Question 389: Electrostatics & Capacitance

Question

An oil drop of radius 2 mm with a density 3g cm
$$-$$3
is held stationary under a constant electric field 3.55 $$	imes$$ 10
5
V m
$$-$$1
in the Millikan's oil drop experiment. What is the number of excess electrons that the oil drop will possess? (consider g = 9.81 m/s
2
)

Accepted Answer

F
e
= qE = (ne)E
F
e
= mg
(ne)E = mg
$$n = {{mg} \over {eE}} = {{ho {4 \over 3}\pi {R^3} 	imes g} \over {eE}}$$
$$n = {{3000 	imes {4 \over 3} 	imes 3.14 	imes 8 	imes {{10}^{ - 9}} 	imes 9.8} \over {1.6 	imes {{10}^{ - 19}} 	imes 3.55 	imes {{10}^5}}}$$
$$n = {{984704 	imes {{10}^5}} \over {5.68}} = 1.73 	imes {10^{10}}$$
$$n = 1.73 	imes {10^{10}}$$

Answer

48.8 $$	imes$$ 10
11

Answer

1.73 $$	imes$$ 10
10

Answer

17.3 $$	imes$$ 10
10

Answer

1.73 $$	imes$$ 10
12

Electrostatics & Capacitance

An oil drop of radius 2 mm with a density 3g cm $-3 is held stationary under a constant electric field 3.55 \times 10 5 V m -$1 in the Millikan's oil drop experiment. What is the number of excess electrons that the oil drop will possess? (consider g = 9.81 m/s 2 )

Choose the correct answer: