Two point charges of $20\,\mu C$ and $80\,\mu C$ are $10\,cm$ apart. Where will the electric field strength be zero on the line joining the charges from the $20\,\mu C$ charge? (in meters)

An infinite line charge produces a field of $9 \times 10^4 \text{ NC}^{-1}$ at a distance of $2 \text{ cm}$. Calculate the electric field produced at a distance of $3 \text{ cm}$.

Total charge $-Q$ is uniformly spread along the length of a ring of radius $R$. $A$ small test charge $+q$ of mass $m$ is kept at the centre of the ring and is given a gentle push along the axis of the ring.
$(a)$ Show that the particle executes a simple harmonic oscillation.
$(b)$ Obtain its time period.

Assertion: For a non-uniformly charged thin circular ring with net charge $0$,the electric field at any point on the axis of the ring is zero.
Reason: For a non-uniformly charged thin circular ring with net charge $0$,the electric potential at each point on the axis of the ring is zero.

Two charges $+5\,\mu C$ and $+10\,\mu C$ are placed $20\,cm$ apart. The net electric field at the midpoint between the two charges is

Explain electric field and its source as well as magnetic field and its source.