Question

it is required to hold 4 equal point charges +q in equilibrium at the corners of a square. Find the point charge that will do this if placed at the centre ​

Answer 1

U just need to place a point Charge of +q charge at the center so that all the +q charges present at the corners of the square repel it with equal force and all these forces will cancel out each other as the are equal and opposite

The if -q point charge is placed then also the system will be in equilibrium

But in physics point Charges.are always considered to be positive

Pls Refer the attachment

I hope this helps( ╹▽╹ )