Two charges placed in air repel each other by a force of `10^(-4)N`. When oil is introduced between the charges, then the force becomes `2.5 xx 10^(-5)N`
The dielectric constant of oil is

Options

A. 2.5
B. 0.25
C. 2
D. 4

Answer

D

Explanation

The force between two charges is given by
`F_(1)=(1)/(4pi epsilon_(0)).(q_(1)q_(2))/(R^(2))`
`rArr" "10^(-4)=(1)/(4pi epsilon_(0)).(q_(1)q_(2))/(R^(2))" …(i)"`
`"and "F_(2)=(1)/(4pi epsilon_(0)K).(q_(1)q_(2))/(R^(2))`
`rArr" "2.5xx10^(-5)=(1)/(4pi epsilon_(0)K).(q_(1)q_(2))/(R^(2))" ....(ii)"`
Now dividing Eq. (i) be Eq. (ii), we get
`(10^(-4))/(25xx10^(-5))=K or K=4.0`