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(i) Atomic number: The atomic number is the total number of protons present in the atom. For example, the atomic number of sodium is 11. It contains 11 protons and 11 electrons. (ii) Mass number: It is the sum of the number of neutrons and the number of protons. For example, the atomic number of magnesium is 12 which is equal to the number of protons, the number of neutrons of magnesium is 12. The mass number is equal to 24 (12+12). (iii) Isotopes are the elements having same atomic number but different mass number. They have same chemical properties as the number of valence electrons are same. For example, 6C12, 6C13, 6C14 are the three isotopes of carbon. They have same atomic number but different mass number due to difference in the number of neutrons. (iv) Isobars: They are elements having the same mass number but different atomic number. For example. 18Ar40, 19K40 are isobars having the same atomic mass but different atomic number. The two uses of isotopes are: Nuclear weapons and nuclear power require large quantities of isotopes of uranium.An isotope of cobalt is used in the treatment of cancer. Video Explanation 
[10/12, 6:52 PM] Anshuman: Q1. Look at the activities listed below. Reason out whether or not work is done in the light of your understanding of the term ‘work’. (a) Suma is swimming in a pond. (b) A donkey is carrying a load on its back. (c) A wind mill is lifting water from a well. (d) A green plant is carrying out photosynthesis. (e) An engine is pulling a train. (f) Food grains are getting dried in the sun. (g) A sailboat is moving due to wind energy. Work is done whenever the given conditions are satisfied: (i) A force acts on a body. (ii) There is a displacement of the body. (a) While swimming, Suma applies a force to push the water backwards. Therefore, Suma swims in the forward direction caused by the forward reaction of water. Here, the force causes a displacement. Hence, work is done by Seema while swimming. (b) While carrying a load, the donkey has to apply a force in the upward direction. But, displacement of the load is in the forward direction. Since, displacement is perpendicular to force, the work done is zero. (c) A wind mill works against the gravitational force to lift water. Hence, work is done by the wind mill in lifting water from the well. (d) In this case, there is no displacement of the leaves of the plant. Therefore, the work done is zero. (e) An engine applies force to pull the train. This allows the train to move in the direction of force. Therefore, there is a displacement in the train in the same direction. Hence, work is done by the engine on the train. (f) Food grains do not move in the presence of solar energy. Hence, the work done is zero during the process of food grains getting dried in the Sun. (g) Wind energy applies a force on the sailboat to push it in the forward direction. Therefore, there is a displacement in the boat in the direction of force. Hence, work is done by wind on the boat. Q2. An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. The initial and the final points of the path of the object lie on the same horizontal line. What is the work done by the force of gravity on the object? Since the body returns to a point which is on the same horizontal line through the point of projection, no displacement has taken place against the force of gravity, therefore, no work is done by the force due to gravity. Q3. A battery lights a bulb. Describe the energy changes involved in the process. Within the electric cell of the battery the chemical energy changes into electrical energy. The electric energy on flowing through the filament of the bulb, first changes into heat energy and then into the light energy. [10/12, 6:53 PM] Anshuman: Q5. A mass of 10 kg is at a point A on a table. It is moved to a point B. If the line joining A and B is horizontal, what is the work done on the object by the gravitational force? Explain your answer. The work done is zero. This is because the gravitational force and displacement are perpendicular to each other. Q6. The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why? It does not violate the law Of conservation of energy. Whatever, is the decrease in PE due to loss of height, same is the increase in the KE due to increase in velocity of the body. Q7. What are the various energy transformations that occur when you are riding a bicycle? The chemical energy of the food changes into heat and then to muscular energy. On paddling, the muscular energy changes into mechanical energy Q8. Does the transfer of energy take place when you push a huge rock with all your might and fail to move it? Where is the energy you spend going? Energy transfer does not take place as no displacement takes place in the direction of applied force. The energy spent is used to overcome inertia of rest of the rock.
[12/11, 7:55 PM] Anshuman: Which party had been ruling Haryana since 1982? Ans. The Congress party had been ruling Haryana since 1982. 2. Who was Chaudhary Devilal? Name the party formed by him. Ans. Chaudhary Devilal was an opposition leader. He formed a new party called the Lok Dal, 3. Which promises of Devilal draw in election campaign attracted the people? Ans. He promised to waive the loans of small farmers and small businessmen. 4. What was the result of the elections in Haryana in 1987? Ans. Lok Dal and its partners won 76 out of 90 seats, with Lok Dal alone winning 60 seats. The Cong could win only 5 seats. 5. Why did the Chief Minister resign? Ans. His party lost the elections. Only the leader of the majority party can form a government. 6. Why do we have representatives in most democracies? Ans. In most democracies people rule through their representatives because it is not possible for ever to have time and knowledge to take decisions on all matters. [12/11, 7:55 PM] Anshuman: 21 What is a voters' list? 23. What is the Photo Identity Card System? Ans. Every voter is issued a photo Identity Card by the Election Commission. The voters are requ carry this card when they go out to vote, so that no one can vote for someone else, 24. Anyone who can be a voter can also become a candidate in elections, but there is Ans. In order to be a candidate in election the minimum age is 25 years, while it is only 18 ye What is it? one diffe being a voter. 25. What is a party ticket? Ans. Political parties nominate their candidates who get the party symbol and support. The pa nomination is also called the party ticket. 26. How does a person file his/her nomination papers? Ans. Every person who wishes to contest elections has to fill a nomination form and give some more "security deposit". This is how nomination papers are filed. 27. What are the legal declarations made by every party candidate? Ans. Details of assets and liabilities of the candidate and his or her family and educational qualific of the candidate. 28. Why has personal information of a candidate to be made public? Ans. The personal information of a candidate needs to be made public as it provides an opportun the voters to make their decisions on the of the information provided by the candidates 29. What is the main purpose of election? Ans. It is to give the people a chance to choose the representatives, the government and the policies prefer. 30. Why are election campaigns needed? Ans. The main purpose of elections is to give people a chance to choose their representatives government and the policies they prefer. Therefore it is necessary to have a free and open disco about which is better government or what is a good policy. It is possible during election campaign 31. What is the time period of campaigning for elections? Ans. In our country such campaigns take place for a two-week period between the announcement of final list of candidates and the date of polling. 32. How do the candidates attract the public during election? Ans. Political leaders address election meetings and political parties mobilise their supporters. Campai is also done through newspapers and television. Nowadays, the campaigning is also done th social media. Political parties try to focus public attention on some big issues. 33. Mention any two slogans given by different parties in various elections. Ans. (a) Garbi Hatao (Remove poverty), slogan of the Congress party led by Indira Gandhi in the elections. (b) Save Democracy was the slogan given by Janata Party under the leadership of Jaya Narayan in 1977 Lok Sabha elections.
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[09/11, 6:34 PM] ABHIJIT: Protons, electrons and neutrons have different properties like different charge, mass and stability. Protons are positively charged particles. Electrons are negatively charged particles. Neutrons are neutral particles which mean that they have no charge. [09/11, 6:35 PM] ABHIJIT: Thomson's atomic model failed to explain how the positive charge holds on the electrons inside the atom. It also failed to explain an atom's stability. The theory did not mention anything about the nucleus of an atom. [09/11, 6:36 PM] ABHIJIT: The major limitations of Rutherford’s model of the atom are: It does not explain the stability of the atom. As we know now, when charged bodies move in a circular motion, they emit radiations. This means that the electrons revolving around the nucleus (as suggested by Rutherford) would lose energy and come closer and closer to the nucleus, and a stage will come when they would finally merge into the nucleus. This makes the atom unstable, which is clearly not the case. The electrons do not fall into the nucleus, atoms are very stable and do not collapse on their own. [09/11, 6:37 PM] ABHIJIT: According to Bohr Atomic model, a small positively charged nucleus is surrounded by revolving negatively charged electrons in fixed orbits. He concluded that electron will have more energy if it is located away from the nucleus whereas the electrons will have less energy if it located near the nucleus. [09/11, 6:40 PM] ABHIJIT: J. J. Thomson's atomic model: [09/11, 6:40 PM] ABHIJIT: According to J. J. Thomson, electrons are contained within a sphere of positive charge. Rutherford's -particle scattering experiment, in which the majority of the rapid -particles traveled right through the gold foil, cannot be explained by Thomson's concept of the atom. [09/11, 6:40 PM] ABHIJIT: E.Rutherford's atomic model: According to Rutherford's gold foil studies, all of the positive charges are concentrated in a relatively small area that is 10 times the radius of one atom. [09/11, 6:41 PM] ABHIJIT: Neil Bohr's atomic model: Bohr proposed that electrons move about the nucleus in orbits with defined energy shells to account for the stability of an atom and atomic spectra.
[14/11, 8:12 PM] ABHIJIT: [14/11, 7:43 PM] Anshuman: Define the term 'work'. State the SI unit of work. Work is said to be done when a force displaces an object through a certain distance in the direction of the force. The SI unit of work is newton metre (Nm) also known as joule (J) in honour of the physicist James Joule. Define 1 joule. 1 J is the amount of work done on an object when a force of 1 N displaces the object through 1m in the direction of the force. 1 joule = 1 newton x 1 metre. A boy tries to push a truck parked on the roadside. The truck does not move at all. Another boy pushes a bicycle. The bicycle moves through a certain distance. In which case was the work done more : on the truck or on the bicycle? Give a reason to support your answer. The work done was more on the bicycle. Work done depends on force and displacement. Since the bicycle gets displaced and the truck does not, more work is done on the bicycle than the truck. How much work is done when a body of mass m is raised to a height h above the ground? Work done when a body of mass m is raised to a height h above the ground is given by "mgh". Is it possible that a force is acting on a body but sill the work done is zero? Explain giving one example. A force does not work if (a) The displacement is perpendicular to the force applied and (b) Applied force does not produce any displacement. Eg. (i) Earth is moving round the sun is almost circular orbit. In this case, the gravitational force is along the radius of the orbit while the instantaneous motion is tangential. As force and displacement are perpendicular to each other, the net work done is zero. (ii) A boy pushes the wall but the wall does not move. Hence, work done is zero. Complete the following sentence: The work done on a body moving in a circular path is The work done on a body moving in a circular path is zero. [14/11, 7:43 PM] Anshuman: How much work is done by the gravitational force of earth acting on a satellite moving around it in a circular path? Give reason for your answer. Earth is moving round the sun in almost circular earth Force orbit. In this case, the gravitational force is along the radius of the orbit while the instantaneous motion is tangential. As force and displacement are perpendicular to each other, the net work. done is zero. Sun instantaneous motion When is the work done by a force on a body: (a) positive, (b) negative, and (c) zero? (a) When the force and displacement are in the same direction, work done is positive. (b) When the force and displacement are in the opposite directions, work done is negative. (c) Work done is zero when, the displacement is perpendicular to the force applied or when applied force does not produce any displacement. A boy throws a rubber ball vertically upwards. What type of work, positive or negative, is done : (a) by the force applied by the boy? (b) by the gravitational force of earth? (a) Positive work.. (b) Negative work.. Robomate + Energy Define the term 'energy' of a body. What is the SI unit of energy? Is energy a vector quantity? What are the various forms of energy? The capability of an object to do work is known as energy. The SI unit of energy is joule (J). No, it is not a vector quantity. Energy exists in many different forms. The various forms of energy include mechanical energy, heat energy, chemical energy, electrical energy, light energy, sound energy, etc. What do you understand by the kinetic energy of a body? Energy possessed by an object by virtue of its motion is called kinetic energy (E). By how much will the kinetic energy of a body increase if its speed is doubled? If the speed of an object is doubled, its kinetic energy increases by 4 times. What is meant by potential energy? Write down the expression for gravitational potential energy of a body of mass m placed at a height h above the surface of the earth. The energy possessed by an object by virtue of its position or configuration is called as potential energy. The gravitational potential energy of a body of mass m at a height h above the surface of the earth is given by mgh. [14/11, 7:46 PM] Anshuman: State and explain the law of conservation of energy with an example. (i) Law of conservation of energy states that, "Energy can neither be created nor be destroyed. It can only be transformed from one form to the other. The total amount of energy in the universe always remains constant. (ii) Consider a simple example. Let an object of mass 'm' be made to fall freely from a height 'h'. (iii) At the start, the potential energy is mgh while the kinetic energy is zero. It is zero because the velocity is zero. (iv) The total energy of the object is thus mgh (mgh + 0) . As it falls, its potential energy changes into kinetic energy. If v ^ prime is the velocity at any instant, the kinetic energy would be 1/2 * m * v ^ 2 (v) As the fall of the object continues, the potential energy decreases while kinetic energy increases. (vi) When the object is about to touch the ground, h = 0 and v will be highest. Thus, potential energy is the least (zero) while kinetic energy is maximum. (vii) However at all points, the sum of kinetic and potential energies would be the 1 same. Thus, E+E= constant or mgh+ mv² = constant The hanging bob of a simple pendulum is displaced to one extreme position B and then released. It swings towards centre position A and then to the other extreme position C. In which position does the bob have: (i) maximum potential energy? (ii) maximum kinetic energy? Give reasons for your answer. Robomate + (i) Positions B and C (ii) Position A. Type A W = Fs Moon is experiencing a gravitational force due to earth is revolving around the earth in a circular orbit. How much work is done by moon? Moon revolving in a circular path is always directed along the tangent to a circular orbit. The angle between the line of action of force and displacement is 90 deg As cos 90 deg = 0 Work done = Fs cos 90 deg = 0 Therefore work done is zero. A 40 kg girl is running along a circular path of radius 1 m with a uniform speed. How much work is done by the girl in completing one circle ? Zero because displacement is zero. direction. Calculate the work done when a force of 15 N moves a body by 5 m in its Given F=15 N. s = 5m Using W = Fs = 15 * 5 = 75J [15/11, 11:09 AM] ABHIJIT: K
[22/11, 8:01 PM] Anshuman: 12. If bromine atom is available in the form of, say, two isotopes 35Br79 (49.7%) and 35Br81 (50.3%), calculate the average atomic mass of Bromine atom. Solution: The atomic mass of an element is the mass of one atom of that element. Average atomic mass takes into account the isotopic abundance. Isotope of bromine with atomic mass 79 u = 49.7% Therefore, Contribution of 35Br79 to atomic mass = (79 × 49.7)/100 ⇒ 39.26 u Isotope of bromine with atomic mass 81 u = 50.3% Contribution of 35Br81 to the atomic mass of bromine = (81 × 50.3)/100 ⇒ 40.64u Hence, average atomic mass of the bromine atom = 39.26 + 40.64 u = 79.9u 13. The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes 8X16 and 8X18 in the sample? Solution: Let the percentage of 8X16 be ‘a’ and that of 8X18 be ‘100-a’. As per given data, 16.2u = 16 a / 100 + 18 (100-a) /100 1620 = 16a + 1800 - 18a 1620 = 1800 - 2a a = 90% Hence, the percentage of isotope in the sample 8X16 is 90% and that of 8X18 = 100-a = 100- 90=10% 14. If Z=3, what would be the valency of the element? Also, name the element. Solution: Given: Atomic number, Z = 3 The electronic configuration of the element = K-2; L-1, hence its valency = 1 The element with atomic number 3 is Lithium. 15. Composition of the nuclei of two atomic species X and Y are given as under X Y Protons = 6 6 Neutrons = 6 8 Give the mass numbers of X and Y. What is the relation between the two species? Solution: Mass number of X: Protons + neutrons = 6+6 = 12 Mass number of Y: Protons + neutrons = 6+8 = 14 They are the same element as their atomic numbers are the same. They are isotopes as they differ in the number of neutrons and hence their mass numbers. 16. For the following statements, write T for true and F for false. (a) J.J. Thomson proposed that the nucleus of an atom contains only nucleons. (b) A neutron is formed by an electron and a proton combining together. Therefore it is neutral. (c) The mass of an electron is about 1/2000 times that of proton. (d) An isotope of iodine is used for making tincture iodine, which is used as a medicine. Solution: (a) Statement is False (b) Statement is False (c) Statement is True (d) Statement is False 17. Put a tick(✓) against correct choice and cross(x) against wrong choice in questions 15, 16 and 17. Rutherford’s alpha - particle scattering experiment was responsible for the discovery of (a) Atomic nucleus (b) Electron (c) Proton (d) Neutron Solution: (a) Atomic nucleus Isotopes of an element have (a) The same physical properties (b) Different chemical properties (c) Different number of neutrons (d) Different atomic numbers. Solution: (c) Different number of neutrons 18. Number of valence electrons in Cl- ion are: (a) 16 (b) 8 (c) 17 (d) 18 Solution: (b) 8 Electronic distribution of Cl is K-2, L-8, M-7. Valence electrons are 7, hence chlorine gains one electron for the formation of Cl-. Therefore, its valency is 8. 19. Which one of the following is a correct electronic configuration of Sodium? (a) 2, 8 (b) 8, 2, 1 (c) 2, 1, 8 (d) 2, 8, 1 Solution: (d) 2, 8, 1 [22/11, 8:03 PM] ABHIJIT: By Z = 3, we mean that the atomic number of the element is 3. Its electronic configuration is 2, 1. Hence, the valency of the element is 1 (since the outermost shell has only one electron). Therefore, the element with Z = 3 is lithium. [22/11, 8:05 PM] ABHIJIT: Atomic mass=number of protons+number of neutrons Atomic mass of X = 6+6=12 Atomic mass of Y =6+8=14 Both X and Y have same atomic number but different atomic mass number so they are isotopes. [22/11, 8:08 PM] ABHIJIT: Rutherford's alpha-particle scattering experiment was responsible for the discovery of atomic nucleus. Nucleus contains most of the mass. Most of the atom has empty space.
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