Login/Sign Up
Answer the following: (a) The top of the atmosphere is at about $400 \mathrm{kV}$ 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 $100 \mathrm{Vm}^{-1}$. 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 $1 \mathrm{~m}^{2} .$ Will he get an electric shock if he touches the metal sheet the next morning? (c) The discharging current in the atmosphere due to the small conductivity of air is known to be 1800 A on 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 lightning? (Hint: The earth has an electric field of about $100 \mathrm{Vm}^{-1}$ at its surface in the downward direction, corresponding to a surface charge density $=-10^{-9} \mathrm{C} \mathrm{m}^{-2} .$ Due to the slight conductivity of the atmosphere up to about $50 \mathrm{~km}$ (beyond which it is good conductor), about + $1800 \mathrm{C}$ 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.)
Answer the following:
(a) The top of the atmosphere is at about $400 \mathrm{kV}$ 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 $100 \mathrm{Vm}^{-1}$. 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 $1 \mathrm{~m}^{2} .$ Will he get an electric shock if he touches the metal sheet the next morning?
(c) The discharging current in the atmosphere due to the small conductivity of air is known to be 1800 A on 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 lightning?
(Hint: The earth has an electric field of about $100 \mathrm{Vm}^{-1}$ at its surface in the downward direction, corresponding to a surface charge density $=-10^{-9} \mathrm{C} \mathrm{m}^{-2} .$ Due to the slight conductivity of the atmosphere up to about $50 \mathrm{~km}$ (beyond which it is good conductor), about + $1800 \mathrm{C}$ 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.)
CBSE | Class 12 | Electrostatic Potential and Capacitance | NCERT | Physics
Answer the following:
(a) The top of the atmosphere is at about $400 \mathrm{kV}$ 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 $100 \mathrm{Vm}^{-1}$. 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 $1 \mathrm{~m}^{2} .$ Will he get an electric shock if he touches the metal sheet the next morning?
(c) The discharging current in the atmosphere due to the small conductivity of air is known to be 1800 A on 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 lightning?
(Hint: The earth has an electric field of about $100 \mathrm{Vm}^{-1}$ at its surface in the downward direction, corresponding to a surface charge density $=-10^{-9} \mathrm{C} \mathrm{m}^{-2} .$ Due to the slight conductivity of the atmosphere up to about $50 \mathrm{~km}$ (beyond which it is good conductor), about + $1800 \mathrm{C}$ 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.)

(a) The surface formed by our bodies and the ground is an equipotential surface. As soon as we go out into the open, the original equipotential surfaces of open-air shift, maintaining the same potential between our head and the surrounding ground.

(b) In a word, yes. Due to the constant discharge current in the atmosphere, a gradual charge up of the aluminium sheet occurs, which raises the voltage to a degree that is determined by the capacitance of the capacitor (formed by the sheet, slab and the ground).

(c) Thunderstorms and lightning strike all around the world, constantly charging the atmosphere, which is then discharged through regions of normal weather. On average, the two opposing currents are in equilibrium with one another.

(d) The light energy emitted by lightning, as well as the heat and sound energy emitted by the accompanying thunder.

i

More Material