How do you correct monochromatic aberration?

A deviation of $2°$ is produced in the yellow ray when prism of crown and flint glass are achromatically combined. Taking dispersive powers of crown and flint glass are $0.02$ and $0.03$ respectively and refractive index for yellow light for these glasses are $1.5$ and $1.6$ respectively. The refracting angles for crown glass prism will be ________$°$ (in degree)

(Round off to the Nearest Integer)

A convex lens $L$ and plane mirror $M$ are arranged as shown in figure. Position of the object pin $O$ is adjusted in such a way that the inverted image $I$ formed by the lens mirror combinations, coincides with the object pin $O$. Explain how and when this happens.

A combination consisting of a concave lens in contact of a convex lens of focal length $25 \mathrm{cm}$ produces a real image at a distance of $80 \mathrm{cm}$ when an object is placed at a distance of $40 \mathrm{cm}$ from the combination. Find the focal length and power of the concave lens.

Parallel rays of sun fall upon a concave lens of $10 \mathrm{cm}$ focal length. At a distance of $20 \mathrm{cm}$ from this lens, a convex lens of $15 \mathrm{cm}$ focal length is placed. Where should the screen be placed to get the image of the sun?

For next Two questions

A hollow cylindrical beam of white light is incident on a converging lens in air. Axis of the beam coincides with the principle axis of the lens. A screen is placed behind the lens.

If ${\mathit{\text{f}}}_{\text{v}}$ is focal length for violet light and ${\mathit{\text{f}}}_{\text{R}}$ is focal length for red light, then

In producing a pure spectrum, the incident light is passed through a narrow slit placed in the focal plane of an achromatic lens because a narrow slit

Lenses of powers $+3 \mathrm{D}$ and $-5 \mathrm{D}$ are combined to form a compound lens. An object is placed at a distance of $50 \mathrm{cm}$ from this lens. Calculate the position of its image.

Reason: The refractive index of material of lens is different for different wavelengths of light.