Final answer:
Spray transfer in an electrostatic paint sprayer requires a minimum high voltage to charge paint droplets and control of environmental conditions to ensure efficient coating of the target surface.
Step-by-step explanation:
Spray transfer requires at least a minimum voltage and control of environmental conditions. The question mentions an electrostatic paint sprayer with a 0.200-m-diameter metal sphere at a potential of 25.0 kV that repels paint droplets onto a grounded object. To achieve effective spray transfer, certain requirements must be met to ensure the droplets are properly charged and can be directed towards the target surface.
In electrostatic spray systems, it is important that the paint droplets have an opposite charge to the target object, promoting attraction. The high voltage potential of the paint sprayer aids in charging the droplets which are then attracted to the grounded object due to the potential difference. Furthermore, environmental conditions such as humidity and temperature can affect the spray transfer, and hence, those conditions should also be controlled to minimize disruptions caused by airborne contaminants.