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JEE Advanced 2015Paper 2
Exam
JEE Advanced
Year
2015
Paper
Paper 2
Subject
Physics
Chapter
Electrostatics

JEE Advanced 2015 · Paper 2 · Physics · Electrostatics

Consider a uniform spherical charge distribution of radius R _ 1...

Consider a uniform spherical charge distribution of radius R1{R}_{1} centred at the origin O. In this distribution, a spherical cavity of radius R2{R}_{2} , centred at PP with distance OP=a=R1−R2OP = a = {R}_{1} - {R}_{2} (see figure) is made. If the electric field inside the cavity at position r→\overset{\to}{r} is E→(r→)\overset{\to}{E} ( \overset{\to}{r} ) , then the correct statement(s) is (are)

Consider a uniform spherical charge distribution of radius R _ 1 centred at the origin O. In this distribution, a

Options

  1. AE→\overset{\to}{E} is uniform, its magnitude is independent of R2{R}_{2} but its direction depends on r→\overset{\to}{r}
  2. BE→\overset{\to}{E} is uniform, its magnitude is depends on R2{R}_{2} and its direction depends on r→\overset{\to}{r}
  3. CE→\overset{\to}{E} is uniform, its magnitude is dependent of a but its direction depends on a→\overset{\to}{a}
  4. DE→\overset{\to}{E} is uniform and both its magnitude and direction depend on a→\overset{\to}{a}

Correct answer

D. E→\overset{\to}{E} is uniform and both its magnitude and direction depend on a→\overset{\to}{a}

Step-by-step solution


Consider a uniform spherical charge distribution of radius R _ 1 centred at the origin O. In this distribution, a
Considering any point A inside the cavity electric field can be calculated at A by using super position principle.
{\overset{\to}{E}}_{A} = {\left({\overset{\to}{E}}_{A}\right)}_{Duetospherewithoutcavity} - {\left({\overset{\to}{E}}_{A}\right)}_{Duetosphereofradius{R}_{2} & centreatP}
E→A=ρ3ϵ0OA→=ρ3ϵ0(PA→){\overset{\to}{E}}_{A} = \dfrac{ρ}{3{ϵ}_{0}}O\overset{\to}{A} = \dfrac{ρ}{3{ϵ}_{0}}\left(P\overset{\to}{A}\right)
But OP→+PA→=OP→O\overset{\to}{P} + P\overset{\to}{A} = O\overset{\to}{P}
∴OA→−PA→=OP→∴ O\overset{\to}{A} - P\overset{\to}{A} = O\overset{\to}{P}
∴E→A=ρ3ϵ0(OP→)=ρ3ϵ0(a→)∴ {\overset{\to}{E}}_{A} = \dfrac{ρ}{3{ϵ}_{0}}\left(O\overset{\to}{P}\right) = \dfrac{ρ}{3{ϵ}_{0}}\left(\overset{\to}{a}\right)
So E.F. is independent of location of A inside the cavity.
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