A man fixes outside his house one evening a two metre high insulating slab carrying on its top a large aluminium sheet of area $1 m^{2}$ . Will he get an electric shock if he touches the metal sheet next morning?

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Solution

The man will get an electric shock. The discharging current in atmosphere charges the aluminium sheet, and a capacitor is formed between ground and the slab.

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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.)

Q. Answer the following: (a) The top of the atmosphere is at about 400 kV with respect tothe surface of the earth, corresponding to an electric field thatdecreases with altitude. Near the surface of the earth, the fieldis about 100 Vm–1. Why then do we not get an electric shock aswe step out of our house into the open? (Assume the house tobe a steel cage so there is no field inside!) (b) A man fixes outside his house one evening a two metre highinsulating slab carrying on its top a large aluminium sheet ofarea 1m2. Will he get an electric shock if he touches the metalsheet next morning? (c) The discharging current in the atmosphere due to the smallconductivity of air is known to be 1800 A on an average overthe globe. Why then does the atmosphere not discharge itselfcompletely in due course and become electrically neutral? Inother words, what keeps the atmosphere charged? (d) What are the forms of energy into which the electrical energyof the atmosphere is dissipated during a lightning?(Hint: The earth has an electric field of about 100 Vm–1 at itssurface in the downward direction, corresponding to a surfacecharge density = –10–9 C m–2. Due to the slight conductivity ofthe atmosphere up to about 50 km (beyond which it is goodconductor), about + 1800 C is pumped every second into theearth as a whole. The earth, however, does not get dischargedsince thunderstorms and lightning occurring continually allover the globe pump an equal amount of negative charge onthe earth.)

Q. A bird can sit on a bare wire and does not get an electric shock . But a man standing on the ground gets an electric shock .When he touches the same wire .Why?

Q. Two large metal sheets carrying electric current along their surface. If current per unit length of the sheet is

λ

. The magnetic field at a point

P

on the same side of the sheets is

Q. A large metal sheet carries an electric current along its surface . Current par unit length is

λ

. Magnetic field near the metal sheet is :

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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?

The man will get an electric shock. The discharging current in atmosphere charges the aluminium sheet, and a capacitor is formed between ground and the slab.

A man fixes outside his house one evening a two metre high insulating slab carrying on its top a large aluminium sheet of area $1 m^{2}$ . Will he get an electric shock if he touches the metal sheet next morning?