A converging beam of light is incident on a concave lens. The beam converges behind the lens at $15 \mathrm{cm}$ from its centre, in the absence of the lens. Select the correct alternative

When the space between two glass lenses in combination shown in figure is filled with water, then

. A point object is placed $30 \mathrm{cm}$ in front of an equiconvex lens of radius of curvature $15 \mathrm{cm}$ and made of glass of refractive index $\frac{3}{2}.$ On placing a convex mirror of radius of curvature $15 \mathrm{cm}$ behind the lens on image side as shown in figure, the final image is found to coincide with the object. The possible distance $\mathrm{x}$ between convex lens and convex mirror is

A converging lens is used to form an image on a screen. When the upper half of the lens is covered by an opaque screen

A point object $O$ is placed at a distance of $30 \mathrm{cm}$ from a convex lens of focal length $20 \mathrm{cm},$ cut into two halves each of which is displaced by $5\times {10}^{-2} \mathrm{cm}$ as shown. Choose the correct option(s).