An electrometer is charged to 3 kV. Then the electrometer is touched with a neutral metal ball, mounted on an isulating rod and then the metal ball is taken away and earthed The process is done for 10 times and finally the electrometer reads 1.5 kV. After this, at least how many times must the above process be repeated in order that the electrometer reads less than 1 kV?

Electrolysis is the process in which electrical energy is converted to chemical energy. In electrolytic cell, oxidation takes place at anode and reduction at cathode. Electrode process depends on the electrode taken for electrolysis. Amount of substance liberated at an electrode is directly propertional to the amount of charge passed through it. The mass of substance liberated at electrode is calculated using the following relation : m= ("ItE")/(96500) Here, E represents the equivalent mass and 96500 C is called the Faraday constant. Faraday (96500 C) is the charge of 1 mole electron, i.e., 6.023 xx 10^(23) electrons, it is used to liberate one gram equivalent of the substance. How many faradays are required to reduce 1 mol BrO_(3)^(-) to Br^(-) ?

Answer the following: (a) The top of the atmosphere is at about 400 kV with respect to the surface of the earth, corresponding to an electric field that decreases with altitude. Near the surface of the earth, the field is about 100 Vm^(-1) . Why then do we not get an electric shock as we step out of our house into the open? (Assume the house to be a steel cage so there is no field inside!) (b) A man fixes outside his house one evening a two metre high insulating slab carrying on its top a large aluminium sheet of area 1m^(2) . Will he get an electric shock if he touches the metal sheet next morning? (c) The discharging current in the atmosphere due to the small conductivity of air is known to be 1800 A on an average over the globe. Why then does the atmosphere not discharge itself completely in due course and become electrically neutral? In other words, what keeps the atmosphere charged? (d) What are the forms of energy into which the electrical energy of the atmosphere is dissipated during a lightning? (Hint: The earth has an electric field of about 100 Vm^(-1) at its surface in the downward direction, corresponding to a surface charge density = 10^(-9)C m^(-2) . Due to the slight conductivity of the atmosphere up to about 50 km (beyond which it is good conductor), about + 1800 C is pumped every second into the earth as a whole. The earth, however, does not get discharged since thunderstorms and lightning occurring continually all over the globe pump an equal amount of negative charge on the earth.)

There are three unchanged identical metallic spheres 1,2 and 3 each of radius r and are placed at the verticles of an equlilateral triangle of side d .A charged metallic sphere having equal q of same radius r is touched to sphere 1 after some time it is taken to the location of sphere 2 and is touched to it ,then it is taken far away form sphere 1,2,3 after that the sphere 3 is grounded the charge on sphere 3 is (neglect electrostatic induction by assuming d gt gt 2r)

Two plane parallel conducting plates 1.5xx10^(-2)m apart are help horizontally one aove the other in air. The upper plate is maintained at positive potential of 1.5 kV while the other plate is earthed. Calculate the number of electorns which must be attached to a small oil drop of mass 4.9xx10^(-15)"kg" between the plates to maintain it at rest. If the potential of upper plate is suddenly changed to -1.5 kV, what is the initial acceleration of the charged drop ? Also obtain the terminal velocity of the drop if its radius is 5xx10^(-6)m and coefficient of viscosity of air is 1.8xx10^(-5)N-s//m^(2) . Assuming that the density of air is negligible in comparison with that of oil.

In a photoelectric setup, a point source of light of power 3.2xx10^(-3) W emits monoenergetic photons of energy 5.0 eV. The source is located at a distance of 0.8 m from the center of a stationary metallic sphere of work function 3.0 eV and of radius 8.0xx10^(-3) m. The efficiency of photoelectron emission is 1 for every 10^(6) incident photons. Assume that the sphere is isolated and initially neutral and that photoelectrons are instantaneously swept away after emission. Q. It is observed that photoelectron emission stops at a certain time t after the light source is switched on. It is due to the retarding potential developed in the metallic sphere due to lift over positive charged. The stopping potential (V) can be represented as