Question: Two charges approach the origin at constant velocity from opposite directions along the axis. They collide and stick together, forming a neutral particle at rest. Sketch the electric field before and shortly after the collision (remember that electromagnetic "news" travels at the speed of light). How would you interpret the field after the collision, physically?

The magnitude of two charges approaching the origin is-q and +q .

The two charges are approaching the origin at constant velocity from opposite directions along the x axis.

Consider a particle having certain amount of charge moves through the space then an electric field around the charge is generated. The amount of charge on the particle and its radius affects the electric field.

The direction of the electric field for a positive point charge is always radially outwards while for a negative point charge is radially inwards.

According to the question, when two charges and are approaching the origin at a constant velocity then the electric field lines for both charges emanate from the present position of particle. The direction of the electric field lines for the negative charge is converging inwards the center of the charge while the direction of the electric field lines for the positive charge is diverging outwards from the center of the charge.

Hence, theelectric field before the collision of the charge is represented.

Conisder two charges -q and +q approaching the origin at a constant velocity collide each other then, shortly after the collision both charges stick together and move with the same velocity.

Both charges are traveling with the constant velocity equal to the speed of light.

Then the radius of the combined charge formed after a short time of the collision can be given as,

The direction of the electric field lines inside the spherical charge is entering from the negative side of the charge and exiting from the positive side of the charge. It means that a dense cluster of tangentially-directed field lines is produced in the spherical shell of the charge after the collision.

Inside the spherical charge the value of the electric field produced is zeroafter the collision of two equal and opposite charges.

Hence, the electric field just after the collision of the charge is represented.