Question

In the figure,if net force on Q is zero then value of Q/q is

Answer 1

net force on Q is zero , it means Q and q are in opposite nature .
Let Q is positive nature and q is negative nature
Then, force between Q and Q will be repulsion,
And force between Q and q will be attraction,

Now, net force act on Q =net force act by q - net force act by Q on Q = 0
net force act by q on Q = net force act by Q on Q
$\sqrt{[\frac{KqQ}{r^2}]^2+[\frac{KqQ}{r^2}]^2}=\frac{KQQ}{(\sqrt{2}r)^2}\\\\\sqrt{2}\frac{KqQ}{r^2}=\frac{KQQ}{r^2}\\\\2\sqrt{2}qQ=Q.Q\\\\2\sqrt{2}=\frac{Q}{q}$

Hence, Q/q = 2√2 is the right answer