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Ask iit jee aieee pet cbse icse state board community Community Discussion Question: electric field and potential
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perin (26)

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the questions r as follows:

    
spt_001 (96)

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there will not b any electric field after r=R.
u can prove this using gauss law
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perin (26)

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can u prove it.??

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perin (26)

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q.2 three concentic conducting spherical shells of radius r1 r2 r3 and charges q1 q2 q3 resp. innermost and outermost shells are earthed. then,
a q3/q2 = -1/3
b q1 = -q2/4
c q3/q1 = 3
d q1+ q3 = -q2

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spt_001 (96)

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the graph ques
after r=R using gauss law the net charge enclosed is zero. hence no elec field
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spt_001 (96)

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as inner and outer are earthed they r at same potential.
hence potential diff between them is 0.
kq3/r3+kq2/r3+kq1/r3=kq3/r3+kq2/r2+kq1/r1
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neeraj_agarwal_1990 (909)

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when inner most and outermost shells are earthed...there POTENTIAL becomes 0...
now equate their potentials to 0 and get the answers

note:charge on the innermost and outer most spheres are changed but the charge on middle shell remains same....
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neeraj_agarwal_1990 (909)

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For the 1st Q...
consider a gaussian surface through the small thickness of the shell...since electric field lines can't pass through a conductor...E=0.
using gauss law...enclosed charge =0....so a charge -q is induced at the inside surface of shell...using conservation of charge on shell...charge on outermost surface is 0...
so there doesn't exist field outside R.

note: charge always resides on the surface of a conductor...
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