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A charge Q is uniformly distributed over a long rod AB of length L as shown in the figure. The electric potential at the point O lying at a distance L from the end A is

  • fraction numerator straight Q over denominator 8 πε subscript straight o straight L end fraction
  • fraction numerator 3 space straight Q over denominator 4 space πε subscript straight o straight L end fraction
  • fraction numerator straight Q over denominator 4 πε subscript straight o straight L space In space 2 end fraction
  • fraction numerator straight Q over denominator 4 πε subscript straight o straight L space In space 2 end fraction


D.

fraction numerator straight Q over denominator 4 πε subscript straight o straight L space In space 2 end fraction

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This question has statement 1 and statement 2. Of the four choices given after the statements, choose the one that best describes the two statements.
An insulating solid sphere of radius R has a uniformly positive charge density ρ. As a result of this uniform charge distribution, there is a finite value of the electric potential at the centre of the sphere, at the
surface of the sphere and also at a point out side the sphere. The electric potential at infinity is zero.
Statement 1: When a charge q is taken from the centre to the surface of the sphere, its potential energy changes by qρ/3εo
Statement 2: The electric field at a distance r(r < R) from the centre of the sphere is  ρr/3εo

  • Statement 1 is true, Statement 2 is true, Statement 2 is not the correct explanation for statement 1.

  • Statement 1 is true, Statement 2 is false

  • Statement 1 is false, Statement 2 is true

  • Statement 1 is false, Statement 2 is true


C.

Statement 1 is false, Statement 2 is true


Statement 2 is correct

statement 1 is incorrect.
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Let there be a spherically symmetric charge distribution with charge density varying as  space straight rho left parenthesis straight r right parenthesis space equals space space straight rho subscript 0 space open parentheses 5 over 4 minus straight r over straight R close parentheses upto r = R, and ρ(r) = 0 for r > R, where r is the distance from the origin. The electric field at a distance r ( r < R) from the origin is given by

  • fraction numerator 4 space straight pi space straight rho subscript 0 straight r over denominator 3 straight epsilon subscript 0 end fraction space open parentheses 5 over 3 minus straight r over straight R close parentheses
  • fraction numerator begin display style space straight rho subscript 0 straight r end style over denominator begin display style 4 straight epsilon subscript 0 end style end fraction space open parentheses fraction numerator begin display style 5 end style over denominator begin display style 3 end style end fraction minus fraction numerator begin display style straight r end style over denominator begin display style straight R end style end fraction close parentheses
  • fraction numerator 4 space straight rho subscript 0 straight r over denominator 3 straight epsilon subscript 0 end fraction space open parentheses 5 over 3 minus straight r over straight R close parentheses
  • fraction numerator 4 space straight rho subscript 0 straight r over denominator 3 straight epsilon subscript 0 end fraction space open parentheses 5 over 3 minus straight r over straight R close parentheses

B.

fraction numerator begin display style space straight rho subscript 0 straight r end style over denominator begin display style 4 straight epsilon subscript 0 end style end fraction space open parentheses fraction numerator begin display style 5 end style over denominator begin display style 3 end style end fraction minus fraction numerator begin display style straight r end style over denominator begin display style straight R end style end fraction close parentheses

Apply shell theorem, the total charge upto distance r can be calculated as follows

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In a uniformly charged sphere of total charge Q and radius R, the electric field E is plotted as a function of distance from the centre. The graph which would correspond to the above will be


C.

straight E with rightwards arrow on top subscript inside space equals space open parentheses fraction numerator 1 over denominator 4 πε subscript straight o end fraction straight Q over straight R cubed close parentheses straight r with rightwards arrow on top
straight E with rightwards arrow on top subscript outside space equals space open parentheses fraction numerator 1 over denominator 4 πε subscript straight o end fraction straight Q over straight r cubed close parentheses straight r with rightwards arrow on top
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A thin spherical shell of radius R has charge Q spread uniformly over its surface. Which of the following graphs most closely represents the electric field E(r) produced by the shell in the range 0 ≤ r< ∞ , where r is the distance from the centre of the shell? 


A.

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