Advertisement Remove all ads

Show that the Equilibrium of the Test Charge is Necessarily Unstable - Physics

(a) Consider an arbitrary electrostatic field configuration. A small test charge is placed at a null point (i.e., where = 0) of the configuration. Show that the equilibrium of the test charge is necessarily unstable.

(b) Verify this result for the simple configuration of two charges of the same magnitude and sign placed a certain distance apart.

Advertisement Remove all ads

Solution

(a) Let the equilibrium of the test charge be stable. If a test charge is in equilibrium and displaced from its position in any direction, then it experiences a restoring force towards a null point, where the electric field is zero. All the field lines near the null point are directed inwards towards the null point. There is a net inward flux of electric field through a closed surface around the null point. According to Gauss’s law, the flux of electric field through a surface, which is not enclosing any charge, is zero. Hence, the equilibrium of the test charge can be stable.

(b) Two charges of same magnitude and same sign are placed at a certain distance. The mid-point of the joining line of the charges is the null point. When a test charged is displaced along the line, it experiences a restoring force. If it is displaced normal to the joining line, then the net force takes it away from the null point. Hence, the charge is unstable because stability of equilibrium requires restoring force in all directions.

Concept: Charging by Induction
  Is there an error in this question or solution?
Advertisement Remove all ads

APPEARS IN

NCERT Class 12 Physics Textbook
Chapter 1 Electric Charge and Fields
Q 32 | Page 50
Advertisement Remove all ads
Advertisement Remove all ads
Share
Notifications

View all notifications


      Forgot password?
View in app×