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NCERT Exemplar Class 12 Physics solutions chapter 12 deals with the fundamental building blocks of any material that exists in this Universe. The term "atom" comes from the Greek word "atomos," which means indivisible because it was considered that atoms were the smallest things and could not be divided further. NCERT Exemplar Class 12 Physics chapter 12 solutions discuss the atomic particles inside the atom, namely protons, electrons, and neutrons. The nucleus is the central sphere of the atom, which contains the protons (positively charged) and the neutrons (no charge). The atom's outermost region is called an electron shell, which includes the electrons (negatively charged).
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As we learn about atoms and their structure, we would find that we start from minute particles and achieve something substantial. Class 12 Physics NCERT Exemplar solutions chapter 12 given on this page would help you understand the concepts from scratch and NCERT is helpful for the 12 boards or competitive exams. NCERT Exemplar Class 12 Physics solutions chapter 12 PDF download is also available for students, for further learning. The topics and subtopics covered are as follows:
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Question:1
Taking the Bohr radius as a0 = 53pm, the radius of Li++ ion in its ground state, on the basis of Bohr’s model, will be about
A. 53 pm
B. 27 pm
C. 18 pm
D. 13 pm
Answer:
The answer is the option (c).Question:2
The binding energy of a H-atom, considering an electron moving around a fixed nuclei (proton), is
. (m = electron mass). If one decides to work in a frame of reference where the electron is at rest, the proton would be moving around it. By similar arguments, the binding energy would be
(M = proton mass)
This last expression is not correct because
A. n would not be integral.
B. Bohr-quantization applies only to electron
C. the frame in which the electron is at rest is not inertial.
D. the motion of the proton would not be in circular orbits, even approximately.
Answer:
The answer is the option (c) the frame in which the electron is at rest is not inertial.Question:3
The simple Bohr model cannot be directly applied to calculate the energy levels of an atom with many electrons. This is because
A. of the electrons not being subject to a central force.
B. of the electrons colliding with each other
C. of screening effects
D. the force between the nucleus and an electron will no longer be given by Coulomb’s law.
Answer:
The answer is the option (a).Question:4
For the ground state, the electron in the H-atom has an angular momentum =? according to the simple Bohr model. Angular momentum is a vector, and hence there will be infinitely many orbits with the vector pointing in all possible directions. In actuality, this is not true,
A. because Bohr model gives incorrect values of angular momentum.
B. because only one of these would have a minimum energy.
C. angular momentum must be in the direction of spin of electron.
D. because electrons go around only in horizontal orbits.
Answer:
Option (a) is the correct answer as -Question:5
O2 molecule consists of two oxygen atoms. In the molecule, nuclear force between the nuclei of the two atoms
A. is not important because nuclear forces are short-ranged.
B. is as important as electrostatic force for binding the two atoms.
C. cancels the repulsive electrostatic force between the nuclei.
D. is not important because oxygen nucleus have equal number of neutrons and protons.
Answer:
The answer is the option (a).Question:6
Two H atoms in the ground state collide in-elastically. The maximum amount by which their combined kinetic energy is reduced is
A. 10.20 eV
B. 20.40 eV
C. 13.6 eV
D. 27.2 eV
Answer:
The answer is the option (a).Question:7
A set of atoms in an excited state decays.
A. in general to any of the states with lower energy.
B. into a lower state only when excited by an external electric field.
C. all together simultaneously into a lower state.
D. to emit photons only when they collide.
Answer:
A set of atoms in an excited state decays in general to any of the states with lower energy.Question:8
An ionized H-molecule consists of an electron and two protons. The protons are separated by a small distance of the order of angstrom. In the ground state,
A. the electron would not move in circular orbits.
B. the energy would be (2)4 times that of an H-atom.
C. the electrons, the orbit would go around the protons.
D. the molecule will soon decay in a proton and an H-atom.
Answer:
The correct answers are the options (a, c). The electron present in the hydrogen atom revolves in a circular path around a fixed nucleus. This easily explained by the Bohr’s model. But the Bohr’s model cannot explain the protonated structure of hydrogen atom when t contains two protons around the nucleus separated by a small distance in the same order of angstrom. So, in this ground state scenario, the electrons orbit will go around the protons instead of moving in their usual circular path around the nucleus.Question:9
Consider aiming a beam of free electrons towards free protons. When they scatter, an electron and a proton cannot combine to produce a H-atom,
A. because of energy conservation.
B. without simultaneously releasing energy in the form of radiation.
C. because of momentum conservation.
D. because of angular momentum conservation.
Answer:
The correct answers are the options (a, b). Due to the law of conservation of energy, a moving electron and a proton cannot collectively form a hydrogen atom as they will simultaneously release energy in the form of radiation.Question:10
The Bohr model for the spectra of a H-atom
A. will not be applicable to hydrogen in the molecular from.
B. will not be applicable as it is for a He-atom.
C. is valid only at room temperature.
D. predicts continuous as well as discrete spectral lines.
Answer:
The correct answers are the options (a, b). The model of the atom proposed by Neil Bohr was applicable for the hydrogen atom and some other light atoms containing only one electron around the nucleus which is stationary having a positive charge, Ze (called a hydrogen-like atom, e.g., H, He+, Li+2, Na+1 etc). But one of the limitations of the model is that it is not applicable to hydrogen in its molecular form and also in case of He atom.Question:11
The Balmer series for the H-atom can be observed
A. if we measure the frequencies of light emitted when an excited atom falls to the ground state.
B. if we measure the frequencies of light emitted due to transitions between excited states and the first excited state.
C. in any transition in a H-atom.
D. as a sequence of frequencies with the higher frequencies getting closely packed.
Answer:
The correct answers are the options (b, d) is the correct option as,Question:12
Let be the energy of the nth level of H-atom. If all the H-atoms are in the ground state and radiation of frequency (E2-E1)/h falls on it,
A. it will not be absorbed at all
B. some of atoms will move to the first excited state.
C. all atoms will be excited to the n = 2 state.
D. no atoms will make a transition to the n = 3 state.
Answer:
The correct answers are the options (b, d). Let us assume E2 and E2 as the energy corresponding to n = 2 and n = 1 respectively. According to the Bohr’s model of atom few of the atoms will reach to the first excited state if the radiation of energy on a sample in which all the hydrogen atoms at ground state is E = (E2 – E1) = hf incident. But as the energy is insufficient for the transition to take place from n = 1 to n =3, therefore none of the atoms present will reach up to the n = 3 state.Question:13
The simple Bohr model is not applicable to atom because
A. is an inert gas.
B. has neutrons in the nucleus.
C. has one more electron.
D. electrons are not subject to central forces.
Answer:
The correct option of the mentioned problem is (c), (d) as,Question:14
The mass of an H-atom is less than the sum of the masses of a proton and electron. Why is this?
Answer:
Mass defect: It is found in that the mass of the nucleus is always less than the masses of its constituent nucleons in a free state. This difference in masses is called the mass defect. Hence mass defectQuestion:15
Answer:
One of the biggest limitations of the Bohr’s model of the atom is that it is only applicable for either light atoms having one electron revolving around the nucleus or for H-atoms. The nucleus of these atoms must be positively charged and stationery, such atoms are termed as Ze (called hydrogen-like atom). But if one electron is removed from both He4 and He3, they will fulfil the condition, and the model can be used to find their energy levels.Question:17
Answer:
Neil Bohr proposed that if an electron is moving around a stationary nucleus, the require centripetal force is provided by the electrostatic force of attraction.Question:18
Answer:
According to Bohr model electrons having different energies belong to different levels having different values of n. So, their angular momenta will be different, asQuestion:19
Answer:
The total energy of the electron in the stationary states of the hydrogen atom is given byQuestion:21
Answer:
The equivalent electric current due to rotation of charge is given byQuestion:22
Answer:
Frequency of emitted radiation:Question:23
Answer:
“H-alpha” that corresponds to transition 3 -> 2. And “H-beta” corresponds to 4 -> 2 and the “H-gamma” corresponds to transition 5 -> 2.Question:24
Answer:
Let us take as the reduced masses of electron of hydrogen and as the reduced masses of electron of deuterium.Question:25
Answer:
According to Bohr’s theory for a hydrogen-like atom of atomic number Z, the total energy of the electron in the nth state isQuestion:26
Answer:
The electron present in H-atom revolves around the point size proton of a defined radius rB (Bohr’s radius) in a circular path when the atom is in the ground state.Question:27
Answer:
Auger Effect: While responding to the downward transition by another electron in the atom, the characteristic energies of the atoms are ejected, and this process is called Auger effect. The bombardment with the high energy electrons results in the formation of a vacancy in Auger spectroscopy. But the effect is possible when other interaction leads to vacancy formation. It is an electron arrange method after the nucleus captures the electron.Question:28
The inverse square law in electrostatics is for the force between an electron and a proton. The dependence of |F| can be understood in quantum theory as being due to the fact that the ‘particle’ of light (photon) is massless. If photons had a mass mp, force would be modified to where and .
Estimate the change in the ground state energy of a H-atom if mp were 10–6 times the mass of an electron.
Answer:
We are givenQuestion:29
The Bohr model for the H-atom relies on the Coulomb’s law of electrostatics. Coulomb’s law has not directly been verified for very short distances of the order of angstroms. Supposing Coulomb’s law between two opposite charge +q1, –q2 is modified to
Calculate in such a case, the ground state energy of an H-atom, if
Answer:
Let the case consider the case whenClass 12 Physics NCERT Exemplar solutions chapter 12 explores the different atoms' different models over time and the experiments that led to discovering atomic particles. NCERT Exemplar solutions for Class 12 Physics chapter 12 will also throw light on the other characteristics and properties of elements depending on the atomic particles' location and number. We study atoms because the Universe revolves around the properties of elements, not necessarily the properties of an electron or proton.
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One can learn about atoms, their properties, various atomic models, Bohr’s model, line spectra, alpha particle trajectory in detail.
These questions are solved in an exhaustive manner, so as to cover every step and every detail for students' better grasping in NCERT exemplar Class 12 Physics solutions chapter 12 Atoms
Yes, these solutions can help in understanding the topic better and thus get a good grip on topics for entrance exams.
These Class 12 physics NCERT exemplar solutions chapter 12 can help in checking one's answers after solving them, understanding the details, and preparing in a better way.
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If you have uploaded screenshot of your 12th board result taken from CBSE official website,there won,t be a problem with that.If the screenshot that you have uploaded is clear and legible. It should display your name, roll number, marks obtained, and any other relevant details in a readable forma.ALSO, the screenshot clearly show it is from the official CBSE results portal.
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Hello Akash,
If you are looking for important questions of class 12th then I would like to suggest you to go with previous year questions of that particular board. You can go with last 5-10 years of PYQs so and after going through all the questions you will have a clear idea about the type and level of questions that are being asked and it will help you to boost your class 12th board preparation.
You can get the Previous Year Questions (PYQs) on the official website of the respective board.
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