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

see full answer

Start JEE / NEET / Foundation preparation at rupees 99/day !!

21% of IItians & 23% of AIIMS delhi doctors are from Sri Chaitanya institute !!

An Intiative by Sri Chaitanya

$17.3 \times 10^{10}$

$17.3 \times 10^{12}$

$4.8 \times 10^{11}$

$1.73 \times 10^{10}$

answer is A.

(Unlock A.I Detailed Solution for FREE)

Ready to Test Your Skills?

Check your Performance Today with our Free Mock Test used by Toppers!

Take Free Test

Detailed Solution

$E l e c t r i c f o r c e i s b a l a n c e d b y g r a v i t a t i o n a l f o r c e . F_{E} = F_{G} \Rightarrow n e E = m g \Rightarrow n = \frac{m g}{e E} = \frac{ρ V \times g}{e E} = \frac{3000 \times \frac{4}{3} π {(2 \times 10^{- 3})}^{3} \times 9.81}{1.6 \times 10^{- 19} \times 3.55 \times 10^{5}} \Rightarrow n = 1.73 \times 10^{10}$