$12.$

A single charge $($Q $=3\mathrm{.}0\backslash$mu C$)$ is located at the origin of an axis system. A small test charge $($q $=1\mathrm{.}0$ pC$)$ is moved from x $=1\mathrm{.}0$ m to x $=-1\mathrm{.}0$ m$.$ Determine the amount of work done by the field for this displacement.

$0\mathrm{.}001$ J

$-0\mathrm{.}001$ J

$0$ J

More information is needed

$13.$

Describe the difference in shape for equipotential surfaces associated with a single negative charge and those associated with a single positive charge of twice the magnitude.

There is no difference

The positive charge equipotentials are not spherical

The negative charge equipotentials are not spherical