Question
Suppose one of the 12 q's is removed. What is the force on Q?
Answer
Due to the removal of one q, there is no opposite balancing force existing anymore to nullify the repulsive force of the q sitting at exact opposite corner of vacant site. Rest of the pairs are still in their position, balancing their forces. As a result, the test charge Q will only feel the coulomb force due that single q charge.
If $F_Q$ is the force experienced by the test charge Q, then
Suppose one of the 12 q's is removed. What is the force on Q?
Answer
Due to the removal of one q, there is no opposite balancing force existing anymore to nullify the repulsive force of the q sitting at exact opposite corner of vacant site. Rest of the pairs are still in their position, balancing their forces. As a result, the test charge Q will only feel the coulomb force due that single q charge.If $F_Q$ is the force experienced by the test charge Q, then
$F_Q = Qq/4\pi\epsilon_or^2$
Where r is the distance between charge Q and q.