Reference no: EM131552666

Question: A droplet 10 μm in radius will fall in air at a steady velocity of 1.1cm/s because its weight mg (m is its mass, g is the acceleration due to Earth's gravity) is balanced by the viscous force 6πηav (η is the viscosity of air, 18.2 μPas; a is the radius of the droplet; and v is the velocity of fall).

a. Use these data to find the radius of a droplet that falls with a velocity of 8.59 ×10^-4 m/s.

b. When an electric field of 317.5kV/m is turned on, the droplet in (a) is observed to rise at a steady speed of 2.41 × 10^-4 m/s.

c. Show that the upward electrical force on the droplet is 1.28 times the downward gravitational force mg.

d. To within a couple of electrons, how many excess electrons are there on this droplet?

e. What important conclusions do we draw from Millikan's measurements?