CBSE 12th Standard Physics Subject Atoms Value Based Questions 5 Mark Questions With Solution 2021
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CBSE 12th Standard Physics Subject Atoms Value Based Questions 5 Mark Questions With Solution 2021
12th Standard CBSE
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Reg.No. :
Physics
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Nuclear fission is the phenomenon of splitting of a heavy nucleus into two or more lighter nuclei. Nuclear fussion is the phenomenon of fusing two or more lighter nuclei to form a single heavy nucleus. In both these processes, a certain mass \(\left( \Delta m \right) \) disappears, which appears in the form of nuclear energy, \(E=\left( \Delta m \right) { c }^{ 2 }.\) The release of energy is so sudden that it cannot be controlled. This causes havoc. Nuclear fission is the basis of an atom bomb and nuclear fusion is the basis of a nydrogen bomb. A powerful device, called Nuclear Reactor has been developed, where in nuclear energy produced is utilised for constructive purposes.
Read the above passage and answer the following questions:
(i) How much energy is released in the fission of one nucleus of \({ U }^{ 235 }\) and in how much time?
(ii) Give an estimate of devastation potential of an atomic explosion.
(iii) Should we ban nuclear research in this field? Give your views briefly.(a) -
Natural radioactivity is a spontaneous and self disruptive activity exhibited by a number of heavy elements in nature. Thus a heavy element disintegrates by itself without being forced by any external agent to do so.
According to radioactive decay law, the number of atoms disintegrated per second (i.e., rate of disintegration of radioactive atoms) at any instant is directly proportional to the number of radioactive atoms actually present in the sample at that instant, i.e., \(-\frac { dN }{ dt } \propto N \ or \ R=-\frac { dN }{ dt } =\lambda N,\) where is \(\lambda \) decay constant.
Read the above passage and answer the following questions :
(i) The count rate from a radioactive sample containing \({ 10 }^{ 16 }\) atoms is \(4\times { 10 }^{ 16 }\) per second. What is the value of decay constant?
(ii) Name the three types of radiactive radiations. Which one of them is most penetrating?
(iii) What does radioactive decay law imply in day to day life?(a) -
According to Bohr's theory of hydrogen atom, total energy of electron in a stationary orbit is \(E=-\frac { 13.6 }{ { n }^{ 2 } } eV,\) where n is the number of orbit. Clearly, total energy of electron in a stationary orbit is negative, which means the electron is bound to the nucleus and is not free to leave it. An n increases, value of negative energy decreases, i.e., energy is progressively larger in the outer orbits.
Read the above passage and answer the following questions :
(i) What is total energy of electron in ground state of hydrogen atom? What does it imply?
(ii) Energy required to remove an electron is smaller when atoms is in any one excited state. Comment.
(iii) How is this concept translated in day to day life?(a) -
Ajeet's younger brother was just seeing class 12th books. He wondered to know the structure of atoms and arrangement of electrons and protons in them. As he was a class 6th student, he did not understand the whole concept of atomic structure. Ajeet helped him to understand the structure of atoms.
Read the above passage and answer the following questions:
(i) What are the values shown by Ajeet?
(ii) On which metal Rutherford performed \(\alpha \) - particles scattering experiment?
(iii) How Rutherford concluded that at the centre of atom there is massive nucleus which contains positive charge?(a) -
On the basis of Bohr's theory of H-atom, total energy of electron in a stationary orbit is given by the relation
Where, n is the number of orbits. It is clear that total energy of electron in a stationary orbit is negative which implies that electron is bound to the nucleus and is not free to leave it. The value of negative energy decreases as n increases.
Read the above p[assagr and answer the following questions:
(i) What is the total energy of electron in ground state of hydrogen atom? What does it indicate?
(ii) Why does energy required to remove an electron is smaller when atom is in any one excited state?(a)
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CBSE 12th Standard Physics Subject Atoms Value Based Questions 5 Mark Questions With Solution 2021 Answer Keys
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(i) From the fission of a single nucleus of \(_{ 92 }{ { { U }^{ 235 } } }\); 200 MeV energy is released in \({ 10 }^{ -9 }\) second, i.e., almost instantly.
(ii) First atomic explosion occurred in 1945 when an atom bomb was dropped on the city of Hiroshima, Japan. This resulted in the killing of about 66000 people and grievous injury to an equal number. 2/3rd of city structures were smashed and so on.
(iii) No, the research must go on. But we must investigate ways and means for harnessing the enormous amount of nuclear energy for peaceful purposes. Nuclear reactor is an outcome of that research. -
(i) Here, \(N={ 10 }^{ 16 } \ and \ \frac { dN }{ dt } =4\times { 10 }^{ 16 } \ per \ sec.\lambda =?\)
\(From \ \frac { dN }{ dt } =\lambda N\)
\( \lambda =\frac { dN/dt }{ dt } =\frac { 4\times { 10 }^{ 16 } }{ { 10 }^{ 16 } } =4\times { 10 }^{ 16 }{ sec }^{ -1 }\)
(ii) The three types of radiactive are radiations are : \(\alpha \)-rays; \(\beta \)-rays and \(\gamma \)-rays. Out of then, \(\alpha \)-rays have maximum penetrating power.
(ii) Radioactive decay law is the law of mass action, i.e., larger the available mass, greater is its rate of decay. The same applies in day to day life. Larger the population, greater is their decay rate, i.e., death rate, i.e., under given conditions, when number of people is large, the rate at which they die is also large. The reverse is also true. -
(i) For ground state, n = 1
\(\therefore E=\frac { -13.6 }{ { n }^{ 2 } } eV= \ \frac { -13.6 }{ { I }^{ 2 } } eV= \ -13.6 \ eV\)
It implies that 13.6 eV energy is required to remove an electron from hydrogen atom in its ground state.
(ii) In first excited state, n = 2,
\(\therefore \ E=-\frac { 13.6 }{ { 2 }^{ 2 } } eV \ = \ -3.4eV\)
It means that energy required to remove an electron from hydrogen atom in first excited state is 3.4 eV, which is less than 13.6 eV. Therefore, the statement is true.
(iii) Negative energy of electron indicates that it is bound to the nucleus and cannot leave it until energy equal to its negative energy is supplied from outside. The same is true in day to day life. A person intending to leave the country has to show that nothing is pending against him in a court of law, and he has cleared income tax/sales tax payments due from him. A person from whom any type of payment is due, is not free to leave the country. He is bound till he clears all his dues. -
(i) Ajeet is intelligent, cooperative and has good command over Physics.
(ii) Rutherford used gold foil of 10-8m thickness.
(iii) When Rutherford was performing \(\alpha \) - particles scattering experiment, he observed that very less number of \(\alpha \) - particles retrace their path. Thus, he concluded that there is a positive massive part at the centre of atom and named it nucleus. -
(i) The total energy of electron in ground state (n = 1) is
\({ E }_{ 1 }=-\cfrac { 13.6 }{ { 1 }^{ 2 } } eV=-13.6eV\)
It indicates that 13.6eV energy is needed to remove an electron from hydrogen atom in its ground state.
(ii) Energy in first excited state(n = 2) is
\({ E }_{ 2 }=-\cfrac { 13.6 }{ { 2 }^{ 2 } } eV=-3.4eV\)
It implies that energy needed to remove an electron from hydrogen atom in first excited state is 3.4eV, which is less than 13.6eV.
