Physics Class 12 NCERT Solutions: Chapter 2 Electrostatic Potential and Capacitance Part 16

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Gauss's law of electrostatic

Gauss's Law of Electrostatic

Q: 36. A small sphere of radius and charge is enclosed by a spherical shell of radius and charge. Show that if is positive, charge will necessarily flow from the sphere to the shell (when the two are connected by a wire) no matter what the charge on the shell is.

Answer:

According to Gauss’s law, the electric field between a sphere and a shell is determined by the charge on a small sphere. Hence, the potential difference,, between the sphere and the shell is independent of charge. For positive charge. For potential difference V is always positive.

Q: 37. Answer the following:

(A) The top of the atmosphere is at about 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. 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 . 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 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 aboutat its surface in the downward direction, corresponding to a surface charge density. Due to the slight conductivity of the atmosphere up to about 50 km (beyond which it is good conductor), about 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.)

Answer:

(A)We do not get an electric shock as we step out of our house because the original equipotential surfaces of open air changes, keeping our body and the ground at the same potential.

(B) Yes, the man will get an electric shock if he touches the metal slab next morning. The steady discharging current in the atmosphere charges up the aluminum sheet. As a result, its voltage rises gradually. The raise in the voltage depends on the capacitance of the capacitor formed by the aluminium slab and the ground.

(C) The occurrence of thunderstorms and lightning charges the atmosphere continuously. Hence, even with the presence of discharging current of, the atmosphere is not discharged completely. The two opposing currents are in equilibrium and the atmosphere remains electrically neutral.

(D) During lightning and thunderstorm, light energy, heat energy, and sound energy are dissipated in the atmosphere.

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