Why do electric field lines emanate from positive charges?

Electric field lines emanate from positive charges because they represent the direction a positive test charge would move.

Electric field lines are a visual tool used in physics to represent the influence that electric charges have on their surroundings. They are drawn starting from positive charges and ending at negative charges, indicating the direction that a positive test charge would move if placed in the field. This is based on the fundamental principle that like charges repel and unlike charges attract.

The concept of electric field lines was introduced by Michael Faraday. He used these lines to describe how an electric field behaves. The lines are drawn such that the tangent at any point on the line gives the direction of the electric field at that point. The density of these lines in a region represents the magnitude of the electric field: the denser the lines, the stronger the field.

The reason why electric field lines emanate from positive charges is due to the nature of electric forces. Electric forces are vector quantities, meaning they have both magnitude and direction. The direction of the electric force on a positive test charge is always away from other positive charges and towards negative charges. Therefore, when we draw electric field lines, we start them at positive charges (to represent the force pushing away) and end them at negative charges (to represent the force pulling towards).

This convention is a reflection of the fundamental properties of electric charges. It's important to note that the choice of a positive test charge is a convention. We could, in theory, choose a negative test charge, but then the field lines would be in the opposite direction. However, the positive test charge convention is universally accepted and used because it simplifies the understanding and calculation of electric fields.

In conclusion, electric field lines emanate from positive charges because they are a visual representation of the direction and magnitude of the electric field, which is determined by the fundamental properties of electric charges.