An oil drop of 12 excess electrons is held stationary under a constant electric field of 2.55 x 10⁴ NC^–1 in Millikan’s oil drop experiment. The density of the oil is 1.26 g cm^–3. Estimate the radius of the drop. (g = 9.81 ms^–2: e = 1.60 x 10^–19 C).

Solution

Given,

$Electric field = 2.25 \times 10^{4} {NC}^{- 1} N umber of electrons = 12 D ensity of oil, ρ = 1.26 gm {cm}^{- 3} = 1.26 \times 10^{3} kg m^{- 3}$

Since, the droplet is stationary,
Weight of the droplet = force due to the electric field

$mg = Eq$

$∴$    $\frac{4}{3} {πr}^{3} ρ g = Ene$

$\Rightarrow$ $r^{3} = \frac{3 Ene}{4 π ρg}$
   $\Rightarrow r^{3} = \frac{3 \times 2.55 \times 10^{4} \times 12 \times 1.6 \times 10^{- 19}}{4 \times 3.14 \times 1.26 \times 10^{3} \times 9.81}$

$= 0.9 \times 10^{- 18}$

   $r = (0.9 \times 10^{- 18})^{1 / 3}$
$r = 9.81 \times 10^{- 7} m .$

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Electric Charges And Fields

An oil drop of 12 excess electrons is held stationary under a constant electric field of 2.55 x 10⁴ NC^–1 in Millikan’s oil drop experiment. The density of the oil is 1.26 g cm^–3. Estimate the radius of the drop. (g = 9.81 ms^–2: e = 1.60 x 10^–19 C).

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Figure shows tracks of three charged particles in a uniform electrostatic field. Give the signs of the three charges. Which particle has the highest charge to mass ratio?

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Electric Charges And Fields

An oil drop of 12 excess electrons is held stationary under a constant electric field of 2.55 x 104 NC–1 in Millikan’s oil drop experiment. The density of the oil is 1.26 g cm–3. Estimate the radius of the drop. (g = 9.81 ms–2 : e = 1.60 x 10–19 C).

Some More Questions From Electric Charges and Fields Chapter

Figure shows tracks of three charged particles in a uniform electrostatic field. Give the signs of the three charges. Which particle has the highest charge to mass ratio?

Mock Test Series

NCERT Sample Papers

Entrance Exams Preparation

An oil drop of 12 excess electrons is held stationary under a constant electric field of 2.55 x 10⁴ NC^–1 in Millikan’s oil drop experiment. The density of the oil is 1.26 g cm^–3. Estimate the radius of the drop. (g = 9.81 ms^–2: e = 1.60 x 10^–19 C).