar spectrum has different Fraunhofer lines as seen from a spectroscope.

·         An analysis of these reveals the existence of different elements in the sun.

4.            What is photosphere?

                The visible disc of the sun is called the photosphere

5.            Describe briefly the structure of corona?

·         The region beyond the chromospheres of the sun is called corona.

·         It extends to millions of km.

·         During a total solar eclipse, it is seen as a white halo around the sun.

·         When it is covered by the photosphere and chromospheres, matter in this region is plasma.

6.            What are granulations and spicules?

                The grain like patterns and thread like structures seen on the photosphere of the sun are called granulations and                 spicules respectively.

7.            What are solar flares?

                Matter steaming out of the sun’s surface like thunderstorms is called solar flares.

8.            What are solar prominences?

                Matter streaming out of the sun’s surface burst like thunderstorm and looping back into the photosphere are                 called solar prominences.

9.            What are aurora?

                The spectacular color display of charged particles ejected at great speeds from the sun when they ionize the air                 molecules are called aurora.

10.          How are we protected from many electromagnetic radiations from the sun?

                The earth’s atmosphere absorbs many of the electromagnetic radiations like ultraviolet rays, X-rays etc. and allows                 only heat, light and radio waves and a small amount of ultraviolet rays. Hence we are protected.

11.          What makes the sun highly energetic?

                The temperature at the core of the sun that is of an order of 20 million Kelvin and the nuclear reactions taking                 place there makes the sun highly energetic.

12.          How does energy from the sun reaches the photosphere?

                Energy from the sun reaches the photosphere through radiation and convection.

13.          Why do stars differ in their color?

                Stars differ in their color due to the difference in their temperature.