Shown in the figure are two point charges +Q and -Q inside the cavity of a spherical shell. The charges are kept near the surface of the cavity on opposite sides of the centre of the shell. If \sigma _{1} is the surface charge on the inner surface and Q1 net charge on it and \sigma _{2} the surface charge on the outer surface and Q2 net charge on it then :

 

  • Option 1)

    \sigma _{1}\neq 0,Q_{1\neq }0

    \sigma _{2}\neq 0,Q_{2 }\neq0

  • Option 2)

    \sigma _{1}\neq 0,Q_{1}=0

    \sigma _{2}\neq 0,Q_{2 }=0

  • Option 3)

    \sigma _{1}\neq 0,Q_{1}=0

    \sigma _{2}= 0,Q_{2 }=0

  • Option 4)

    \sigma _{1}= 0,Q_{1}=0

    \sigma _{2}= 0,Q_{2 }=0

 

Answers (2)

As we learnt in

if Electric field is variable -

\phi = \int \vec{E}\cdot d\vec{A}

-

 

 Inside the cavity net charge is zero

\therefore Q_1 = 0\: and \: \sigma_1 \neq 0

There is no effect of point charge and induced charge on the inner surface and the outer surface

\therefore Q_2 = 0\: and \: \sigma_2 = 0

 


Option 1)

\sigma _{1}\neq 0,Q_{1\neq }0

\sigma _{2}\neq 0,Q_{2 }\neq0

Incorrect

Option 2)

\sigma _{1}\neq 0,Q_{1}=0

\sigma _{2}\neq 0,Q_{2 }=0

Incorrect

Option 3)

\sigma _{1}\neq 0,Q_{1}=0

\sigma _{2}= 0,Q_{2 }=0

Correct

Option 4)

\sigma _{1}= 0,Q_{1}=0

\sigma _{2}= 0,Q_{2 }=0

Incorrect

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