Lens

A convex lens of power $4\mathrm{D}$ and a concave lens of power $-3\mathrm{D}$ are placed in contact, the equivalent power of combination is

Power of combined lenses of focal lengths $20 \mathrm{cm}$ and $25 \mathrm{cm}$ respectively:

A convex lens of focal length $40 \mathrm{cm}$ is kept in contact with a concave lens of focal length $-25 \mathrm{cm}.$ The power of the combination is

In the figure $\left(\mathrm{i}\right)$ a thin lens of focal length $10 \mathrm{cm}$ is shown. The lens is cut into two equal parts and arranged as shown in the figure $\left(\mathrm{ii}\right).$ An object $AB$ of height $1 \mathrm{cm}$ is placed at a distance of $7.5 \mathrm{cm}$ then, height of the final image will be

A plano-convex thin lens of focal length $10 \mathrm{cm}$ is silvered at its plane face. The distance $d$ at which an object must be placed in order to get its image on itself is:

Two thin lenses of power $+5 \mathrm{D}$ and $-2 \mathrm{D}$ are placed in contact with each other. The focal length of the combination will be a

An object is placed at a distance of$12 \mathrm{cm}$ to the left of a converging lens of focal length $8 \mathrm{cm}.$ Another converging lens of focal length $6 \mathrm{cm}$ is placed at a distance of $30 \mathrm{cm}$ from the object to the right of the first lens. The second lens will produce-

In order to obtain image of a bulb on a wall of at a distance $d$ from the wall, a convex lens is placed between the bulb and the wall. Focal length of lens will be

A student measures the focal length of a convex lens by putting an object pin at a distance $u$ from the lens and measuring the distance $v$ of the image pin. The graph between $\text{'}u\text{'}$and$\text{'}v\text{'}$ plotted by the student should look like -

An equiconvex lens is cut into two halves along $\left(\mathrm{i}\right)$ $XOX\text{'}$ and $\left(\mathrm{ii}\right)$ $YOY\text{'}$ as shown in the figure. Let $f, f^{\text{'}}, f^{\text{'}\text{'}}$ be the focal lengths of the complete lens, first half cut along $XO{X}^{\text{'}}$ and second half cut along $YO{Y}^{\text{'}}$ respectively.

Choose the correct statement from the following:

A thin convex lens of refractive index $1.5$ is placed in a liquid with refractive index $2.0.$ If the power of the lens in air is $10 \mathrm{D}$ then, its power in the liquid will be

A point object is placed at the focus of a double concave lens. The image is formed

A convex lens makes a real image of height $4 \mathrm{cm}$ on a screen. When the lens is shifted to a new position without disturbing the object or the screen, a real image of height$16 \mathrm{cm}$ is obtained on the screen. The length (height) of the object is :

A thin symmetrical double convex lens of power $P$ is cut into three parts as shown in the figure below. Power of $A$ is:

The correct conclusion that can be drawn from these figures is

A lens made of glass of refractive index $1.5$ has a focal length of $10 \mathrm{cm}$ in air and $50 \mathrm{cm}$ when completely immersed in a liquid. Then the refractive index of the liquid is-

In the figure, an air lens of radii of curvature $10 \mathrm{cm}\left(R_1=R_2=10 \mathrm{cm}\right)$ is cut in a cylinder of glass $(\mu =1.5).$ The focal length and the nature of the lens is

A convex lens forms a real image of a point object placed on its principal axis. If the upper half of the lens is painted black, the image will

The radius of curvature of the convex surface of a thin plano-convex lens is $15 \mathrm{cm}$ and refractive index is $1.6$. The power of the lens is ?

A divergent lens will produce