Electric Charge...

Two point charges $$q$$ and $$-4q$$ are placed at points $$A$$ and $$B$$ respectively, at a distance $$d$$ apart as shown in the figure. The null point (the point where electric field is zero) is :

A cubical region of side $$'a'$$ has its centre at the origin. It encloses three fixed point charges, $$-q$$ at $$(0, -a/4, 0), +3q$$ at $$(0, 0, 0)$$ and $$-q$$ at $$(0, +a/4, 0)$$. Choose the incorrect option

Two equal and opposite point charges are kept in a box. A vacuum is created in the box by evacuating the air inside the box. Then the electrostatic force between the two charges will:

A particle of charges $$q_{0}$$ is moved around a charges $$+q$$ along the semicircle path of radius $$r$$ from $$A$$ to $$B$$ (see figure). The work done by the Coulomb force is

A charged particle $$q$$ is placed at the centre $$O$$ of cube of side $$L (ABCDEFGH)$$. Another same charge $$q$$ is placed at a distance $$L$$ from $$O$$, then the electric flux through $$ABCD$$ is

Two charges $$q_{1}$$ and $$q_{2}$$ are moving with velocity $$\vec {V_{1}}$$ and $$\vec {V_{2}}$$ parallel to each other in vacuum as shown. Then,

Two point charges $$+q$$ and $$-4q$$ are placed at $$(-a, 0)$$ and $$(+a, 0)$$. Take electric field intensity to be positive if it is along positive $$x-$$direction. The variation of the electric field intensity as one moves along the $$x-$$axis is: 

To construct an air filled capacitor which can store $$ 12 \mu C $$ of charge, What can be the minimum plate area of the capacitor? (Dielectric strength of air is $$3\times 10^6 V/m$$ )

Three charge $$+4q,\ Q$$ and $$q$$ are placed in a straight line of length $$\ell$$ at points distance $$0,\ \ell/2$$ and $$\ell$$ respectively. What should be the value of $$Q$$ in order to make the net force on $$q$$ to be zero?

Consider a hemispherical surface of radius $$r$$, a positive point charge $$q$$ is kept at the centre of hemisphere. The electric flux through this hemisphere is :