(A) The electrostatic force between two charges $q_1$ and $q_2$ separated by a distance $r$ in a medium with dielectric constant $K$ is given by $F_m

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(A) The electrostatic force between two charges $q_1$ and $q_2$ separated by a distance $r$ in a medium with dielectric constant $K$ is given by $F_m = \frac{1}{4\pi\varepsilon_0 K} \frac{q_1 q_2}{r^2}$. In air,the dielectric constant $K_{air} \approx 1$,so the force is $F = \frac{1}{4\pi\varepsilon_0} \frac{q_1 q_2}{r^2}$. When the ions are placed in water,the new force $F'$ is given by $F' = \frac{1}{4\pi\varepsilon_0 K} \frac{q_1 q_2}{r^2}$. Comparing the two expressions,we get $F' = \frac{F}{K}$.

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

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$A$ force $F$ acts between sodium and chlorine ions of salt (sodium chloride) when placed $1 \ cm$ apart in air. The permittivity of air is $\varepsilon_0$ and the dielectric constant of water is $K$. When a piece of salt is placed in water,the electrical force acting between sodium and chlorine ions $1 \ cm$ apart is:

A
$\frac{F}{K}$
B
$\frac{FK}{\varepsilon_0}$
C
$\frac{F}{K\varepsilon_0}$
D
$\frac{F\varepsilon_0}{K}$

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Electric Charges and Fields

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Electrostatic Force and Coulombs Law

Two identical charged spheres are suspended by strings of equal lengths. The strings make an angle of $37^{\circ}$ with each other. When suspended in a liquid of density $0.7 \text{ g/cm}^3$,the angle remains the same. If the density of the material of the sphere is $1.4 \text{ g/cm}^3$,the dielectric constant of the liquid is . . . . . . $\left(\tan 37^{\circ} = \frac{3}{4}\right)$.

DifficultJEE MAIN 2024

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Three charges $+5 q, Q$ and $-2 q$ are kept along a straight line in the same order such that $+5 q$ and $-2 q$ charges are at a distance of $\frac{2 r}{3}$ and $\frac{r}{3}$ from the charge $Q$ respectively. If the net force on the charge $-2 q$ is zero,then $Q$ is

EasyAP EAMCET 2022

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Positive point charges are placed at the vertices of a star shape as shown in the figure. The direction of the electrostatic force on a negative point charge at the centre $O$ of the star is

DifficultKVPY 2017

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Two spherical conductors $B$ and $C$ having equal radii and carrying equal charges $Q$ repel each other with a force $F$ when kept apart at a distance $r$. $A$ third spherical conductor having the same radius as that of $B$ but uncharged is brought in contact with $B$,then brought in contact with $C$,and finally removed away from both. The new force of repulsion between $B$ and $C$ is

DifficultAIEEE 2004

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Two small balls,each having mass $m$ and charge $q$,are suspended from a common point by insulating strings of length $L$ as shown in the figure. Assuming $\theta$ is very small such that $\tan \theta \approx \sin \theta$,find the value of $x$ at equilibrium.

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Three charges $+5 q, Q$ and $-2 q$ are kept along a straight line in the same order such that $+5 q$ and $-2 q$ charges are at a distance of $\frac{2 r}{3}$ and $\frac{r}{3}$ from the charge $Q$ respectively. If the net force on the charge $-2 q$ is zero,then $Q$ is

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