Concentric equipotential surfaces due to a charged body . . .

Question : Concentric equipotential surfaces due to a charged body placed at the centre are shown. Identify the polarity of charge and draw the electric field lines due to it. Justify your answer. 

Doubt by Riddhi 

Solution : 

We know, 

Electric Potential due to an isolated charge particle q is given by 

V=kq/r

If q is +ve then as r increases the value of electric potential will decrease. 

If q is -ve then as r increases the value of electric potential will increases. 

As shown in our question as distance r increases from the charge the magnitude of electric potential increase, it means the polarity of charge q is -ve. 

Electric field lines due to a charge -q will be radially inward i.e. directing from higher potential to lower potential because we know that the electric potential always decreases in the direction of electric field as shown below.