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 1m2.
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.)
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 1m2. 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.)
(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 aluminium 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 1800 A, 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.
(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 aluminium 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 1800 A, 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.
