CBSE 2022|पदार्थों का पृथक्करण -L5|Separation of Substances|Class 6 NCERT विज्ञान |8PM |Subhadra Mam

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)]

An electron with total energy E = 5.1 eV approaches a barrier of height U_(h) = 6.8 eV and thickness L = 750 pm. What percentage change in the transmission coefficient T occurs for a 1.0% change in (a) the barrier height, (b) the barrier thickness, and (c) the kinetic energy of the incident electron?

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:

Scienists are working hard to develop inclear fusion reactor Nocies of heavy hydrogen, _(1)^(2)H , known as deuteron and denoted by D , can be thought of as a candidate for fusion rector . The D-D reaction is _(1)^(2) H + _(1)^(2) H rarr _(2)^(1) He + n+ energy in the core of fasion reactor a gas of heavy hydrogen of _(1)^(2) H nucles and electrons is know as plasma . The nuclei move randonity in the reactor to take place Unally , the temperature in the reactor core are too ligh and to natrual will can be used to confine the to pleama for a time l_(0) before the particles by away from the case if n is the denasity (number volume ) of determines , the product nt_(0) is called Lavson number in one of the criteria , a reactor is termed successful if Lawson number is greater then 5 xx 10^(14) s//cm^(2) it may be helpfull to use the following botczmann constant lambda = 8.6 xx 10^(-5)eV//k, (e^(2))/(4 pi s_(0)) = 1.44 xx 10^(-9) eVm Assume that two deuteron nuclei in the core of fasion reactor at temperacture energy T are moving toward each other, each with kinectic energy 1.5 kT , whenn the seperation between them is large enogh to leglect coulomb potential energy . Also neglate any interaction from other particle in the core . The minimum temperature T required for them to reach a separation of 4 xx 10^(-15) m is in the range