Ela posted the question: “ Sir, we know that a negatively charged particle has electric field lines coming radially towards it but what is the origin of these lines?”
The electric field lines are just a diagrammatic representation of electric field. The electric field is real but the electric field lines are imaginary. The direction of electric field is also given a conventional definition as “the direction in which a free positive test charge moves in a field.”
Positive and negative are just two kinds of charge. The name “positive” and “negative” are just an arbitrary choice. When a charge is present in space it modifies its surrounding such that another charge kept in its vicinity will experience a force.
If a positive test charge is kept near a negative charge, it will move towards the negative charge. That is why the direction of electric field lines are towards it. Theoretically, electric field lines extend to infinity. (Remember, infinity is also a relative concept. For an amoeba, an ant is infinitely large. For an ant, an elephant is infinitely large and so on.) Just for the sake of it, we can imagine that the lines of force are coming from positive charge(s) at infinity