Final answer:
The electric field at the midpoint between two point charges of equal magnitude but opposite charges is zero, due to the principle of superposition.
Step-by-step explanation:
The student asks about the electric field at the midpoint between two point charges A and B having charges q and −q respectively, which are 2L apart. To find the electric field at the midpoint, we can use the principle of superposition of electric fields, which states that the total electric field due to multiple point charges is the vector sum of the electric fields due to each charge taken individually.
For charges of equal magnitude but opposite signs, the electric fields at the midpoint due to each charge will be equal in magnitude but opposite in direction. Therefore, they will cancel each other out. As a result, the total electric electric field at the midpoint between A and B is zero.