(D) For the drop to remain stationary,the upward electric force must balance the downward gravitational force.$qE = mg$Given:$E = 100 \ V m^{-1}$$m =

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(D) For the drop to remain stationary,the upward electric force must balance the downward gravitational force.$qE = mg$Given:$E = 100 \ V m^{-1}$$m = 1.6 \times 10^{-3} \ g = 1.6 \times 10^{-6} \ kg$$g \approx 10 \ m s^{-2}$$q = \frac{mg}{E} = \frac{1.6 \times 10^{-6} \times 10}{100} = 1.6 \times 10^{-7} \ C$The number of electrons $n$ is given by $n = \frac{q}{e}$,where $e = 1.6 \times 10^{-19} \ C$.$n = \frac{1.6 \times 10^{-7}}{1.6 \times 10^{-19}} = 10^{12}$.

Class 12 Physics Electric Charges and Fields Electrostatic Force and Coulombs Law

Medium

$A$ negatively charged oil drop is prevented from falling under gravity by applying a vertical electric field of $100 \ V m^{-1}$. If the mass of the drop is $1.6 \times 10^{-3} \ g$,the number of electrons contained in the drop is:

A
$10^{18}$
B
$10^{15}$
C
$10^6$
D
$10^{12}$

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Class 12

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Chapter

Electric Charges and Fields

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Electrostatic Force and Coulombs Law

Write the limitations of Coulomb's law.

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$A$ charge of $0.8 \text{ C}$ is divided into two charges $Q_{1}$ and $Q_{2}$. These are kept at a separation of $30 \text{ cm}$. The force on $Q_{1}$ is maximum when

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Electrostatic force between two identical charges placed in vacuum at a distance of $r$ is $F$. $A$ slab of width $\frac{r}{5}$ and dielectric constant $9$ is inserted between these two charges. The new force between the charges is:

DifficultAP EAMCET 2022

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When air is replaced by a dielectric medium of constant $k$,the maximum force of attraction between two charges separated by a distance $r$:

EasyAIPMT 1999

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The force between two point charges $A$ and $B$ is $F$. If $75\%$ of the charge on $A$ is transferred to $B$,then the new force between $A$ and $B$ is:

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$A$ negatively charged oil drop is prevented from falling under gravity by applying a vertical electric field of $100 \ V m^{-1}$. If the mass of the drop is $1.6 \times 10^{-3} \ g$,the number of electrons contained in the drop is:

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