Cbse Board Exam Papers

C.B.S.E. EXAM PAPER – 2004 BIOLOGY (THEORY) – XII DELHI SET – I TIME : 3 HOURS

M. MARKS : 70

GENERAL INSTRUCTIONS: (i) This question paper consists of four Sections A, B, C and D. Section A contains 5 questions of one mark each, Section B is of 10 questions of two marks each, Section C is of 10 questions of three marks each and Section D is of 3 questions of five marks each. (ii) All questions are compulsory. (iii) There is no overall choice. However, an internal choice has been provided in some questions. You have to attempt only one of the choices in such questions. (iv) Question numbers 1 to 5 are to be answered in one word or one sentence each. (v) Question numbers 6 to 15 are to be answered in approximately 20-30 words each. (vi) Question numbers 16 to 25 are to be answered in approximately 30-50 words each. (vii) Question numbers 26 to 28 are be answered in approximately 80-120 words each..

SECTION – A Q.1. Name the condition in humans in which the blood cholesterol content becomes abnormally high. (1) Q.2. Define vernalisation. (1) Q.3. Many villagers near industrial area suffer from “blue baby syndrome”. How is this problem caused ? (1) Q.4. A cardiologist observed an elevated ST segment in the ECG of a patient. What is it indicative of ? (1)

Q.5 Why is quarrantine a must before introduction of a plant species from a different country ? (1)

SECTION – B Q.6. What is meant by apoplast pathway ? Why does it occur in cortex and not in endodermis ? (2) Q.7. Where is pneumotoxic center located in humans ? What is its significance in breathing ? (2) Q.8. How is a disease-resistant plant selected for successful breeding ? (2) Q.9. Why is the process of fertilization in a flowering plant referred to as double fertilization ? Explain. (2) Q.10 Name the watery fluid secreted from Brunner’s gland in the duodenum. Mention its any two characteristics. What role does it play inside the duodenum ? (2) Q.11 How is opening and closing of stomata controlled ? Explain. (2) Q.12 Why is the length of a food chain in an ecosystem generally limited to 3-4 trophic levels ? Explain with an example. (2) Q.13 In what form do the terrestrial reptiles excrete their nitrogenous waste ? How is this kind of excretion to the land vertebrates which lay shelled eggs ? (2) Q.14 Explain briefly how computed tomography (CT) helps the doctors in pinpointing the defects in the patient’s body. (2) Q.15 What is eutrophication ? Explain with reference to aquatic ecosystem. (2)

Or Name any two source organisms of agar. List any four areas in which agar has wide application. (2)

SECTION – C Q.16 Name the two groups of nephrons on the basis of their position in the kidney. How are they different from each other ? (3) Q.17 How is the halophyte Rhizophora adapted to survive in its habitat ? Explain. (3) Q.18 When and why does photo-respiration take place in plants ? How does this process result in a loss to the plant ? (3) Q.19 Explain the sliding filament theory of muscle contraction. (3) Q.20 What is special of “FlavrSavr” variety of tomato ? Why is it preferred to its normal native variety? (3) Q.21 Draw a labeled sketch of L.S. of a human grinding tooth fixed in the socket. (3)

Or Draw a schematic diagram to show the spinal reflex arc. Label the components of the pathway. (3) Q.22 Name the organism involved in symbiotic nitrogen fixation. What are the components needed for this purpose ? Explain their role. (3) Q.23 Differentiate between inbreeding and heterosis. The outcome of which one is superior in performance and why? (3)

Q.24 What is the optimum percentage of forest area recommended by the National Forest Policy (1988) for the plains and the hills respectively ? List any four problems caused due to deforestation. (3) Q.25 Why is the human placenta referred to as haemochorial type ? Name the hormone it secretes to facilitate parturition. (3)

SECTION – D Q.26 Where does Calvin cycle take place in chloroplast ? Explain the cycle. (5)

Or Where is electron transport system operative in mitochondria ? Explain the system highlighting the role of oxygen. (5) Q.27 Describe the hormonal control of the reproductive system in human male. (5) Q.28 Define totipotency. Explain the two different routes of regenerating plantlets from callus culture. (5)

Sample Paper - I PHYSICS

Time: 3 Hrs CLASS – XII M.Marks: 70 GENERAL INSTRUCTION:

1. 2. 3. 4. 5. 6.

Questions 1-5 carry 1 mark each. Questions 6-12 carry 2 marks each. Questions 13-24 carry 3 marks each. Questions 25-27 carry 5 marks each. Use Log Tables, if necessary. Please write down the serial number of the question before attempting it.

Q1. Give a reason to show that microwaves are better carriers of signals for long range transmission than radio waves. Q2. How does the energy gap in an intrinsic semiconductor vary, when doped with a pentavalent impurity? Q3. State the condition in which terminal voltage across a secondary cell is equal to its e.m.f. Q4. Draw an equipotential surface in a uniform electric field. Q5. If the number of turns of a solenoid is doubled, keeping the other factors constant, how does the self-inductance of the solenoid change? Q6. Briefly explain how the distance of an inferior planet from earth can be determined? Q7. Using Gauss' law, show that no electric field intensity exists inside a hollow charged conductor. Q8. Draw the logic symbol of a 2 - input NOR gate. Write down its truth table. Q9. Briefly explain how the distance of a superior planet can be determined from earth. Q10. Draw the logic symbol of a 2-input NAND gate. Write down its truth table. Q11. Four capacitors are connected as shown in the figure given below :

Calculate the equivalent capacitance between the points X and Y. Q12. Draw the graph showing the variation of binding energy per nucleon with the mass number of different nuclei. State two inferences from this graph. Q13. In a single slit diffraction experiment, if the width of the slit is doubled, how does the (i) intensity of light and (ii) width of the central maximum change. Give reason for your answer. Q14. If the wavelength of incident light on a (i) concave mirror, and (ii) convex lens is increased, how will the focal length of each of these change ? Q15. A ray of light passes through an equilateral glass prism, such that the angle of incidence is equal to the angle of emergence. If the angle of emergence is 3/4 times the angle of the prism, calculate the refractive index of the glass prism. Q16. A rectangular coil N turns and area of cross-section A, is held in a time-varying magnetic field given by B = B0 sin t, with the plane of the coil normal to the magnetic field. Deduce an expression for the e.m.f. induced in the coil. Q17. Draw the graph showing variation of thermo e.m.f. of a thermo-couple with the temperature difference of its junction. How does its neutral temperature vary with the temperature of the cold junction? Q18. Derive an expression for the electric potential at a point along the axial line of an electric dipole. Q19. A copper voltameter is in series with a heater coil resistance 0.1 ohm. A steady current flows in the circuit for 20 minutes, and a mass of 0.99 gm of copper is deposited at the cathode. If the electro-chemical equivalent of copper is 0.00033 gm/coulomb, calculate the heat generated in the coil. Q20. State Huygen's postulates of wave theory. Sketch the wavefront emerging from a (i) point source of light and (ii) linear source of light like a slit. Q21. State the conditions for total internal reflection of light to take place at an interface separating two transparent media. Hence derive the expression for the critical angle in terms of the speeds of light in the two media.

Q22. State the dependence of work function on the kinetic energy of electrons emitted in a photocell. If the intensity of incident radiation is doubled, what changes occur in the stopping potential and the photoelectric current. Q23. With the help of a labelled circuit diagram, explain how will you determine the internal resistance of a primary cell using a potentiometer. State the formula used. Q24. A short bar magnet of magnetic moment 0.9 joule/tesla, is placed with its axis at 45o to a uniform magnetic field. If it experiences a torque of 0.063 joule, (i) calculate the magnitude of the magnetic field and (ii) what orientation of the bar magnet corresponds to the stable equilibrium in the magnetic field? Q25. State the postulates of Bohr's model of hydrogen atom. The electron, in a given Bohr orbit has a total energy of -1.5 eV. Calculate its (i) kinetic energy. (ii) potential energy and (iii) wavelength of light emitted, when the electron makes a transition to the ground state. (Ground state energy = -13.6 eV) Q26. For a given a.c. circuit, distinguish between resistance, reactance and impedance. An a.c. source of frequency 50 hertz is connected to a 50 mH inductor and a bulb. The bulb glows with some brightness. Calculate the capacitance of the capacitor to be connected in series with the circuit, so that the bulb glows with maximum brightness. Q27. Drawing a labelled circuit diagram, explain the working principle of a commonemitter transistor amplifier. State the phase relation between input and output signals.

Or With the help of a labelled circuit diagram, explain how a transistor oscillator works. Useful constants (i) Planck's constant, h = 6.6 x 10-34 Js (ii) Speed of light in air, c= 3 x 108 m s-1

Question 1

10.0g of CaCo3 on heating gave 4.4g of Co2 and 5.6g of CaO. Show that these observations are in agreement with law of Conscruation of mass?

Question 2

Define Molarity? Question 3

How is presure of a given samples of gas related to temperature at constant volume? Question 4

Calculate the number of electrons, Porotons and Neutrons is Phosphorus atom. (Mass number-31, atomic number-15) ? Question 5 What are isotopes ? Question 6

Write the electronic configuration of Hydrogen? Question 7

What is the total number of groups in thelong form of periodic table? Question 8

What is Hybridisation? Question 9

Give the Structure of anion which is instructural with BF 3? Question 10

What name is given to Carbon reduction process for extracting the metal ? Question 11

Define Hydrogen bond? Question 12

Differentate between a metallic bond and covalent bond? Question 13

Write electron dot structures of H2S and CH4? Question 14

What are isoelectronic ions? Question 15

What is the trend of metallic character on going down from top to bottom in a group? Question 16

What is modern periodic law ? What is periodicity? Question 17

Calculate the energy of a photon of light having frequency of 1.0X 10 15 S-1 Plankis constant h = 6.63x10 -34 J-S? Question 18

What is Dalton's law of partial pressures?

Question 19

A gas having molecular mass 84.5g.mol-1 enclosed in a flask at 27oC has a pressure of 1.5 atmosphere. Calculate the density of the gas under these conditions? Question 20

What do you mean by S.T.P and N.T.P. Write it the value? Question 21

Define Avogadros law? Question 22

A given solution of NaoH contains 2.00g of NaoH per litre of solution. Calculate the molarity of this solution? Question 23

Calculate the mass of one atom of Calcium? Question 24

How many significant figures are there in each of the following numbers (1) 6.023x10 23 (2) 0.0256 (3) 4.0026 (4) 0.050. Question 25

Name two ores of Iron and two of copper? Question 26

What do you mean by weathering? Question 27

What is the simplest formula of the Compound which has the following percentage composition : Carbon 80%, Hydrogen 20%. If the molecular mass is 30, calculate its molecular formula? Question 28

Distinguish between Crystalline and amorphous solids? Question 29

What is heat of vaporisation in a liquid? Question 30

What do you mean by presure of a gas? How would you measure the atmospheric pressure? Question 31

What information does a chemical equation convey?

Question 32

Classify the following substances into elements, compounds and mixtures. Incase of mixture, indicate whether it is homogeneous or heterogeneous. Question 33

State Modifications in modern Atomic theory over Dalton's Atomic theory. Question 34

Define Dipole moment. What are its applications? Answers: Question 1

10.0g of CaCo3 on heating gave 4.4g of Co2 and 5.6g of CaO. Show that these observations are in agreement with law of Conscruation of mass? Ans Mass of the reactants = 10.0g. Mass of the Products = 4.4+5.6 = 10.0g. Since mass of the reactants is equal to the mass of the products therefore, these observations are in agreement with law of conservation of mass. Question 2

Define Molarity? Ans. The Molarity of a solution is defined as the number of moles of solute per litre of solution. The Wait of molarity is moles per litre (mol L-1) Question 3

How is presure of a given sample of gas related to temperature at constant volume? Ans. PαT Question 4

Calculate the number of electrons, Porotons and Neutrons in Phosphorus atom. (Mass number-31, atomic number-15) ? Ans. Number of electrons = Atomic number =15 Number of protons = Atomic number =15 Number of neutrons = Mass number - Atomic number 31 - 15 = 16

Question 5 What are isotopes ?

Ans. Atoms of some element having different mass numbers. eg. Hydrogen has three isotopes potium (H), deutorium (D) and tritium (T), having mass numbers 2, 2 and 3 respectively. Question 6

Write the electronic configuration of Hydrogen? Ans. Hydrogen (Act No - 1) 1H : 1S 1 OR 1S Question 7

What is the total number of groups in thelong form of periodic table? Ans. 18 Question 8

What is Hybridisation? Ans. The Phenomenon of intermiscing of atomic orbitals of slightly different energy of the atom (by redistributing their energies) to form new set of orbitals of equiralent energies and identical shape. Question 9

Give the Structure of anino which is instructural with BF 3? Ans. NO3 Question 10

What name is given to Carbon reduction process for extracting the metal ? Ans. Smelting. Question 11

Define Hydrogen bond? Ans. Hydrogen bond is defined as the electrostatic force of attraction which exists between the covalently bonded hydrogen of one molecule and the electroneative atom of the other molecule. This represented by dotted line (--------------). For example in case of hydrogen fluoride the hydrogen bond exists between H atom of one molecule and flourine atom of another molecule. H-------F---------H----------F----------H------------F----------------.

Question 12

Differentate between a metallic bond Ans. 1. The Simultaneous force of attraction between the mobile electrons and the positive Kernels constitutes a metallic bond. 2. It is a weak bond because mobile electons are simultaneously attracted by a large number of kernels. 3. This bond is non - directional

and covalent bond? 1. The mutual sharing of electrons between the combining atom of the same or different element is called a covalent bond. 2. It is a strong bond because the bonded electron pair is strongly attracted by two nuclei. 3. This bond is directional.

Question 13

Write electron lot structures of H2S and CH4? Ans. H2S -- Hydrogen Sulphide molecule .. H+H+.S. --- H:S:H or H-S-H .. CH4 -- Methane molecule . H H 4H. + .C.- H:C:H or H:C:H . H H Question 14

What are isoelectronic ions? Ans. The ions having same number of electrons but different nuclear charge. e.g:N3-, O2-, F-, Na+, Mg2+, Al 3 + P3-, S2-, u-, K+, Ca2+, SC 3+ Question 15

What is the trend of metallic character on going down from top to bottom in a group? Ans. Metallic character increases on going down a group because ionisation energy decreases on moving down a group. Question 16

What is modern periodic law ? What is periodicity? Modern periodic law -- The modern periodic law states that the physical and chemical properties of the elements are the periodic Function of their atomic numbers. Periodicity -- The periodical repetition of elements with similar properties after certain regular intervals when the elements are arranged in order of increasing atomic number is called periodicity.

Question 17

Calculate the energy of a photon of light having frequency of 1.0X 10 15 S-1 Panckis constant h = 6.63x10 -34 J-S? Ans. The energy of photon is given by E=RV Frequency V is given to be = 1.0x10 15 S-1 and Plank's Constant h = 6.63x10-34 J-S E= 6.63x10-34 J-SX1.0X10 15 S-1 = 6.63 x 10-19 J. Question 18

What is Dalton's law of partial pressures? Ans. The Dalton's law of partial pressures states that `At Constant temperature, the pressure discerted by a mixture of two or more non reacting gases enclosed in a definite volume, is equal to the sum of the individual pressures which each gas would exert if present alone in the same volume. The individual pressure of gases are known as partial pressures. If P is the total pressure of the mixture of non reacting gases at temperature T and Volume V, and P1, P2, P3 --- represent the partial pressures of the gases, than P= P1+P2+P3 + -------------------------(T, Vare constant). Question 19

A gas having molecular mass 84.5g.mol-1 enclosed in a flask at 27oC has a pressure of 1.5 atmosphere. Calculate the density of the gas under these conditions? Ans. P=1.5 atm T=300K M=84.5 g.mol-1 R=0.0821 L atm K-1 mol-1 The relationship between pressure and density is P= DRT M D= PM=1.5x84.5 = 5.416 gl-1 RT= 0.0821x300 Density of gas is 5.416 gl-1

Question 20

What do you mean by S.T.P and N.T.P. Write the value? Ans. S.T.P. means standard temperature and pressure or N.T.P. meaning normal temperature and pressure . In brief S.T.P. or N.T.P. refer to Temperature =0oC or 273; 15K Pressure = 1 atm, or 760 mm of Hg or 760 tors or 101.325 kpa. Question 21

Define Avogadros law? Ans. Avogadro is law states that equal volume of all the gases under similar conditions of temperature and pressure contain equal number of molecules. For example 22.4 litres of all the gases at 273K and 1 atm. Pressure contain 6.02x10 23 molecules. It follows, therefore that volume of the gas is directly proportional to the number of molecules. V α N (Temperature and Pressure constant) The number of molecules (CN) of any gas is directly proportional to its number of moles (n) Thus, V α N (Temperature and Pressure constant). Question 22

A given solution of NaoH contains 2.00g of NaoH per litre of solution. Calculate the molarity of this solution? Ans. Molar mass of NaoH = 40.00g 2g.NaoH = 2.00 mole NaoH = 0.05 mole NaoH 40.00 Molasity = Mole of solute Volume of solution an litres =0.05= 0.05M 1 Molarity of solution will be 0.05M. Question 23

Calculate the mass of one atom of Calcium? Ans. Mass of 6.023x10 23 atoms of Calcium =Gram Molecular mass of Calcium = 40g. Mass of 1 atom of Calcium = 40 g 6.023x10 23 - 23 = 6.6x10 g. Mass of one atom of Calcium is 6.6x10-23 g.

Question 24

How many significant figures are there in each of the following numbers (1) 6.023x10 23 (2) 0.0256 (3) 4.0026 (4) 0.050. Ans. (1) 6.023x10 23 has three significant figures. The exscponential term does not add to the number of significant figures. (2) 0.0256 has three significant figures, zeros to the lbt of the first non. Zeros digit in a number are not significant. (3) 4.0026 has five significant digits, zeros in between the non zero digits are significant. (4) 0.050 has two significant digits, zeros following a non zero digit to the right of the decimal point are significant. Question 25

Name two ores of Iron and two of copper? Ans. Haematite (Fe2 O3) Magnetite (Feo Fe2O3) Ores of Iron Malachite (cuco3.CuoH2 Copper Pyrites (CuFeS2) Ores of Copper. Question 26

What do you mean by weathering? Ans. The process of selective esctraction of igneous rocks by rain water, containing Carbon dioxide and other acids resulting in the dissolution of solute ions lke Na+, Ca2+, Fe2+, Mg2+etc and leaving behind unsolute residue as rocky material (TiO2, Fe2O3, SiO2 etc.)

Question 27

What is the simplest formula of the Compound which has the following percentage composition : Carbon 80%, Hydrogen 20%. If the molecular mass is 30, calculate its molecular formula? Ans. Calculate of imperical formula Element Percentage At.mass Relative no Simple ratio Simplest short of moles of moles no ratio C 80 12 80/12=6.66 6.66=1 1 6.66 H 20 1 20/1=20 20 =3 3 6.66 Empirical formula is CH3 Calculate of molecular formula Empirical formula mass = 12x1 + 1x3 = 15 H= Molecular mass Empirical formula mass =30 15 = 2 Molecular formula = Empirical formula x2 = CH3 x2 = C2H6

Question 28

Distinguish between Crystalline and amorphous solids? Ans. Crystalline Solids Amorphous Solids 1. The internal arrangement of particles is 1. The internal arrangement of particles is regular. irregular. 2. There is regularity in the external form when 2. There is no regularity in the external form crystals are formed when amorphours solids are formed. 3. They have a sharp melting points 3. They do not have sharp melting ponts. 4. They do not have characteristic heat of 4. They have characteristic heats of jusion. fusion. 5. Crystalline solids give a regular cut with a sharp5. Amorphous solids give irregular cut. edged knife. 6. Crystalline solids are regarded as true solids.

6. Amosphous solids are regarded as super cold liquids or pseudo solids.

7. Amorphous solids are isotropic in nature. 7. Crystalline solids are anisotropic. This implies that This implies that various physical properties physical properties such as rexrective index, are same in all the directions. This is because conductivity, thermal expansion etc are different in of the random arrangements of particles. different directions. This is due to orderly arrangement of particular.

Question 29

What is heat of vaporisation in a liquid? Ans. Heat of Vaporisation :- The amount of heat required to convert a liquid into gas at a constant temperature is known as the heat of vaporisation. Molar heat of vaporisation (__∆_ Hvap) is defined as the amount of heat required to convert one mole of a liquid to gas at a constant temperature. A liquid having stronger attractive forces has higher value of heat of vaporisation. Water has relatively high heat of vaporisation because of strong hydrogen bonds among its molecules. When one mole of water evaporates at 298k it absorbs 44.180 KJ of energy. H2O(e) ------------ H2O(g) ; ∆Hvap = + 44.180 KJ The molar heat of vaporisation of water at 298 K is thus, 44.180 KJ. Frederick Trouton, in 1884, discovered that for many liquid molar heat of vaporisation in calories per mole divided by the normal boiling point in degree kelvin is a constant : 21 Cal/Kmol. ∆Hvap = 21 Cal K-1 mol -1 Tb The above mentioned rule is known as Trouton's rule. This rule is only approximate. Heat of vaporisation for Benzeneis 30.8 KJ/mol at its boiling point.

Question 30

What do you mean by presure of a gas? How would you measure the atmospheric pressure? Ans. Pressure of a gas :- A gas enclosed in a vessel exerts on outward force its walls.The outward force per unit area of the walls is termed as gas pressure. The SL unit of pressure is neuton per square metre (Nm-2) which is also called pascal (Pa). Atmospheric pressure and its measurement - The earth is surrounded by a thick blanket of air called atmosphere. The pressure exerted by the gases of the atmosphere on the surface of the earth is called atmospheric pressure. The atmosheric pressure can be measured by a simple device called barometer. A simple borometer can be made by filling mercury in a tube (Longer than 76 cm.) closed at one end and inverting it in an open vessel containing mercury. The mercury level in the tube adjusts itself and stands approximately 76 cm above the level of mercury in the open vessel. The height of mercury column in the tube gives a measure of atmospheric pressure. The height of the column decreases when the pressure of the atmosphere decreases whereas the height of the column increases with the increase in the atmospheric pressure. Draw a diagram

Question 31

What information does a chemical equation convey? Ans. A Chemical equation conveys bath qualitative as well quantitative information.. 1.Qualitative:- A Chemical equation tells us the names of the various reactants and products. 2.Quantitative:- It expresses. (a) The relative number of molecules of the reactants and products taking part in the reaction. (b) The relative number of moles of reactants and products. Thomson, Neils Bohr, Chadurick and others who revealed the inner structure of atom. In the light of their findings Dalton's Atomic theory was suitably modified. The main modifications made in thie theory are as follows(I) Atom is no longer considered to be indivisible- It has been found that an atom has a complete structure and is composed of sub atomic particles such as a electrons., protons and neutrons. (ii) Atom of the same element may not be similar in all respects Atoms of same element may possess different relative masses. For example we have two different types of atoms of chlorine with relative masses 35 a.m.u and 37 a.m.u respectively. Such atoms of the same element which possess different masses are called isotopes. (iii) Atoms of different elements may be similar in one or more respects - There are certain atoms of different elements which possess same relative masses. For example, relative mass of calciun and argon is same (40 a.m.u). Such atoms of different elements which possess same mass are called isobars. (iv) Atom is the smallest unit which takes part an chemical reactions: Though atom is composed of sub-atomic particles, yet it is the smallest particle which takes part in chemical reactions. (v) The rate in which atoms unite may be fixed and integral but may not be simple -- For Example in sugar molecule (C12 H22 011) the rate of C, H and O atoms is 12:22:11 which is not simple. (vi) Atoms of one element can be changed into atoms of (a) The relative masses of reactants and products.

Question 32

Classify the following substances into elements compounds and mixtures. Incase of mixture, indicate whether it is homogeneous or heterogeneous. Ans. (I) Mixture (Heterogeneous) (ii) Mixture (Homogeneous) (iii) Mixture c (Heterogeneous) (iv) Mixture (Homogeneous) (v) Element (vi) Mixture (Homogeneous) (vii) Element (viii) Compound (ix) Compound. Question 33

State Modifications in modern Atomic theory over Dalton's Atomic theory. Ans. Modern Atomic Theory :- Towards the end of 19th century and in the beginning of 20th Century new discoveries were made by Sir T.T. other element -- For example, atoms of nitrogen can be changed into oxcygen atoms by interaction with xrays. This is called transmutation. The mass of atom can be changed into energy -- According to Einstein's equation E=mc2 CE = Energy, m = mass, C= the velocity of light i.e. 3x10 10 cm sec_1, mass and energy are inter convertible. Thus, atom is no longer indestructible. Hwever, during chemical reactions, atom remains unchanged.

Question 34

Define Dipole moment. What are its applications? Ans. Dipole moment - Dipole moment is defined as the product of the magnitude of charge on any one of the atoms and the distance between them. Dipole moment is represented by a Greek Letter 'M'. It cen be escpressed methomatically as -M = exd Where e = Charge on any one of the atoms d = Distance between the atoms. Since the charge 'e' is of the order of 10 -10 e.s.u and 'd' is of the order of 10-8 cm, then M, which is the product of 'd' and 'e' is of the order of 10-18, e.s.u cm. This unit is Debye and is represented by D.Thus, 1D = 1x10-18 e.s.u. cm For example dipole moment of HC is 1.03x10-18 e.s.u c.m. and is expressed as 1.03 D. Applications of dipole moment - Some of the applications are as follows(I) Distanction between polar and non-polar molecules-- The molecules having dipole moment are called polar molecules whereas molecules having zero dipole momemt are said to be non-polar molecules. For example -(a) Molecules such as H2, Nz, Oz Clz etc. have been polar bonds and zero value of dipole moment. (b) Molecules such as Co2, Bf3, CH4 etc have polar bonds but zero value of dipole moment. (c) Molecules such as HF, HCE, NH3, H2O, Nf3 have polar bonds and their dipole moment is greater then zero. They are polar molecules. (ii) Tonic Character in a molecule -- Dipole moment gives an idea about the ionic character in a bond or a molecule, For example calculating the percentage of ionic character in Hcl molecule. Experiments have shown that the dipole moment of Hcl is 1.03 D and its bond length is 1.257 A: Now for 100% ionic character to charge development on H and cl atoms would be 4.8x10-10 e.s.u. Therefore, dipole moment in case of 100% ionic character is given as : M ionic = 4.8x10-10 x 1.275x10-8 e.s.u cm