The figure shown four situations in which charges as indicated `(q gt 0)` are fixed on an axis. How many situations is there a point to the left of the charges where an electron would be ib equilibrium?

Answer

2

Explanation

For (1)
Let the electron be held at a distance x from `+q` charge.
For equilibrium `(q(-e))/(4pi in_(0) x^(2))+((-e)(-4q))/(4pi in_(0)(x+d)^(2))=0`
We can find value of x for which `F_("net")=0` which means that electron will be in equilibrium.
For (2):
For equilibrium `((-e)(-q))/(4pi in_(0)x^(2))+((-e)4q)/(4pi in_(0)(x+d)^(2))=0`
We can find value of x for which `F_("net")=0` which means that electron will be in equilibrium. In case (3) and (4) the electron will not remain at rest, since it experiences a net non-zero force.
OR
Equilibrium is always found near the smaller charge