23. What is the magnitude of the electric eld between two large parallel plates 2.0 cm apart if a potential difference of 450 V is maintained between them? 27. An oil droplet of mass 2.6 X 1015 kg, suspended between two parallel plates 0.50 cm apart, remains stationary when the potential difference between the plates is 270 V. What is the charge on the oil droplet? How many excess or decit electrons does it have? 28. A metallic table tennis ball of mass 0.10 g has a charge of 5.0 X 10'6 C. What potential difference, across a large parallel plate apparatus of separation 25 cm, would be required to keep the ball stationary? 30. An electron is released from rest at the negative plate in a parallel plate apparatus kept under vacuum and maintained at a potential difference of 5.0 X 102 V. With what speed does the electron collide with the positive plate? 32. An electron with a speed of 5.0 X 106 m/s is injected into a parallel plate apparatus, in a vacuum, through a hole in the positive plate. The electron collides with the negative plate at 1.0 X 106 m/s. What is the potential difference between the plates