TS Physical Science Answer Key SSC 2017

Section – I

1. Ag, Fe, Zn, Na

2. Change the poles of the magnet or wire

3. n = 4, l= 0 , m = 0, s = 1/2

4.  Person develops Myopia. Person can see nearby objects but not distant objects.

5.

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6. We can’t use the same wire as fuse wire. Fuse wire needs to have low melting point in order to break the circuit during overload.

7.

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Section – II

8. Al + Fe2O3 –> Al2O3 + Fe

Aluminium is a more reactive metal. It reduces iron oxide (hematite) to iron.

9.

IMG_20170325_185111Electrons are arranged from lower energy level to higher energy level(Aufbau Principle).

There cannot be more than 2 electrons in an orbital. No two electrons can have all 4 quantum numbers same(Pauli’s Principle)

Degenerate orbitals should be half-filled before pairing up electrons.(Hund’s Rule)

10.

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11. (i) Substance C can be neutral.

(ii) Substance B is basic, with phenolphthalein, it will turn pink in colour

12. Any object(light source) kept at the centre of curvature will give inverted image of the same size (as that of the object) on a screen at the centre of curvature. Place a candle at a certain distance from lens. Adjust the screen such that an inverted same size image is obtained. Now, distance between lens and screen is radius of curvature. Half of the radius will give focal length value.

13. Convex lens: Boy is trying to see moon. When object is at infinity, the image is formed at the focus. As both the lenses have same focal length and are separated by a distance of 2f, the image formed by the first lens, becomes the object for the second lens. Thus, for the second lens, object is at its Focus. The boy would see a highly enlarged image of the moon.


Section – III

14. Chemical Equation

Zn + 2 HCl –> ZnCl2 + H2

In the balanced chemical equation, 2 moles of HCl gives 1 mole of H2. If we use, 1 mole of HCl, we would get 0.5 moles of H2.

At STP,

1 mole of H2 = 6.023×10^23 molecules

Hence, 0.5 moles of H2 = 3.012 x 10^23 molecules

14. Electron Affinity

Definition : Energy released from a neutral gaseous atom when it accepts an electron in its valence shell.

Factors Affecting E.A: Atomic Radius, Effective Nuclear Charge, Screening Effect, Electronic configuration.

Atomic radius: More the atomic radius, lesser is the Electron affinity.

Effective Nuclear Charge is weaker when the valence shell electrons are being located farther away from the nucleus. Lesser the effective nuclear charge, lesser is the electron affinity

Screening Effect is more when there are lots of inner shell electrons. If more inner shells electrons are present, they screen or shield and hence decrease nuclear attraction over valence electrons. More screening effect, less electron affinity.

Electron affinity is lesser if the element has either half-filled electronic configuration and E.A is almost zero if the element has fully-filled  electronic configuration.


15. Hypermetropia and Correction

Person with this defect cannot see nearby objects. 

Near Point – The nearest distance at which the lens can form an image on the retina or the minimum distance beyond which a person with hypermetropia can see an object.

Correction

        • Person with Hypermetropia can see at & beyond Near Point.
        • Person cannot see from 25 cm to Near Point.
        • In order to correct Hypermetropia, we should use a lens that can form the image at or beyond near point for an object located within the near point.
        • Biconvex lens is suited for this purpose.

Calculation

  • object distance, u = -25 cm
  • image distance, v = near point distance, -d
  • Lens Formula:
    • 1/f = 1/v – 1/u
    • 1/f = -1/d – (-1/25)
    • 1/f = -1/d + 1/25
    • 1/f =  -25+d / 25d
    • f = 25d/d-25
    • As, d is more than 25 cm, focal length will be positive value.

15. Current carrying wire in a magnetic field

When a current carrying wire is placed perpendicular to the magnetic field, a mechanical force is exerted on the conductor.

F = q v b sin(theta)

Direction of movement of the conductor is given by Fleming’s Left Hand Rule.

Fore finger, Middle finger and Thumb of the left hand are held at right angles to each other. Fore finger is aligned with the direction of magnetic field, Middle finger points to the direction of current, then the direction in which thumb points, gives the direction of force on the conductor.

Activity:-

  • Suspend a copper wire AB vertically from a support.
  • Lower end B of the wire should touch the surface of mercury kept in a vessel.
  • Positive terminal of a battery is connected to end A of the wire.
  • Circuit is completed by dipping another wire from negative terminal of battery into the mercury vessel
  • The entire set is placed perpendicular to a uniform magnetic field using horse shoe magnet
  • When current passes through the wire from A to B and magnetic field lines are from left to right, then the wire AB moves in the forward direction. Lower end B moves to new position B’, thus in the circuit, connection is broken.
  • Since no current flows in the wire’s new position, mechanical force is not exerted and wire reverts to its original position. Wire makes contact with mercury and current starts to flow in the wire and wire moves forward.
  • This motion is repeated until battery gets drained.
  • If we reverse, the direction of current, then the wire moves in rear direction.

16. Acids/ Bases have ions

Materials Required: HCl, H2SO4, Acetic acid, Citric acid, NaOH, KOH, NH4OH, Glucose, Alcohol, Graphite Rods, AC plug-220V, Bulb, Electrical wires.

Procedure:-

      • Prepare solutions of HCl, H2SO4, Citric acid, Acetic acid,NaOH, KOH, and NH4OH, Glucose, Alcohol.
      • Take a beaker and add HCl solution.
      • Insert 2 Graphite rods into the solution.
      • Connect one of the rod to the AC plug, Connect the other rod to the bulb. Complete the circuit by connecting bulb and AC plug. Use electrical wires for connecting.
      • Switch on the current.
      • Repeat the same procedure for H2SO4, Citric acid, Acetic acid,NaOH, KOH, NH4OH, Glucose and Alcohol

Observation

      • Light bulb glows for all the solutions, except glucose and alcohol.
      • Dim glow is seen for acetic acid and citric acid and NH4OH.
      • Bright glow is seen for HCl and H2SO4, NaOH, KOH.
      • Glucose and alcohol does not have ions, so bulb does not glow.

Inference

      • Acids and Bases behave as electrolytes. Acids give H+ ions in solution which results in flow of current. Bases give OH- ions in solution which results in flow of current.
      • HCl, H2SO4 are strong acids, i.e., more H+ ions are produced.
      • Acetic acid and citric acid are weak acids, i.e., less H+ ions are produced.
      • Similarly, NaOH and KOH are strong bases, giving more OH- ions, whereas, NH4OH is a weak base, giving less OH- ions.

Thus, passing of current and glowing of bulb shows that acids and bases have ions.

16. Esterification

Reaction between carboxylic acid and alcohol in presence of conc.H2SO4 —> esters

Materials Required: Acetic acid, Ethanol, Conc.H2SO4, Beakers, Water, Burner, Test-tube

Procedure

1 ml of ethanol is added to 1 ml of ethanoic acid, few drops of Conc.H2SO4 is added and warmed in water bath for few minutes and then poured into a test tube containing water. The resulting mixture has sweet smell. This is due to the formation of ester

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17. Focal length CalculationNew Doc 2017-03-26 (1)

Metallurgy – Lesson Summary

Class 10

Physical Science

Lesson Summary: Principles of Metallurgy

INTRODUCTION

  • Process of extraction and purification of metals from its ore
  • Earth’s crust is made of minerals. Metals can be extracted from minerals.
  • A mineral from which a metal can be extracted in good yield and in a cost-effective manner is called as Ore.
Ore Name Chemical Formula Ore Type Metal
Bauxite Al2O3.2H2O Oxide ore Al-Aluminium
Pyrolusite MnO2 Oxide ore Mn-Manganese
Hamatite Fe2O3 Oxide ore Fe-Iron
Magnetite Fe3O4 Oxide ore Fe-Iron
Zincite ZnO Oxide ore Zn-Zinc
Zinc Blende ZnS Sulphide ore Zn-Zinc
Cinnabar HgS Sulphide ore Hg-Mercury
Galena PbS Sulphide ore Pb-Lead ore
Epsom MgSO4.7H2O Sulphate ore Mg-Magnesium
Gypsum CaSO4.2H2O Sulphate ore Ca-Calcium
Horn Silver AgCl Chloride ore Ag-Silver
Rock Salt NaCl Chloride ore Na-Sodium
  • Metallurgical Process involves 3 steps
    • Concentration (ore is taken from crust)
    • Extraction (metal is extracted from ore)
    • Refining (pure metal is taken from impure metal)

CONCENTRATION

  • Unwanted rocky materials, dust, soil, sand etc are removed from ore.
  • 4 ways to concentrate an ore
    • Hand-Picking
    • Washing
    • Froth Floatation
    • Magnetic Separation
  • Hand-Picking
    • This method is opted when the impurities have a different texture/size/colour than the ore. Ore particles are hand picked.
  • Washing
    • This method is opted when impurities are smaller/less denser than ore.
    • Ore is kept on an inclined plane surface and washed with water.
    • Impurities are washed with water, leaving the ore concentrated.
  • Froth Floatation
    • This method is used for sulphide ores.
    • Powdered ore is added in a floatation cell containing water and few drops of pine oil.
    • Compressed air is passed into the floatation cell.
    • Ore particles along with froth raise to the top of the cell, while impurities (gangue) settle at the bottom of the cell.
  • Magnetic Separation
    • This method is used for ores that have magnetic property (Eg: iron ore)
    • Powdered ore is passed on a moving belt running across 2 wheels. One of the wheel is magnetic and the other is non magnetic.
    • Magnetic ore particles are attracted towards the magnetic wheel.

EXTRACTION

  • Extraction methods are chosen depending on the reactivity of the metal.
Reactivity Example Method of extraction
Highly Reactive Na, K, Mg, Ca, Al Electrolysis
Moderately Reactive-Sulphate ore and Sulphide ore Fe, Cu, Zn, Pb Roasting + Reduction
Moderately Reactive-Carbonate ore Fe, Cu, Zn, Pb Calcination + Reduction
Less Reactive Ag, Au, Hg Roasting + Reduction

 

  • Extraction of Highly Reactive Metals
  • Electrolysis:-
    • For highly reactive metals, reduction method of extraction is not economically viable.
    • Electrolysis is done with molten (fused) ore. Electrolysis of aqueous solution is not preferable because ions from water will be discharged at the cathode.
    • Process
      • Extraction of Sodium from Rock Salt
      • Cathode: Steel
      • Anode: Graphite
      • Electrolyte: NaCl fused ore
      • On passing electricity, electrolysis occurs.
        • At the Cathode: Sodium ion gets an electron and deposits as Sodium metal
        • At the Anode: Chlorine ions combine to form Chlorine gas. Each Chlorine ion gives off 1 electron.
      • Suitable impurities, if needed, are added to the ore to decrease the melting point.

 

  • Extraction of Moderately Reactive Metals
  • Roasting:-
    • Pyrochemical process
    • Heating sulphide ores in presence of oxygen
    • Metal oxide is obtained

 

 

 

  • Calcination:-
    • Pyrochemical process
    • Heating carbonate ores in the absence of oxygen
    • Metal oxide is obtained

 

 

  • Reduction:-
    • The metal oxides obtained from roasting or calcinations are reduced to their corresponding metals
    • Reduction with carbon
      • Usually done for metals like – Zn, Fe, Ni, Sn, Cu, Pb

 

 

 

 

  • Reduction with other metals
    • More reactive element can reduce a metal oxide by displacing the metal from its oxide.
    • Aluminum – more reactive metal when compared to Zn, Mn, Cr, Fe. Aluminum powder is used as reducing agent.
    • Using Aluminum to reduce metal oxides is a highly exothermic reaction. This reaction is called Thermite reaction, because both Heat and Al2O3 (bauxite) are formed.
    • Thermite reaction
      • A mixture of iron oxide, Fe2O3 and Al powder is heated in presence of Mg ribbon.
      • Al reduces iron oxide to give Fe, Heat and Al2O3. Heat produced is high enough to melt the iron
      • Molten iron, so produced, is used to join railings of tracks or cracked machine parts – thermite welding
    • Auto Reduction
      • Certain sulphide ores (Cu2S) are roasted partially
      • On further heating, Cu2S and Cu2O react together to from metal and SO2

 

 

  • Extraction of Less Reactive Metals
  • Roasting and Reduction by heating
    • Mercury ore (HgS) is heated to from HgO, which on heating is reduced to Hg

 

 

  • Treating with KCN
    • Silver sulphide is treated with KCN to form potassium silver cyanide. When Zinc dust is added to potassium silver cyanide, it gives Ag

 

PURIFICATION

  • Metals obtained from extraction process contain some impurities. Refining of impure metals is called Purification
  • Distillation
    • Purification of low boiling metals – Zn, Hg
    • Impurities – High boiling
    • Extracted metal is distilled to obtain pure metal
  • Liquation
    • Purification of metals with low melting point– Sn
    • Impurities – High boiling
    • Extracted are metals are heated and pure metal is collected from a sloppy surface
  • Poling
    • Molten metal is stirred with poles of wood
    • On heating, impurities get converted to gases or get oxidized and form as removable slag over the molten metal.
  • Electrolytic Refining
    • Usually done for metals like Cu, Zn, Sn, Pb, Cr, Ni, Ag, Au
    • Thick block of impure metal = Anode
    • Thin strip of pure metal = Cathode
    • Aqueous solution of the corresponding metal salt = Electrolyte
    • On passing electric current, metal from anode goes into solution, metal from electrolyte deposits at cathode
    • Soluble impurities from anode goes into solution, insoluble impurities from anode, deposit at the bottom of the anode. This is called anode mud.
    • Anode mud contains valuable metals like Sb, Te, Se, Ag, Au
    • Electrolytic Refining of Copper
      • Acidified Copper sulphate solution, i.e., CuSO4 + H2SO4 + H2O = electrolyte
      • Impure copper metal = Anode, i,e., connected to positive terminal of battery
      • Pure copper metal = Cathode , i,e., connected to negative terminal of battery
      • On passing electric current, impure Cu from anode goes into CuSO4 solution, pure Cu2+ from CuSO4 gets deposited at cathode as Cu
      • As the process goes on, anode thickness decreases and anode thickness increases. Pure copper is obtained at the cathode.
      • Cathode reaction

 

  • Anode reaction

 

CORROSION

  • Reactive metals like copper, iron, silver gets oxidized in the presence of moisture and O2
  • Reddish brown dust –Hydrated Iron oxide; Green coating on copper – Copper carbonate; Blackening of silver – Silver sulphide
  • Corrosion of iron is rusting
    • Rusting occurs in the presence of both moisture and O2
      • When iron nail is kept in a test tube with water and oil = no rusting
      • When iron nail is kept in a test tube with dry air and dry CaCl2 = no rusting
      • When iron nail is kept in a test tube with water and air = rusting
    • Corrosion is an electrochemical process
      • Anode = where oxidation of Fe occurs

 

  • Cathode = reduction of oxygen occurs in the presence of H+ ion. This is done by the electrons released from anode

 

 

  • Overall Reaction

 

  • Fe2+ is further oxidized to Fe3+ which forms hydrated iron oxide

 

  • Prevention of Corrosion
    • By painting
    • By applying grease or oil
    • By galvanization – electroplating zinc on iron objects.
    • By tin or chromium plating
    • By alloying
      • Alloy is a homogenous mixture of two or more metals.
      • Iron is alloyed with Cr and Ni to obtain stainless steel.
      • Alloys are generally stronger than the metals from which they are made; more resistant to corrosion; have lower electrical conductivity than pure metals and improved properties than pure metals.
      • Other common alloys
        • Gold + Silver or copper = 22 carat gold
        • Copper + Zinc = Brass
        • Mercury + other metals = Amalgam

OTHER PROCESSES

  • Smelting
    • Ore is mixed with flux and fuel and heated strongly
    • Flux is a substance added to remove impurities (gangue) from ore.
    • If gangue is acidic, flux is basic and vice versa
    • During smelting, gangue and flux react to form a removable substance called slag

 

 

 

 

 

 

 

 

 

  • Furnace
    • Pyrochemical process is carried out in furnace.
    • Furnace has 3 parts – Hearth, Chimney, Fire Box
    • Ore is kept at hearth of the furnace
    • Fuel is kept in fire box
    • Waste or gases go out of the chimney
    • Types of furnace – Reverberatory furnace, Blast furnace, Retort furnace
    • Blast furnace
      • Fire box an hearth are combined in a big chamber
      • Haematite ore is smelted in blast furnace
    • Reverberatory furnace
      • Fire box an hearth are kept in separate chambers
      • Vapours from the burning fuel touch the ore and heat it.
    • Retort furnace
      • Fire box an hearth are kept in separate chambers
      • Flames of the fuel do not touch the ore.

Question List-Human Eye and Colourful World

Hello again,

This is a question list for 5th lesson- Human Eye and Colorful World, Physical Science text-book. Happy Solving.

                                         WORKSHEET

                  TOPIC: HUMAN EYE AND COLOURFUL WORLD

SHORT Q & A (2 OR 1 MARKS)

  1. What is least distance of distinct vision?
  2. What is the angle of vision?
  3. How do you appreciate the role of ciliary muscles?
  4. What is the role of iris?
  5. How does iris help the pupil as a variable aperture?
  6. What are ‘rods’ and ‘cones’?
  7. Calculate the minimal focal length of eye.
  8. Calculate the maximum focal length of eye.
  9. What is accommodation of lens?
  10. What do you understand by far-point?
  11. What do you understand by near-point?
  12. How do you correct the following defects-
    1. Myopia
    2. Hypermetropia
    3. Presbyopia
  13. Define Power of Lens. Write its unit.
  14. Find the focal length of a lens of power, -2 D. What type of lens is this?
  15. A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?
  16. A student has difficulty in reading the blackboard while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?
  17. What is a prism?
  18. Show refraction of a light ray through a prism.
  19. Through a model graph show the variation between angle of incidence and angle of deviation.
  20. Light of wavelength  L1 enters a medium with refractive index n2 from a medium with refractive index n1. What is the wavelength of light in second medium?
  21. Write an expression for finding the refractive index of glass prism.
  22. What is dispersion of light?
  23. Through a diagram, show refraction and dispersion of light in a water drop.
  24. What is scattering of light?
  25. A light of wavelength 500nm travels in air. Find its frequency.
  26. What is scattering centre?
  27. Why is sky blue in colour?
  28. Why does sky appear white during noon time?
  29. Why does sky appear red or orange in colour during sunrise and sunset?
  30. What is Raman Effect? How is it used in identifying molecules?
  31. Why does rainbow appear like a “bow”?
  32. When do we observe a rainbow?
  33. Draw a structure of human eye and label parts.
  34. Anitha can only see objects beyond 50 cm from her eyes. Which lens is preferable to correct her vision. What should be its power?
  35. Which colour has the shortest wavelength?
  36. Which colour has the smallest frequency?
  37. Write a relation between frequency and wavelength of light.
  38. What happens to your eye when you enter a darkened cinema hall from bright sunshine? (or) Why does it take some time to see objects in dim room when you enter the room from bright sunshine outside?
  39. Explain the functions of the following parts of the eye
    1. Cornea
    2. Pupil
    3. Retina
    4. Optic nerve
  40. Consider the following 2 situations. The eyes of a person are focused on
    1.  on a nearby object
    2. on a distant object.

In which case, the focal length of eye-lens will be maximum? In which case, the converging power of eye-lens will be maximum?

 

4 MARKS Q & A

  1. Discuss the structure of eye briefly.
  2. Explain how accommodation of eye lens is vital for us to visualize the world.
  3. What is short-sight?  Discuss this accommodation defect in detail. How to rectify this defect? Draw Diagrams.
  4. What is long-sight?  Discuss this accommodation defect in detail. How to rectify this defect? Draw Diagrams.
  5. What is Presbyopia? How to rectify this eye defect.
  6. How would you find the refractive index of a prism experimentally.
  7. Derive an expression for finding the refractive index of a prism.
  8. Discuss the formation of rainbow.
  9. Discuss briefly on scattering of light?
  10. Through an experiment, explain how particle size affects scattering of light.

 

Questions-Human Eye