In the early 1900s, Robed Millikan used small charged droplets of oil. Suspended
ID: 1535254 • Letter: I
Question
In the early 1900s, Robed Millikan used small charged droplets of oil. Suspended in an electric field, to make the first quantitative measurements of the electron's charge. A 0.71- mu m-diameter droplet of oil, having a charge of is suspended in midair between two horizontal plates of a parallel-plate capacitor. The upward electric force on the droplet is exactly balanced by the downward force of gravity. The oil has a density of 860 kg/m^3, and the capacitor plates are 4.5 mm apart. What must the potential deference between the plates be to how the droplet in equilibrium?Explanation / Answer
d = 0.71 x10-6 m therefore r = 0.355 x 10-6 m
e = 1.602 x10-19 C
= 860 kg/m3
m = x vol.
m = 860 x (4/3)(pi r3)
m = 1.611608 x10-16 kg
g = 9.8 m/s2
For the drop to be stationary in mid air, the mass of the drop is balanced by the upward electric force .
mg = eE,
where E is the electric field between the the plates.
E = mg / e = 9858.77 N/C
The voltage between the plates = V = dE ,
where d is the distance between the plates.
V = 9858.77 x 4.5 x10-3
V = 44.36 Volts