KEAM 2021 Physics and Chemistry Solved Paper

According to Coulomb's law, force between two charges at a certain distance d apart in air medium is given as,
F=‌

1

4πε0

‌

q1q2

d2

....(i)
where, ε0 is the permittivity of free space.
When these charges are kept in a dielectric medium, then force between them is given as
FD=‌

1

4πε0K

‌

q1q2

d2

.....(ii)
where, K is the dielectric constant.
Given, FD=‌

F

2

=‌

1

4πε0

‌

q1q2

2d2

=‌

1

4πε0K

‌

q1q2

d2

[from Eqs. (i) and (ii)]
⇒ K=2