1.

An infinite sheet carrying a uniform surface charge density sigma1lies on the xy - plane . The work done to carry a charge q from the point vecA=a(hati-2hatj+6hatk)to the point vecB=a(hati-2hatj+6hatk)(where a is a constant with the dimension of length and epsilon_(0)is the permittivity of free space) is

Answer»

`(3sigmaaq)/(2epsilon_(0))`
`(2sigmaaq)/(epsilon_(0))`
`(5sigmaaq)/(2epsilon_(0))`
`(3sigmaaq)/(epsilon_(0))`

SOLUTION :Here`vecr_(A)=a(hati+2hatj+3hatk),vecr_(B)=a(hati-2hatj+6hatk)`
DISPLACEMENT VECTOR `vecr` from POINT A to B is `vecr=vecr_(B)-vecr_(A)`
`=a(hati-2hatj+6hatk)-a(hati+2hatj+3hatk)=a(-4hatj+3hatk)`
Electric field due to an infinite plane sheet of uniformsurface charge density `SIGMA` is
`vecE=(sigma)/(2epsilon_(0))hatn`where `hatn`is a unit vector normal to the plane.
Here ,`hatn=hatk`
`thereforevecE=(sigma)/(2epsilon_(0))hatk`
Work done in moving a charge q from A to B is
`W=vecF*vecr=qvecE*vecr ""(becausevecF=qvecE)`
`=q((sigma)/(2epsilon_(0))hatk)*a(-4hatj+3hatk)=(3sigmaaq)/(2epsilon_(0))`


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