The atom consists of a heavy positively charged nucleus and negatively charged electrons moving around it. Rutherford realized that important information about the inner structure of atoms could be obtained by the study of collisions between on rushing a particles and the atoms of various materials forming the target. } E = K + U={1 \over {{n^2}}}\left( {{{2{\pi ^2}{k^2}m{Z^2}{e^4}} \over {{h^2}}}} \right) Using the energy equation From the third rule of Bohr’s, a photon is emitted when an electron makes a transition from a higher sate to a lower state. The electron is an elementary particle having a mass {m_e} \approx 9.1 \times {10^{ - 31}}kg and a charge -e, e being an elementary charge approximately equal to 1.60 \times {10^{ - 19}}C. The nuclear charge is equal to +Ze, where Z is the atomic number. An electron revolving rapidly around a nucleus must have a continual centripetal acceleration, and this acceleration would cause a continuous loss of energy by radiation. var m = now.getMinutes(); var month = ("0" + (now.getMonth() + 1)).slice(-2); Author(s): NA. Similar Books. v = {{2\pi kZ{e^2}} \over {nh}} and r = {{{n^2}{h^2}} \over {4{\pi ^2}kmZ{e^2}}}, The electron revolving around the nucleus has kinetic energy, k = {1 \over 2}m{v^2} = {m \over 2}{\left( {{{2\pi kZ{e^2}} \over {nh}}} \right)^2} = {{2{\pi ^2}{k^2}m{Z^2}{e^4}} \over {{n^2}{h^2}}}, U = {{k{e^2}} \over r} =- k{e^2}\left( {{{4{\pi ^2}kmZ{e^2}} \over {{n^2}{h^2}}}} \right) = {{ - 4{\pi ^2}{k^2}m{Z^2}{e^4}} \over {{n^2}{h^2}}}, Notice that the magnitude of potential energy is double the magnitude of kinetic energy. (n = 1) is known as the ground state. (E1 < E2 < E3 < …). U = 2E = -2K, 4. var day = ("0" + now.getDate()).slice(-2); Dronstudy provides free comprehensive chapterwise class 12 physics notes with proper images & diagram. Putting the values ofk = {\rm{ }}9 \times {10^9} Nm2/C2 Bohr showed that Planck's quantum idea was a necessary part of the atom and its inner mechanism; he introduced the idea of quantized energy levels and explained the emission or absorption of radiation as being due to the transition of an electron from one level to another. The whole apparatus was evacuated, so that the particles would not collide with air molecules. The atom contains Z electrons, their total charge being -Ze. While circling around these permitted orbits, the electrons do not emit any electromagnetic radiation, even though conventional electrodynamics holds that they should } {\rm{ v = }}{{\Delta E} \over h}{\rm{ =3}}{\rm{.29}} \times {\rm{1015 Z}}\left( {{1 \over {n_1^2}} - {1 \over {n_2^2}}} \right)Hz According to Bohr's theory s = checkTime(s); ... Concept Maps , Previous Years Solved Papers ( Upto 12 Years ). //var today = now.getFullYear()+"-"+(month)+"-"+(day); Download NCERT Books, Video Lectures ASK DOUBTS Start Discusssion Free JEE Test Series, Get the most advanced study material and top your exams. Bohr in defiance of the well - established laws of classical mechanics and electrodynamics, proposed the following postulates: 1. Wavelength of photon emitted for a transition from n2 to n1, {1 \over \lambda } = {R_\infty }{Z^2}\left[ {{1 \over {n_1^2}} - {1 \over {n_2^2}}} \right] Home ; Grade 12 ; Physics; Back to subjects. It requires 47.2 eV to excite the electron from second Bohr orbit to the third Bohr orbit. var now = new Date(); The respective wavelength is If a substance which gives a line emission spectrum is placed in a magnetic field, the lines of the spectrum get split up into a number of closely spaced lines n =\infty which is the ionized state of the atom, From the third rule of Bohr’s, a photon is emitted when an electron makes a transition from a higher sate to a lower state. where {R_\infty }= Rydberg constant = 1.097 \times {10^7}{m^{ - 1}}, The various transitions for the hydrogen atom are shown in the following figure. The basic idea of the experimental arrangement used by Rutherford in his studies was explained as follows: In this diagram zero energy level corresponds to Notes for Atomic Structure chapter of class 12 physics. The (arbitrary) zero of energy is taken as the energy of a stationary electron, infinitely far from the positive nucleus. This phenomenon is known as Zeeman effect. A transition of the atom to a higher energy level may occur as a result of absorption of a photon or as a result of a collision with another atom or a particle, say, an electron. m = checkTime(m); The above discussion may be summarized as follows: The atom consists of a heavy positively charged. document.write(''); The above discussion may be summarized as follows: Thus,\Delta E = 13.6 \times {5^2}\left( {{1 \over {{1^2}}} - {1 \over {{\infty ^2}}}} \right)= 340 eV Dividing the above equation by c = 3 \times {10^8} m/s, we get For example, an atom which is in an excited state with the energy E3 can return to the ground state either directly, by emitting a photon of frequency if (i < 10) { The size of the nucleus varies depending on Z from 10-13 cm to 10-12 cm. Revision Notes for CBSE Class 12 Physics – Free PDF Download Free PDF download of CBSE Class 12 Physics revision notes and short key-notes to score more marks in your exams, prepared by our expert Physics teachers from the latest edition of CBSE (NCERT) books. {1 \over \lambda } ={{3.29 \times {{10}^{15}}} \over {3 \times {{10}^8}}}\left[ {{1 \over {n_1^2}} - {1 \over {n_2^2}}} \right]\,\,m-1 separated by finite gaps) values: Excited states of the atom are unstable. This would be possible, Rutherford reasoned, if all the positive charge, along with most of the atomic mass, were concentrated in a very small central region which Rutherford called the atomic nucleus. Such large deflections required strong forces to be acting, such as those between very smaller charged particles very close together. Class 12 Physics Index Page Here, we have provided a complete list of chapters and subtopics discussed in the Class 12 National Council of Educational Research and Training textbook (NCERT). Grade 12; PRACTICE. E = K + U Physics Notes Class XII As Per CBSE (NCERT) Books Chapter Wise-Notes PDF ( Board Level ) ... earth’s magnetic field and magnetic elements. Bohr calculated that this emission of radiation would cause the electrons in an atom to lose all their energy and fall into the nucleus within a hundred - millionth of a second. Physics formulas for class 12 are one of the most effective tools that can help 12th standard students fetch high marks in their board examination and other competitive exams. 47.2{\rm{ }} = {\rm{ }}13.6{Z^2} \Delta E = 13.6{Z^2}{{12400} \over{\Delta E}} = {{12400} \over {340}} = 36.47{A^0} \Rightarrow Z = {\rm{ }}5, (b) To find DE34; n1 = 3; n2 = 4 5 Speed of light. This means that it can assume only discrete (i.e. L = {h \over {2\pi }} = {{6.63 \times {{10}^{ - 34}}} \over {2\pi }} = 1.056 \times {10^{ - 34}}J - s={{6.63 \times {{10}^{ - 34}}} \over {2\pi }}={{6.63 \times {{10}^{ - 34}}} \over {2\pi }}=1.056 \times {10^{ - 34}} J-s, Physics Chemistry Mathematics Biology Excited states of the atom are unstable. U = 2E = -680 eV Download / View book. 3.Electrons may jump from one orbit to another, in such case the difference in energy between the two states of motion is radiated as a photon whose frequency is determined by the quantum rule, For an electron orbiting in a hydrogen like atom, the necessary centripetal force is the electrostatic attraction between the negative electron and the massive, positively-charged nucleus 6 Interference ,Diffraction and Polarisation. var s = now.getSeconds(); 3 Waves in pipes and strings. As a model for even multielectron atoms, the Bohr picture is still useful. where m is the mass of electron and M is the mass of nucleus, 5. document.write(''); The correct description of the distribution of, Rutherford realized that important information about the inner structure of atoms could be obtained by the study of collisions between.

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