Lenses Questions

In a certain camera, a combination of four similar thin convex lenses are arranged axially in contact. Then the power of the combination and the total magnification in comparison to the power ($p$) and magnification ($m$) for each lens will be, respectively:

A biconvex lens has a radius of curvature of magnitude $20\text{cm}$. Which one of the following options describes best the image formed of an object of height $2\text{cm}$ placed $30\text{cm}$ from the lens? (Assume refractive index $\mu =1.5$)

Two thin lenses of focal lengths $f_1$ and $f_2$ are in contact and coaxial. The power of the combination is:

A boy is trying to start a fire by focusing Sunlight on a piece of paper using an equiconvex lens of focal length $10\text{cm}$. The diameter of the Sun is $1.39\times 10^9\text{m}$ and its mean distance from the earth is $1.5\times 10^{11}\text{m}$. What is the diameter of the Sun's image on the paper?

A lens having focal length $f$ and aperture of diameter $d$ forms an image of intensity $I$. Aperture of diameter $d/2$ in central region of lens is covered by a black paper. Focal length of lens and intensity of image now will be respectively:

A converging beam of rays incident on a diverging lens intersects at $15\text{cm}$ on the opposite side. If the lens is removed, they meet $5\text{cm}$ closer. The focal length is:

When a biconvex lens of glass having refractive index $1.47$ is dipped in a liquid, it acts as a plane sheet of glass. This implies that the liquid must have refractive index:

A plano-convex lens (${\mu }_1$) fits exactly into a plano-concave lens (${\mu }_2$). Their plane surfaces are parallel. Focal length of the combination is:

Two identical glass (${\mu }_g=3/2$) equiconvex lenses of focal length $f$ each are kept in contact. The space between the two lenses is filled with water (${\mu }_w=4/3$). The focal length of the combination is: