expert tips in physics and chemistry

8/12/2019 Expert Tips in Physics and Chemistry

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Expert Tips - Physics (Class 12)

Dear students,

How is your preparation for this years physics exam? Is it very good, good, so-so or you have

no idea where you stand? Wherever you stand and whatever be your strategy, we atmeritnation.com are always here to help you score well.

You dont have to be a Physicist to score marks in Physics. A good strategy can however helpyou score cool marks even you have hated this subject the most. Here is a small analysis just to

help you understand the fact that it is easy to score in physics.

Based on the question pattern of 2011 and 2012, the number and marks assigned to differenttypes of questions are as follows:

Question Type Marks (%) Number of

Question (%)

Definition Based 36 29

Formula Based 6 10

Derivation 13 13

Law/Principle (application) 6 8

Numerical 26 27

Memory 13 13

The total marks allotted to this paper is 70.

Study all the definitions and derivations and memorize all the formulae and you are guaranteed

with approximately 38 marks.

If you are good with the concepts, then the numerical and application of laws/ principles can giveyou approximately 22 marks.
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If you have covered all the topics in the syllabus and memorized all the terms and points, thenapproximately another 10 marks is on your side.

Unit-wise distribution of marks:

Units Marks1. Electrostatics 8

2. Current Electricity 7

3. Magnetic Effect of Current and Magnetism 8

4. Electromagnetic Induction and Alternating Current 8

5. EM waves 3

6. Optics 14

7. Dual Nature of Radiation and Matter 4

8. Atoms and Nuclei 6

9. Electronic Devices 7

10. Communication Systems 5

CHEMISTRY IMPORTANT QUESTIONS

All equations must be balanced. A reaction, which is not balanced, is not an equation.Ques:Complete the following chemical reaction equations: (i)P4+ SO2Cl2(ii)XeF4+

H2O (CBSE 2010 Set 3, Q 30)

Model Ans:

(i) P4+ 10 SO2Cl2 4 PCl5+ 10 SO2

(ii) 6 XeF4+ 12 H2O 4 Xe + 2 XeO3+ 24 HF + 3 O2

Reasoning questions carry one mark each and demand to-the point and precise answer.Ques:NF3is an exothermic compound but NCl3is endothermic compound. (CBSE 2010 Set 3,

Q 30)

Model Ans: The instability of NCl3is due to the weak NCl bond. This is due to the largedifference in the size of nitrogen and chlorine atoms. On the other hand, atoms of both nitrogen

(75 pm) and fluorine (72 pm) are small sized. Thus, bonding in NF3is quite strong and it is anexothermic compound.

Ques: Account for the following: (CBSE 2009 Set 1, Q 23)(i) NH3is a stronger base than PH3.

(ii) Sulphur has a greater tendency for catenation than oxygen.(iii) Bond dissociation energy of F2 is less than that of Cl2.

Model Ans: (i) On moving from nitrogen to phosphorus, i.e., down the group, the atomic size

increases. As the size of the central atom increases, the lone pair of electrons occupy a larger


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volume. Consequently, the electron density, and hence, the basic strength decrease. Thus, NH3is astronger base than PH3.

(ii) The tendency for catenation depends upon the bond energy. The bond energy of a sulphur

molecule is more than that of an oxygen molecule. Thus, the sulphur sulphur bond strength is

higher, and as a result, the tendency of catenation is also higher. Sulphur shows catenation up toeight atoms.

(iii) Bond dissociation energy of fluorine is less than that of chlorine. It is due to the low value of

electron affinity of small-sized fluorine. Also, the value of enthalpy of hydration of fluorine ismuch higher than that of chlorine.

Attempting numericals:Start the answer by writing the skeleton formula in standardnotation followed by substitution of values with units. Numericals carry step-wisemarking. At times it happens that due to lack of time these questions remain unattempted.

In that case, even if you write the general formula and substitute the values, you manage

to score half of the total marks alloted to the question.

Ques: A solution prepared by dissolving 1.25 g of oil of winter green (methyl salicylate) in 99.0 g

of benzene has a boiling point of 80.31 C. Determine the molar mass of this compound. (B.P. ofpure benzene = 80.10 C and Kb for benzene = 2.53 C kg mol1) (CBSE 2010 Set 3, Q 21)

Conversion of units should be taken care of. The final answer must be written with units. Always support your answers with structures, examples, equations and graphs even if the

question does not ask for it. Memory-based questions are usually asked from the chapters like polymers, chemistry in

everyday life, biomolecules and surface chemistry.


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Example :

Ques:Define the term, homopolymerisation giving an example.

(2012 CBSE Set 1, Q8 Polymer)

Ques:What is meant by coagulation of a colloidal solution? Describe briefly any three methods bywhich coagulation of lyophobic sols can be carried out.

(2012 CBSE Set 1, Q11 Surface Chemistry)

Ques:What is meant by (i) Peptide linkage (ii) biocatalysts?

(2012 CBSE Set 2, Q14 Biomolecules)

Ques:Explain the following terms giving one example of each type:

(i) Antacids,

(ii) Disinfectants,

(iii) Enzymes.

(2012 CBSE Set 3, Q27 Chemistry in Everyday Life)

expert tips in physics and chemistry

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