The distance between the plates of a parallel plate condenser is `8 mm` and `P.D. 120` volts. If a `6 mm` thick slab of dielectric constant `6` is introduced between its plates, then

Options

A. the charge on the condenser will be doubled
B. the charge on the condenser will be reduced to half
C. the `P.D.` across the condenser will be `320` volts
D. the `P.D.` across the condenser will be `45` volts

Answer

D

Explanation

If nothing is said, it is considered that battery is disconnected. Hence charge remain the same
Also `V_(air) = (sigma)/(epsilon_(0)) xx d` and `V_(medium) = (sigma)/(epsilon_(0)) (d - t + (t)/(K))`
`rArr (V_(m))/(V_(a)) = ((d - t + (t)/(k)))/(d) rArr (V_(m))/(120) = ((8 - 6 + (6)/(6)))/(8)`
`rArr V_(m) = 54 V`