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Questions and Answers
What is the charge-to-mass ratio of an electron, as determined by Millikan's oil drop experiment?
Which subatomic particle was discovered by observing the deflection of canal rays in a magnetic field?
In the absence of an electric or magnetic field, which path do electrons follow?
Who discovered neutrons and what is their charge?
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Which experiment involved bombarding alpha particles with beryllium to discover neutrons?
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What is the formula to find the number of electrons in a particle given its charge?
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Which subatomic particle has a charge-to-mass ratio of approximately 3.72 x 10^3?
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What did Rutherford's gold foil experiment reveal about the atom?
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Which atomic model suggests that the atom is like a plum pudding?
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What does Maxwell's theory of electrodynamics predict about electrons in circular orbits?
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Study Notes
- The text is about a lecture on the structure of the atom, covered in Class 11th physics, with a focus on understanding topics for JEE Mains and Advanced exams.
- The lecture includes various topics, some of which are important for JEE exams, while others are foundational knowledge.
- The first topic covered is the discovery of subatomic particles, specifically electrons, protons, and neutrons.
- Discovery of subatomic particles occurred through experiments using a Cathode Ray Tube (CRT), which revealed the behavior of electrons.
- Electrons travel in straight lines in the absence of an electric or magnetic field but deflect when present.
- The characteristic of cathode rays is that they do not depend on the material of the electrodes or the gas inside the tube.
- Millikan's oil drop experiment demonstrated the charge-to-mass ratio of electrons (e/m = -1.602176 x 10^-19 C/kg).
- The lecture then moves on to the discovery of protons by observing the deflection of canal rays (anode rays) in a magnetic field.
- Protons have a positive charge and a mass approximately 1836 times that of electrons.
- Neutrons were discovered by Chadwick in 1932 and have a neutral charge and a mass almost identical to that of a proton.
- The lecture also covers the atomic models, including Thomson's and Rutherford's models, and various related concepts.- In 1932, alpha particles were discovered to emit neutrons when bombarded with beryllium.
- Alpha particles are subatomic particles with two positive charges and a mass of 4.
- Neutrons, which are neutral in nature but have mass, were observed being produced when alpha particles collided with beryllium.
- J.J. Thomson determined the ratio of charge to mass of an electron, which is approximately 1.76 x 10^8 coulombs per gram, by measuring deflections of cathode rays in electric and magnetic fields.
- To find the number of electrons in a particle carrying a charge of 5.5 x 10^-16 coulombs, use the formula n = Q/e, where n is the number of electrons, Q is the charge, and e is the charge of an electron (1.6 x 10^-19 coulombs).
- The charge-to-mass ratios of neutron, alpha particle, proton, and electron are 0, 3.72 x 10^3, 1, and 1.76 x 10^8, respectively. The particle with the greatest charge-to-mass ratio is the electron.- The speaker is discussing various concepts related to atomic structure, including atomic number, mass number, isotopes, isobars, and atomic models.
- Atomic number is the number of protons in the nucleus of an atom, denoted by the letter Z.
- Mass number is the total number of nucleons (protons and neutrons) in the nucleus, denoted by the letter A.
- Isotopes are atoms with identical atomic numbers but different mass numbers.
- Isobars are atoms with the same mass number but different atomic numbers.
- Thomson's atomic model suggests that the atom is like a plum pudding, with electrons embedded in a positively charged sphere.
- Rutherford's gold foil experiment revealed that the atom has a small, positive nucleus at its center, with most of the atom's volume being empty space.
- Electrons revolve around the nucleus in circular orbits, held together by electrostatic forces.
- Maxwell's theory of electrodynamics predicts that an electron in circular orbit should continuously emit energy, which could cause the atom to fall apart, but experimental evidence shows that this does not happen.
- The distance of closest approach refers to the point where an alpha particle comes closest to the nucleus before being deflected back.
- Kinetic energy is the energy of motion, and potential energy is the energy of position.
- The speaker mentions that the radius of the nucleus is much smaller than that of the atom, and the positive charge of the atom is concentrated in the nucleus.
- Thomson's atomic model is important historical background but has limitations, such as not being consistent with Maxwell's theory of electrodynamics.
- The speaker encourages the audience to learn about these concepts in more detail for exams like IIT-JEE and MSAT.
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Description
Explore the intricate details of the atomic structure discussed in a Class 11th physics lecture focusing on topics crucial for JEE Mains and Advanced exams. Learn about the discovery of subatomic particles like electrons, protons, and neutrons, Millikan's oil drop experiment, atomic models by Thomson and Rutherford, characteristics of cathode rays, isotopes, isobars, and more.
