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Electric Field for the circular path of positively charged particle

1 vote

Here is picture. Answers is A.


My attempt was that I thought if i were to place a positive test charge then it would go from top to bottom if there was a positive charge in the center it was avoiding and a positively charged particle at the top, but an electron at the bottom so it would avoid the positively charged particles and head for the electron thus the electric field would look like B and thats exactly how a positively charged particle would also do so.

But then the answer was A and i got thinking to how in circular motion there is centripetal force towards center, but honestly since this is electric fields i feel weird to correlate these and don't feel so correct.

asked Aug 30, 2019 in Physics Problems by aaryanb (120 points)

1 Answer

0 votes

Answer A is correct.

Imagine a fixed negatively charged particle at the focus of the electric field lines. The electric force is a central force. The free positively charged particle orbits in a circle around the fixed negative charge. There are other electric field lines apart from those shown, and only part of the circular path is shown.

A circular path is not the only possibility in a central force field. Parabolic and hyperbolic paths are also possible, as well as straight-line paths heading directly towards or away from the fixed charge. These paths look very nearly circular at the vertex, but further away they get straighter and straighter. The whole path is not circular.

Answer B would be possible if there is another force acting on the positively charged particle, like a friction or viscous force, which almost balances the electric force. The particle would then move at very slow speed, almost following the field lines but overshooting them by a very small amount. The overshoot can be made as small as you wish by making the electric and viscous forces more nearly equal. This kind of a curve is called a tractrix.

However, we are told nothing about any other forces so we have to assume that they do not exist.

answered Aug 31, 2019 by sammy gerbil (28,876 points)