Two charges of equal magnitude q are placed in air at a distance 2 a apart and third charge -2q is placed at mid – point. The potential energy of a system is? ( ԑo = permittivity of free space ) . (MHT-CET ~ 2014)

Two charges of equal magnitude q are placed in air at a distance 2 a apart and third charge -2q is placed at mid – point. The potential energy of a system is? ( ԑ_o = permittivity of free space ) . (MHT-CET ~ 2014)

a ] - q ² / ( 8 π ε _o a )                        b] - 3 q ² / ( 8 π ε _o a )                     

c] – 5 q ² / ( 8 π ε _o a )                     d] - 7 q ² / ( 8 π ε _o a )

Two concentric sphere kept in air have radii R & r . they have similar change and equal charge density σ. The electric potential at their common centre is? ( MHT - CET ~ 2014 )

Two concentric sphere kept in air have radii R & r . they have similar change and equal charge density σ. The electric potential at their common centre is? ( MHT - CET ~ 2014 )

a ]  σ ( R + r ) / ε _o            b ] σ ( R – r ) / ε _o

c ] σ ( R + r ) / 2 ε _o               d ] σ ( R + r ) / 4 ε _o