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

Transcription

1 08 00 MT MT - SCIENCE & TECHNOLOGY -I (7) - SEMI PRELIM - I : PAPER - 4 Time : Hours (Model Answer Paper) Max. Marks : 40 A.. (A) Solve the following questions : () If height of orbit of a satellite from earth s surface is increased, the tangential velocity of the satellite will decrease. () Antimony: It is a metalloid and rest are alloys. () False - The escape velocity is responsible to launch a rocket in space which can overcome the earth s gravitational force. Hence, its velocity should be more than the escape velocity. (4) False : Covalent compound have low melting and boiling points (5) The speci c heat capacity of a substance is measured using principle of heat exchange. It states that, Heat lost by hot object Heat gained by cold object. A.. (B) Choose the correct alternative and rewrite the sentences : () Manganese and Magnesium react with dil.hno to evolve hydrogen gas. () The magnetic lines of force are in concentric circles with the wire as the centre, in a plane perpendicular to the conductor. () If the potential difference across a wire is V and the current through the wire is A, the electric power W. (4) Gas evolved during fermentation CO. (5) Ice is a substance which contracts on heating.

2 Q.. Solve the following questions : (Any 5) / MT PAPER 4 () Sodium is a highly reactive metal. (ii) It reacts with the water vapour present in air to form sodium hydroxide and hydrogen. (iii) Hydrogen released catches re in presence of oxygen due to liberation of heat during this reaction. (iv) Sodium does not react with Kerosene and it sinks in it. (v) Thus to prevent sodium from coming in contact with air it is immersed in kerosene. () We can increase the strength of magnetic eld by two ways: Increase the magnitude of current in the circuit (ii) Increase the number of turns of the coil. () - Chlorobutane : Molecular formula C 4 H 9 Cl Structural formula : H H C H H Cl H C C C H H H H (4) During change of state of a substance, object absorbs or rejects heat energy. (ii) But the temperature does not change. (iii) The heat energy is utilized for weakening the bonds between the atoms or molecules in the substance. (iv) Hence, this energy which causes a change in state and does not change the temperature is called Latent heat. (5) Extraction of copper from its sulphide ore. Cu S + O Cu O + SO Copper Oxygen Copper Sulphur sulphide oxide dioxide Cu O + Cu S 6Cu + SO Copper oxide Copper sulphide Copper Sulphur dioxide

3 / MT PAPER 4 (6) Covalent compounds and Ionic compounds : Covalent compounds Ionic compounds These compounds are formed due to sharing of electrons. These compounds are formed due to transfer of electrons. (ii) They exist as solid, liquid and gases. (ii) They exist as solids. (iii) Covalent compounds have low melting and boiling points. (iv) They are generally insoluble in water. (iii) Ionic compounds have high melting and boiling points. (iv) They are mostly soluble in water. (v) They do not conduct electricity in molten or in aqueous solution. (v) They conduct electricity in molten state and in aqueous solution. (7) Fleming s Right Hand Rule : Stretch the thumb, the index nger and the middle nger in such a way that they will be perpendicular to each other. In this position, the thumb indicates the direction of motion of the conductor, the index nger the direction of the magnetic eld, and the middle nger shows the direction of the induced current. Q.. Solve the following questions : (Any 5) () (a) Solenoid : When a copper wire with a resistive coating is wound in a chain of loops (like a spring) it is called solenoid. (ii) When an electric current is passed through a solenoid, magnetic eld is produced in it. (iii) The magnetic lines of force are similar to that of the lines of a bar magnet. (iv) Solenoid has all properties of the eld produced by a bar magnet. (v) One end of the coil acts as a south pole, while the other end as north pole.

4 4 / MT PAPER 4 (b) Magnetic lines of force Solenoid S N Magnetic lines of force of a magnetic eld produced by a current passing through a solenoid coil. Various components are: (a) Copper wire with Resistive coating, (b) Battery (c) Plug key () Given: h 5780 km V.08 km/s M 4 M R 6400 km To nd: T? Formula : V GM, V r T Solution: V GM... GM n G 4M GM n 4 GM GM V Also, r [from ]

5 5 / MT PAPER 4 r r V ( ) 480 s Note: or hrs hrs This taken would be hrs. () (a) AB (b) BC (c) The heat energy absorbed at constant temperature during transformation of liquid into gas is called Latent heat of vapourization. (4) (a) CH -CH -COOH + NaOH CH -CH -COONa + H O Neutralization (b) Na + CH -CH - OH CH -CH -ONa + H All the alcohols react with sodium metal to liberate hydrogen gas and form sodium alkoxide salts. In the reaction of ethanol with sodium metal, hydrogen gas and sodium ethoxide are formed as products. (5) Given: Q A Water/Ice Q B Ammonia (m) kg m (c) kcal/kg C - t 0 C - t 0 C - L 80 kcal/kg 4 kcal/g

6 To nd: m? Formulae: Solution: () Water Water (0 C) Q A Q B Q mc T, Q ml mc T Q A mc T + ml... () () Ammonia Q B m L... () from () and () or Q A Q B ml Water (0 C) Ice (0 C) mc T + ml m L (0-0) + ( 80) m 4 6 / MT PAPER m 4 00 m 4 00 m 4 m kg m g Hence, 586.5g of ammonia has to be evaporated. (6) (a) powdered ore water slits vibrating table concentrated ore Wilfley table method gangue

7 7/ MT PAPER 4 (b) Gangue : Ores contain metal compounds with some of the impurities like soil, sand, rocky substances etc. These impurities are called gangue. (7) A macromolecule formed at regular repetition of a small unit is called polymer. Most of the structure of living things are composed of natural polymers. Polymer Name of the monomer Occurence Polysaccharide Glucose Starch and Cellulose Proteins Alpha amino acids Muscles, hair, enzyme, skin egg. DNA Nucleotide (basedeoxy ribose phosphate) Chromosomes of animals Q.4. Solve the following questions : (Any ) () Electrolytic reduction of alumina : 5 Anode (Graphite) Cathode (Graphite lining) Steel tank Molten aluminium Mixture of alumina, cryolite and fluorspar Outlet for molten aluminium During the process of electrolytic reduction of aluminium, a molten mixture of pure alumina (m.p. is > 000 C) is electrolysed in a steel tank. (ii) This tank is lined inside with carbon which acts as cathode and a set of graphite rods dipped in the molten electrolyte acts as anode. (iii) Cryolite (Na AlF ) and Fluorspar (CaF ) are also added to the 6 mixture to lower the melting point to about 000 C. Current is

8 8 / MT PAPER 4 passed through the electrolyte and aluminium is formed at the cathode. (iv) The molten aluminium sinks to the bottom of the tank as it is heavier from there it is removed periodically. (v) Oxygen is liberated at the anode. (vi) The reaction occuring at the cathode and anode are: Cathode reaction: Al + + e Al(l) (Reduction) Anode reaction: O + 4e O + 4e (Oxidation) (vii) The oxygen liberated reacts with the carbon anode to form carbon dioxide gas. (viii) As a result of this oxidation, carbon anode have to be replaced at intervals. () (a) AC Generator : 5 Magnetic field N B coil C S A D Conducting ring B R R AxleB Carbon brushes Electric generator (b) Principle of working: Electric generators works on the principle of electromagnetic induction. (c) Working: When the armature coil ABCD is rotated by an external force in the magnetic eld provided by strong magnets, it cuts the magnetic lines of forces. Thus, the changing magnetic eld produces induced current in the coil. (ii) After rotation of axle, arm AB moves upwards, while arm CD moves downwards. Therefore, ABCD rotates in the clockwise direction. As per the Fleming s right hand

9 rule, the current is induced in the coil and moves from A B and C D. Current ows in the direction ABCD. (iii) Current ows from B external circuit. to B in the rst half of the revolution in the (iv) After half revolution, arm AB comes to the position of arm CD and arm CD takes the position of arm AB. Due to this, the induced current ows in the direction DCBA. But, arm AB is in contact with B, through slip ring and arm CD is in contact with B. (v) In the second half, in the external circuit, electric current ows from B to B, i.e. opposite to the previous half rotation. (vi) This repeats after every half rotation, and alternating current is produced. This is what is called AC Generator. 9 / MT PAPER 4