In the early 1900s, Robert Millikan used small charged drop lets of oil, suspend

Question

In the early 1900s, Robert Millikan used small charged drop lets of oil, suspended in an electric field, to make the first quantitative measurements of the electron's charge. A 0.7 0-^m-diameter droplet of oil, having a charge of +e, 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/m3, and the capacitor plates are 5.0 mm apart. What must the potential difference between the plates be to hold the droplet in equilibrium?

Explanation / Answer

Ans: If E be the electric field, q be the charge of the droplet., and m be the mass of the droplet then at equilibrium.

qE=m*g , where g =9.8 m/sec^2

Here, q=+e ; mass= volume*density =(4/3)*pi*(0.7x10-6/2)3 *860 kg =4.14x 10-10 kg.

Now E=potential/distence =V/d ; here d= 5 mm= 0.005 m

So Vpotential = mg*d/e =1.35x 108 V

Related Questions

Navigate

• Browse (All)
• Browse I
• Subjects

---