Final answer:
The value of q that reduces the net electric force on each negatively charged particle to F/2 when placed midway between two -Q charges is Q/4. This is found using Coulomb's Law and considering the balancing of forces.
Step-by-step explanation:
The student is asking about the effect of inserting a charge +q between two charges of -Q. Initially, each -Q charge experiences a net electric force F. When the +q charge is placed midway, the force experienced by each -Q particle becomes F/2. To find the value of q that causes this reduction in force, we can use Coulomb's Law, which states that the electrostatic force F between two point charges is proportional to the product of their charges and inversely proportional to the square of the distance between them, F = k|q1*q2|/r2.
With the +q charge being midway between the -Q charges, it exerts an equal and opposite force on each -Q charge. The force on the -Q charge due to the other -Q charge is also present. Since the resultant force is halved, the force due to the +q charge must be equal to the original force F. Therefore, the magnitude of charge q must be Q/4, as it reduces the net force from F to F/2 on each -Q particle.