Question

A dielectric slab is inserted between the plates of a capacitor. The charge on the capacitor is Q and the magnitude of the induced charge on each surface of the dielectric is Q'.
(a) Q' may be large than Q.
(b) Q' must be larger than Q.
(c) Q' must be equal to Q.
(d) Q' must be smaller than Q.

Answer 1

(d) Q​' must be smaller than Q.

The relation between the induced charge Q' and the charge on the capacitor Q is given by
Q' = $Q\left(1-\frac{1}{K}\right)$
Here, K is the dielectric constant that is always greater than or equal to 1.
So, we can see that for K > 1, Q' will always be less than Q.