 So solving these two you can get the alphabetic spectrum in school but don't get surprised also. This was last year's board exam was a point charge like this right now. A point charge but cute over here. It makes sense to define what is the potential energy per unit charge. So just like electric field which is force per unit charge, we are defining a potential energy per unit charge and that we call potential. The work done per unit charge or potential energy is the work done to move one unit of charge from infinity to the point of infinity to the point where you are finding the potential. By the infinity to that point. So everything boils down to the definition if you write like that otherwise you will not get mass. Now potential of a point charge just like electric field of a point charge is very simple. Which is what you know that potential energy between the two charges is k q1 q2 by r. So potential of a charge, let's say potential of a charge q1 at a distance r is k q1 by r. At a distance if charge is q the potential is eq potential surface. So if you move for example a point charge can you draw an eq potential surface? Around the point at the center. For a point charge has the same potential. All of you are clear right whatever is charged. Understand how potential or eq potential surface is placed with respect to electric potential. This should be equal to minus of q e dot delta r. So q delta v should be equal to minus of q e dot delta r. If we look at the potential. Now suppose the change is very very small. If change is very small is equal to minus of magnitude of e into magnitude of let's say dr into cos of angle between different direction of r into dr. From here you get e is equal to minus of dv by dr using this definition. Formula itself means that you have to partially differentiate. And the term to y totally let you feel it will be this i care plus that i care. Whichever is differentiating with respect to y you get relatively simple.