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

A shortbar magnet placedin ahorizontal plane has Its axis aligned along the magnetic north-south .direction. Null points are found on the axis of themagnet at 14 cm from the centre of the magnet. The earth’s magnetic field at the place is 0.36 G and the angle of.dip is zero. What Is the total magnetic field on the normal bisector of the magnet at the same distance as the null”point (i.e, 14 cm) from the centre of the magnet? (At null points, field due to a magnet Is equal and opposite to the horizontal component of earth’s magnetic field)

+4e and +e are two charges separated by a distance 'a' m.Where should be a third charge 'q' be placed so that it is in equilibrium?