Question

Do we have to include the signs (positive or negative)of the charges while solving problems?

Answer 1

Yes, we have to include the signs($+ve$ or $-ve$)of the charges while solving problems.

for example we have to calculate force between two positive charges $q_1$ and $q_2$. then force between them is:

$F=$ constant$\times (+q_1)\times (+q_2)=$some positive quantity.

and remember positive force is always repulsive.

while in other case suppose we have to calculate force between one negative charge q1 and one positive charge q2 then force is :

$F=$ constant$\times (-q_1)\times (+q_2)=$ some negative quantity.

and remember negative force is always attractive.

so, we have to include the signs(+ve or -ve)of the charges while solving problems to determine numerically whether a force is attractve or repulsive.