The plates of a parallel plate capacitor are charge upto 100 V. A 2 mm thick insulator sheet is inserted between the plates. Then to maintain the capacitor plates is increased by 1.6 mm, dielectric constant of the insulator is

Options

A. `5`
B. `1.25`
C. `4`
D. `2.5`

Answer

A

Explanation

As battery is disconnected, so charge will remain the same. It is given that final potential is the same. So final capacitance should be equal to initial capacitance, i.e.
`(epsilon_(0)A)/d=(epsilon_(0)A)/((1.6+d)-t(1-1//K))`
or `K = 5`.