Tuesday, July 30, 2013

10th (X) Science solved Paper SA Term-1 (Sep)

Q.1. What changes in the colour of iron nails and copper sulphate solution do you observe after keeping the iron nails dipped in copper sulphate solution for about 30 minutes?
Ans: Iron nails get coated with a reddish brown substance. Copper sulphate solution becomes light green
Q.2. A charged particle enters at right angles into a uniform magnetic field. What should be the nature of charge on the particle if it begins to move in a direction pointing vertically out of the page due to its interaction with the magnetic field ?
Ans: Positive charge / Proton
Q.3. What happens when an aqueous solution of sodium sulphate reacts with an aqueous solution of barium chloride? State the physical conditions of reactants in which the reaction between them will not take place. Write the balanced chemical equation for the reaction and name the type of reaction.
Ans: (i) A white precipitate / Insoluble substance is formed.
(ii) If the reactants are in solid state.  (iii) Na2SO4 + BaCl2 à 2 NaCl + BaSO4  
(iv) Double displacement / Double decomposition / Precipitation
Q.4. What is the main constituent of biogas ? How is biogas obtained from biomass ? Write any two advantages of using this gas.
 Ans: (i) Methane / CH4  (ii) By anaerobic decomposition of biomass in the presence of    microorganisms. (iii) It is a clean fuel.  It burns without smoke. It leaves no residue.Its  heat capacity / calorific value is high. It is used for lighting purpose. Safe and efficient  method of waste disposal.slurry left behind can be used as an excellent manure. (Any   two)
Q.5. What is a solenoid ? Draw the pattern of magnetic field lines of a solenoid through which a steady current flows. What does the pattern of field lines inside the solenoid indicate ?
Ans: Solenoid is a coil of many circular turns of insulated copper wire wrapped closely in  the shape of a cylinder.
Draw diagram:
Pattern indicates that the magnetic field is uniform at all points inside the solenoid.
Q.6.  A coil of insulated wire is connected to a galvanometer. What would be seen if a bar magnet with its north pole towards one face of the coil is moved quickly towards it,   moved quickly away from the coil and placed near its one face ? Name the phenomenon involved
 Ans: (i) Momentary deflection in the galvanometer to one side.
 (ii) Momentary deflection   in the galvanometer, now in the opposite direction. (iii) No deflection in the galvanometer.    Phenomenon involved is electromagnetic induction.
Q.7. Mention any four limitations in harnessing wind energy on a large scale.
Ans: Any four of the following :
(i) It can be used only at those places where wind blows for the greater part of the year.
(ii) Wind speed should be higher than 15 km/h to rotate the turbine at the required speed.
(iii) Need of a back up facility when there is no wind.
(iv) Requires large area for setting up wind energy farms.
(v) Tower and blades require a high level of maintenance.
Q.8. No chemical reaction takes place when granules of a solid, A, are mixed with the powder of another solid, B. However when the mixture is heated, a reaction takes place between its components. One of the products, C, is a metal and settles down in the molten state while the other product, D, floats over it. It was observed that the reaction is highly exothermic.
Based on the given information make an assumption about A and B and write a chemical equation for the chemical reaction indicating the conditions of reaction, physical state of reactants and products and thermal status of the reaction.
Mention any two types of reactions under which above chemical reaction can be classified.
Ans: A : Fe2O3 ; B : Al
(i) Fe2O3(s) + 2 Al (s)  ---Heat-à 2 Fe (l) + Al2O3(s) + heat
condition of the reaction, physical state of reactants and products,thermal status.
(ii) Displacement Reaction ,Redox Reaction,Exothermic Reaction
Q.9. What is meant by refining of a metals ? Name the most widely used method of refining impure metals produced by various reduction processes. Describe with the help of a labelled diagram how this method may be used for refining of copper.
Ans: Removal of impurities from a crude metal is called refining of metals.
Description :
On passing the current through the electrolyte, the pure metal from the anode dissolves into the electrolyte. An equivalent amount of pure metal from the electrolyte is deposited on the cathode. The soluble impurities go into the solution, whereas, the insoluble impurities settle down at the bottom of the anode and are known as anode mud.
Q.10. Derive the expression for the heat produced due to a current ‘I’ flowing for a time interval ‘t’ through a resistor ‘R’ having a potential difference ‘V’ across its ends. With which name is the relation known ? How much heat will an instrument of 12W produce in one minute if it is connected to a battery of 12V ?
Ans: (i) Work done in moving the charge W = VQ
Power input, P =(VQ)/t = V I
Energy, E = P × t = V I t
This energy gets dissipated in the form of heat. H = V I t
Applying Ohm's law, we get  H = I2Rt 2
(ii) The relation is known as Joule's law of heating.
(iii) P = 12 W t = 1 minute = 60s
H = P × t = 12 W × 60s
H = 720 J
1. What change in colour is observed when white silver chloride is left exposed to sunlight ? State the type of chemical reaction in this change.
Answer: White colour changes to grey. Decomposition reaction
2. Which bases are called alkalis ? Give an example of alkalis.
Answer: Water soluble bases are called alkalis . NaOH / KOH / Ca (OH)2 / Mg (OH)2 (Any one)
3. Write the names and chemical formula of the products formed by the action of chlorine on slaked lime.
Answer: Calcium Oxychloride / Bleaching Powder .CaOCl2
4. State in brief the reaction involved in harnessing nuclear energy from uranium. Mention any two environmental hazards involved in harnessing nuclear energy.
Answer: Reaction involved is : Nuclear fission ½
Nucleus of uranium, when bombarded with low energy neutrons, splits into lighter nuclei releasing tremendous amount of energy.
Environmental hazards – (Any two of the following)
(i) Improper nuclear waste storage and disposal results in environmental contamination.
(ii) Risk of accidental leakage of nuclear radiations affects the environment.
(iii) Genetic mutation / Skin cancer
5. What happens when an iron strip is put into separate beakers containing aqueous solutions of copper sulphate and zinc sulphate ? Where is iron placed in the activity series with respect to copper and zinc ? Describe the steps involved in the extraction of zinc from its sulphide and carbonate ores. Support your answer with balanced chemical equation for the chemical reactions involved in the process.
Answer: Colour of copper sulphate solution changes from blue to light green.
Reddish brown substance is deposited on the iron nail.
No change is observed in zinc sulphate solution.
Iron is above copper and below zinc. / Iron is between copper and zinc in the reactivity series of elements. 1
Roasting : 2 ZnS + 3 O2  ---Heat------à2 ZnO + 2 SO2
Calcination : ZnCO3 ---Heat------àZnO + CO2
Reduction : ZnO + C  ------à Zn + CO
6. (a) Give an example of a metal which  (i) is a liquid at room temperature. (ii) is kept immersed in kerosene for storing. (iii) is both malleable and ductile. (iv) is the best conductor of heat.
(b) Name the process of obtaining a pure metal from an impure metal through electrolysis. Suppose you have to refine copper using this process, then explain with the help of a labelled diagram the process of purification, mentioning in brief the materials used as (i) anode, (ii) cathode and (iii) electrolyte.
Answer: a) (i) Mercury / Hg  (ii) Na / K   (iii) Cu / Zn / Al / Au / Ag (or any other)
(iv) Ag / Cu  
b) Electrolytic refining:
Description : Draw diagram
On passing current through the electrolyte, the pure metal from anode dissolves and an equivalent amount of pure metal from electrolyte is deposited on the cathode. Insoluble impurities settle down at the bottom. (Note : The description should mention the following: )
Cathode : Pure copper            Anode : Impure copper
Electrolyte : Acidified copper sulphate solution

7. Describe an activity to (i) demonstrate the pattern of magnetic field lines around a straight conductor carrying current, and (ii) find the direction of the field produced for a given direction of current in the conductor. Name and state the rule to find the direction of magnetic field associated with a current carrying conductor. Apply this rule to determine the direction of the magnetic field inside and outside a current carrying circular loop lying horizontally in the plane of a table. Assume that the current through the loop is clockwise.
Answer: draw diagram
(i) A thick copper wire is passed through a cardboard and the ends of the wire are attached to the battery and key. When current is passed through the wire as shown, the iron filings on tapping the cardboard align themselves in the form of concentric circles whose centre lies on the wire. On placing a compass needle at a point (say P) the direction of the north pole of the needle gives the direction of field at the point P.
(ii) When the direction of current is downwards the direction of magnetic field lines is clockwise.
Rule : Right hand thumb rule
Statement : Imagine that you are holding a current-carrying straight conductor in your right hand, such that the thumb points towards the direction of the current, then your fingers will wrap around the conductor in the direction of magnetic field lines.
8. What is electromagnetic induction ? State different ways of inducing current in a coil. Suggest the most convenient situation for inducing current in a coil. State the situation in which the induced current in the coil is found to be the highest. Name and state the rule used to know the direction of the induced current.
Answer: Electromagnetic induction is the process by which :- a changing magnetic field in a conductor induces a current in another conductor / motion of a magnet with respect to the coil produces an induced potential difference which sets up an induced electric current in the circuit.
Different ways of inducing current :
(i) by moving a coil in a magnetic field
(ii) by changing the magnetic field around a coil
Most convenient situation :
To move the coil in the magnetic field.
Condition for maximum induced current : When the direction of motion of the coil is at right angles to the magnetic field.
Fleming's right hand rule : Stretch the thumb, forefinger and middle finger of right hand so that they are perpendicular to each other such that the forefinger points in the direction of the magnetic field, the thumb shows the direction of motion of conductor, then the middle finger will show the direction of induced current.
9. What is an ore ? Name the steps involved for obtaining zinc metal from its sulphide ore. Write the chemical equations for the reactions involved.
Ans: Ore : A mineral from which a metal can by extracted profitably
Steps for obtaining zinc from its sulphide ore :
(i) Roasting
Zn S + O2 -------heating ------à ZnO + SO2
(ii) Reduction
Zn O + C – heating----à Zn + CO ½
10. (a) State Fleming’s left hand rule. (b) For what purpose is it used ? (c) Name two devices where this rule is applicable.
Ans : (a) Fleming's Left Hand Rule : Stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular to each other. If the forefinger points in the direction of magnetic field and middle finger points in the direction of current, then the thumb will point in the direction of motion/force on the conducter.
(b) For finding the direction of force exerted on a current carrying conductor placed in a magnetic field
(c) Devices: Electric motor / Electric fan / Electric grinder / Electric meters such as Galvanometer. ammter etc. (Any Two)

CLASS X SAMPLE PAERS 2013-2014(Sep) 
Mathematics SA 1 (with Solution) 
9th science sample paper- S A -1- 2013-1          
9th science sample paper-SA1-2013-1-Solution   
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9th science sample paper- S A -1- 2013-2
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9th science sample paper-SA1-2013-2-Solution
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