CBSE 2022|पदार्थों का पृथक्करण -L10|Separation of Substances|Class6 NCERT विज्ञान |8PM |Subhadra Mam

A mole is a collection of 6.022 xx 10^23 particles and the number 6.022 xx 10^23 is called Avogadro number. The mass of this number of atoms in an element is equal to its gram atomic mass and mass of this number of molecules in a compound is equal to its gram molecular mass. The volume occupied by this number of molecules of a gas at N.T.P is 22.4 L. When 6.022 xx 10^23 molecules of a substance are dissolved in 1L of solution, the solution is known as 1 molar volume. The mass of 10 molecules of naphthalene (C_(10)H_(8))

Two horizontal parallel conducting plates are kept at a separation d = 1.5 xx 10^(-2) m apart one above the other in air as shown in figure. The upper plate is maintained at a positive potential of 1.5 kV while the other plate is earthed which maintains it at zero potential. Calculate the number of electrons which must be attached to a small oil drop of mass m =4.9 xx 10^(-15) kg between the plates to maintain it at rest. Consider density of air is negligible in comparison with that ofoil. If the potential of above plate is suddenly changed to -l .5kV , what will be the initial acceleration of the charged drop? Also calculate the terminal velocity of the drop if its radius is r= 5.0 xx 10^(-6)m and the coefficient of viscosity of air is eta = 1.8 x 10--5 N-s//m^(2) [3,2g, 5.7 xx 10^(-5) m//s^(2)]

Read the following text and answer the following questions on the basis of the same: Band theory of solid: Consider that the Si or Ge crystal contains N atoms. Electrons of each atom will have discrete energies in different orbits. The electron energy will be same if all the atoms are isolated, i.e., separated from each other by a large distance. However, in a crystal, the atoms are close to each other (2 Å to 3 Å) and therefore the electrons interact with each other and also with the neighbouring atomic cores. The overlap (or interaction) will be more felt by the electrons in the outermost orbit while the inner orbit or core electron energies may remain unaffected. Therefore, for understanding electron energies in Si or Ge crystal, we need to consider the changes in the energies of the electrons in the outermost orbit only. For Si, the outermost orbit is the third orbit (n = 3), while for Ge it is the fourth orbit (n = 4). The number of electrons in the outermost orbit is 4 (2s and 2p electrons). Hence, the total number of outer electrons in the crystal is 4N. The maximum possible number of outer electrons in the orbit is 8 (2s + 6p electrons). So, out of the 4N electrons, 2N electrons are in the 2N s-states (orbital quantum number l = 0) and 2N electrons are in the available 6N p-states. Obviously, some p-electron states are empty. This is the case of well separated or isolated atoms. The energy of electrons of atoms of a substance will be same if: