The principle mentioned in the question refers to the ability of a Van de Graff generator to accumulate large amounts of charge on a conducting sphere. This device uses the concept of continuous charge transfer and electrostatic induction to accumulate and store high-voltage electric charge. Thus, the principle described corresponds to the Van de Graff generator, which operates by continuously transferring charge onto a large conducting sphere.
Final Answer: Van de Graff generator
Two charges, \( q_1 = +3 \, \mu C \) and \( q_2 = -4 \, \mu C \), are placed 20 cm apart. Calculate the force between the charges.