IIT JEE , AIEEE Forum - Physics , Electricity

Ank999

Q1 A metal sphere of radius R is charged to a potential V.

(a) Find the electrostatic energy stored in the electric field within a concentric sphere of radius 2R.

(b) Show that the electrostatic field energy stored outside the sphere of radius 2R equals that stored within it.

Q2 A large conducting plane has a surface charge density 1.0 * 10^-4C/m²

Find the electrostatic energy stored in a cubical volume of edge 1.0 cm in front of the plane.

edison

use the concept that energy density i.e energy stored per unit volume in electric field is given by

= (1/2) x permittivity x (Electric field intensity)^2

splashprabhu

assume a gaussian spherical surface of radius r , suppose charge inside is Q

E = Q / (4

r²)

firstly, V =- _{[ 0]}

^{[ R]} E.dr

V = Q/4

R

Q= 4

RV....{i}

V = - _{[R ]}

^{[ 2R]} E.dr...

V = Q / (8

R) = V/2 .........{ii}

U = (1/2)C(

V)² = Q

V/2 =

RV²........frm i & ii & C = Q/

V

now since V = V_R - V(infinity)

V = V_R-V_2R

V_2R - V(infinity) =V -

V = V/2

so we get d same potential diff...n same charge so...same electrostatic energy

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