Use g = 9.8 m/s2. The classic Millikan oil drop experiment was the first to obtain an accurate measurement of the charge on an electron. In it, oil drops were suspended against gravity by a vertical electric field. Assume the oil drop to be 1.90 μm in radius and have a density of 900 kg/m3. (a) Find the weight of the drop. N (b) If the drop has a single excess electron, find the magnitude of the electric field strength needed to balance its weight. N/C
![You are still fascinated by the process of inkjet printing, as described in the opening storyline for this chapter [Check chapter Introduction of Chapter 22]. You convince your father to take you to his manufacturing facility to see the machines that print expiration dates on eggs. You strike up a conversation with the technician operating the machine. He tells you that the ink drops are created using a piezoelectric crystal, acoustic waves, and the Plateau-Rayleigh instability, which creates uniform drops of mass m = 1.25×10−8 g. While you don't understand the fancy words, you do recognize mass! The technician also tells you that the drops are charged to a controllable value of q and then projected vertically downward between parallel deflecting plates at a constant terminal speed of 18.5 m/s. The plates are ℓ = 2.25 cm long and have a uniform electric field of magnitude E = 6.35×104 N/C between them. Noting your interest in the process, the technician asks you, "If the position on the egg at which the drop is to be deposited requires that its deflection at the bottom end of the plates be 0.17 mm, what is the required charge on the drop?" You quickly get to work to find the answer.](https://www.doubtrix.com/uploads/editor/7923730467TGYRpgrIAs.png)