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1 08 00 MT MT - SCIENCE & TECHNOLOGY - I (7) - SEMI PRELIM - II : PAPER - 6 Time : Hours (Model Answer Paper) Max. Marks : 40 A.. (A) Solve the following questions : () In the dispersion of sunlight through glass prism the violet light deviates the most. () Unbalanced equation () False - If the separation between two particles is doubled, the gravitational force between the particles becomes 4 (4) False - Group 7 elements are known as Halogens. (5) Match the following : Column A Column B the initial force. () Presbyopia (c) Convex lens () Colour blindness (a) Cone cells A.. (B) Choose the correct alternative and rewrite the sentences : () Hydrogen () When a ray of light travels from air to glass and strikes the surface of separation at 90, then it passes without bending. () A glass slab is placed in the path of convergent light. The point of convergence of light moves away from the slab. (4) Alkaline earth metals have valency. This means that their position in the Modern Periodic table is in Group. (5) To obtain an image of the same size as the object object with the help of a convex lens, the object should be placed at F. A.. Solve the following questions : (Any 5) () Silver nitrate reacts with sodium chloride to form a precipitate of silver chloride and solution of sodium nitrate. AgNO (aq) + NaCl (aq) AgCl + NaNO (aq) Silver Nitrate Sodium Chloride Silver Chloride Sodium Nitrate

2 / MT PAPER 6 () Given: Power of lens (P) =.5 D To nd: Focal length (f) =? Formula: P = f (m) Solution: P = f (m) f = P f = f = f = = 0.67 m Since f is +ve, lens used is convex. Hence defect is Hypermetropia (farsightedness) () s-block elements and p-block elements : s-block elements (i) Elements in group and are called s-block elements including hydrogen. (ii) They contain or electrons in the outermost shell. (iii) They are all metals (except hydrogen). (4) (i) Persistence of vision p-block elements (i) Elements in group to 7 and zero group are called p-block elements. (ii) They contain to 8 electrons in the outermost shell. (iii) They are metals, nonmetals and metalloids. The impression of the image lasts on the retina for th of a second 6 after the object is removed; during this time if any other image is formed on the retina then we feel continuity in the images. This is known as persistence of vision.

3 / MT PAPER 6 (ii) Distance of distinct vision : The minimum distance from the normal eye, at which the objects can be seen clearly and distinctly without any strain to the eye is known as the distance of distinct vision. (5) (i) The grills of doors and windows are generally made of the metal iron. (ii) When they are exposed to air, due to the effect of moisture in air, iron undergoes slow oxidation reaction and forms a layer of reddish brown rust which gets deposited on the surface of grills. (iii) Thus due to the reaction of slow process of decay or destruction of metal iron, the grills of doors and windows made of metal iron get corroded. (iv) Hence, in order to prevent the rust and corrosion, grills of doors and windows are always painted before they are used. (v) By doing this, air and moisture cannot come in contact with the iron and hence rusting doesn t take place.: (6) Name of the element Atomic Number Lithium (Li) Electronic Con guration K L M Silicon (Si) Helium (He) Sodium (Na) 8 Phosphorous (P) As the elements Silicon (Si), Sodium (Na) and Phosphorous (P) have electrons in the three shells; K, L and M, therefore these elements belong to period as the number of shells indicates the period number. (7) As we gradually go towards the centre of the Earth, the mass of Earth under consideration goes on decreasing. We know, g = GM R At the centre of the Earth, the mass of earth under consideration is zero; Hence,g at the centre of the earth becomes zero. A.. Solve the following questions : (Any 5) () (i) If a planet revolves around the Sun in a circular orbit, then the centripetal force exerted on it by the Sun is F = mv r

4 where, m - mass of the planet v - velocity and r - radius of its orbit. 4 / MT PAPER 6 (ii) Distance travelled in one revolution by the planet = Circumference Time period of revolution = (T) speed = distance time v = πr T F = mv r m πr T F = r F = 4mπ r T F = 4mπ r T F = 4mπ r F = but r r r T... 4mπ kr 4mπ k is constant T r = k or r T...(i)...[from(i)] = k...(ii)...[from(ii)] = r F r This is how Newton proved the inverse square law of gravity using Kepler s laws. () Given: Displacement (s) = 4.05 m g = -0 m/s Final velocity (v) = 0 m/s To nd: Initial velocity (u) =? t total (t) =? Formulae: v = u + gs, v = u + gt t total = t Solution: v = u + gs

5 0 = u + (-0) = u - 8 u = 8 u = 9 m/s v = u + gt 0 = 9 + (-0) t 0 t = 9 t = 0.9 s Time of ascent = Time of descent t total = t = 0.9 =.8 s The initial velocity was 9 m/s and total time taken to come down, is.8 s. 5 / MT PAPER 6 () (i) An iris in human eye controls and regulates the amount of light entering the eye and imparts colour to the eye. (ii) Far-sightedness and Near-sightedness : (i) Far-sightedness Curvature of cornea and eyelens decreases (i) Near-sightedness Curvature of cornea and eyelens increases (ii) Eyeball attens slightly (ii) Eyeball elongates slightly (iii) Image of the nearby object falls behind the retina. (iv) Image of the distant object falls on the retina. (v) This defect is corrected by using a spectacle of convex lens of suitable focal length. (iii) Image of the nearby object falls on the retina. (iv) Image of the distant object falls in front of the retina. (v) This defect is corrected by using a spectacle of concave lens of suitable focal length. (4) (i) The slow process of decay or destruction of metal due to the effect of air, moisture and acids on it is known as corrosion. (ii) Gold ornaments do not get corroded. (iii) Gold is a noble metal and is least reactive. (iv) It does not react with water or any of the gases present in the atmosphere. Common acids do not have any effect on gold. (v) Thus, gold ornaments do not corrode.

6 6 / MT PAPER 6 (5) (a) Mirage (b) Refraction of light or Total Internal Re ection. (c) Formation of Rainbow (6) Reduction Reaction : The chemical reaction in which reactants gain hydrogen or loses oxygen to form product is called reduction reactions. For example : () HgO (s) Hg (l) + O (g) Mercuric Mercury Oxygen oxide () H (g) + Cl (g) HCl (l) Hydrogen Chlorine Hydrogen Chloride (7) (i) The Modern Periodic Table was classi ed on the basis of atomic number. All isotopes of the same elements have different masses but same atomic number. Therefore, they occupy the same position in the Modern Periodic table. (ii) When elements are arranged according to their atomic numbers, the anomaly regarding certain pairs of elements in Mendeleev s Periodic Table disappears eg. atomic number of cobalt and nickel are 7 and 8 respectively. Therefore, cobalt will come rst and then nickel, although atomic mass of cobalt is greater. (iii) Elements are classi ed according to their electronic con guration into different blocks. A.4. Solve the following questions : (Any ) () (a) Step : Write the equation given. NaOH + H Na + H O...() Count the number of atoms of each element in product and reactants. Elements reactants products Na O 5 5 H S The number of oxygen and sulphur atoms are equal on both sides. Hence, we will balance Na atoms on both sides.

7 7 / MT PAPER 6 Step : To balance Na atom we write coef cient for NaOH. NaOH + H Na + H O...() Step : Count the number of Na atoms, H atoms, O atoms and S atoms on both sides. Elements reactants products Na O 6 5 H 4 S Step 4: To balance H we write coef cient for H O on the product side. Hence the equation becomes. NaOH + H Na + H O...() Again count the number of atoms of elements on both sides. Elements reactants products Na O 6 6 H 4 4 S Now the number of atoms of each elements are equal on both sides. Hence, equation () is a balanced equation. (b) The rate of reaction depends upon the following factors. (i) Nature of the reactants: (a) NO + O NO Fast (g) (g) (g) CO (g) + O (g) CO (g) Slow These reactions appear to be similar but the rst is fast while second is slow. This is due to the difference in the amounts of energies which are required for breaking up of different bonds and different amounts of energies are released in the formation of different bonds. (b) Al + 6HCl AlCl + H Zn + HCl ZnCl + H On reaction of both Al and Zn with dilute hydrochloric acid H gas is liberated and water soluble salts of there metals are formed. However the reaction of aluminium metal takes place faster as compared to zinc metal. The nature of metal is responsible for

8 8 / MT PAPER 6 this difference. Al is more reactive than Zn. Therefore the rate of reaction of Al with hydrochloric acid is higher than that of zinc. Nature of reactivity of reactants in uences the rate of a chemical reaction. (ii) Concentration of the reactants: Greater the concentration of the reactants, faster is the reactions conversely, as the concentrations of the reactants decreases the rate of reaction also decreases. Dilute HCl reacts slowly with CaCO and thereby CaCO disappears slowly and CO also liberate slowly. On the other hand the reaction with concentrated HCl takes place rapidly and CaCO disappears fast. Concentrated acid reacts faster than dilute acid, which means that rate of reaction is proportional to the concentration of reactants. (iii) Temperature: The rate of reaction increases with increases of temperature. In most of the cases, the rate of reaction becomes nearly double for 0k rise of temperature. In some cases, reactions do not take place at room temperature but take place at higher temperature. (iv) Presence of catalyst: A catalyst generally increases the speed of a reaction without itself being consumed in the reaction. In case of reverse reactions, a catalyst helps to attain the equilibrium quickly without disturbing the state of equilibrium. (v) Size of the particles of reactants: For a reaction involving a solid reactant or catalyst, the smaller is the particle size, greater is the surface area, and the faster is the reaction. (vi) Presence of light: Some reactions do not take place in the dark but can take place in the presence of light like photosynthesis or photochemical reactions. () (a) (i) The minimum distance at which an object is placed from the normal eye so that it can be seen clearly without giving any strain on the eye is called the distance of the distinct vision. (ii) This distance is 5 cm for a normal human eye. (iii) If the object is placed at a distance less than 5 cm, ciliary muscles are unable to adjust the lens, there is a strain on the eye and it cannot be seen clearly. (iv) Hence an object should be placed at 5 cm or more to have a clear and sharp image of it on the retina. 5

9 9 / MT PAPER 6 (b) (i) Object u F e u F o Objective lens Eyepiece Image (ii) A is objective lens and B is Eyepiece lens.

Time : 2 Hours (Model Answer Paper) Max. Marks : 40

Time : 2 Hours (Model Answer Paper) Max. Marks : 40 08 00 MT MT - SCIENCE & TECHNOLOGY - I (7) - SEMI PRELIM - II : PAPER - 4 Time : Hours (Model Answer Paper) Max. Marks : 40 A.. (A) Solve the following questions : () The focal length of a convex lens