Feedback on Class 12 (Physics-India) - Equipotential Surfaces

Dear All

Mr Ryan, Mr David and Mr. Mahesh (and of course Sal) . All these teachers are awesome. Following is the feedback on one of the lecture videos on Equipotential Surfaces

1. Mr. Mahesh explains things very clearly. I especially liked the way he explained on why in certain cases distance of a far away point from a DIPOLE (end)  can be taken to be equal to the distance of the point from the DIPOLE CENTRE and why in certain cases they cannot (Using Percentage error as the basis)

I have the following feedback on his lecture on Equipotential Surfaces:

It was hard for me to visualize how the surfaces change when two like or unlike point charges are brought close to each other. Here is a trick I found more helpful to visualize the same.

Imagine the equipotential surfaces  as  a fixed circular rubber band . Consider the case of two Like charges being brought close to each other. Since the field lines repel each other (equivalent to saying that the surfaces attract each other) , this can be imagined as someone placing their  left index finger at 0 deg of the left rubber band and right index finger at 180 deg of the right rubber band (Center of each band is the origin) and giving it a pull in opposite direction (left finger towards right and right finger towards left) . The resulting surfaces  are  egg shaped  and they will merge as Mr. Mahesh showed

Consider the case of two Unlike charges being brought close to each other. Since the field lines attract each other (equivalent to saying that the surfaces repel each other), this can be imagined as someone placing their  left index finger at 180 deg of the left rubber band and right index finger at 0 deg of the right rubber band (Center of each band is the origin) and giving it a pull in same direction (left finger towards left and right finger towards right) . The resulting shape is an egg shaped (at the other end compared to like charges)