Tag: ray optics and optical instruments

The refractive index of the material of a double convex lens is $1.5$ and its focal lengths in $5cm$. If the radii of curvature are equal, the value of the radius of curvature is

In a plano convex lens, the radius of curvature of the convex iens is 10 cm, if the plane side is polished , then the focal length is (Refractive index=1.5)

When a thin convex lens of focal length $10cm$ is kept in contact with a diverging lens, the power of the combination is found to be $-10D$. The focal length of the other lens is

A lens made from a material of absolute refractive index $\mathrm { n } _ { 1 }$  and it is placed in a medium of absolute refractive index $\mathrm { n } _ { 2 }$   The focal length of the lens is related to $\mathrm { n } _ { 1 } \text { and } \mathrm { n } _ { 2 }$ as:

Two lenses of power 12 and -2 dioptre are placed in contact. The focal length of the combination is 

Two thin convex lenses of focal length 10 cm  and 15 cm are separated by a distance of 10 cm. The  focal length of combination is   :-

A convex lens of focal length 10 cm is being placed in contact with a concave lens of focal length 20 cm. The focal length of the combination is.

A point object is placed at a distance of $15 cm$ from a convex lens. The image is formed on the other side at a distance of $30cm$ from the lens. When a concave lens is placed in contact with the convex lens, the image shifts away further by $30 cm$. Calculate the focal lengths of the concave and convex lenses.

Two plano-convex lenses of glass of refractive index $1.5$ have radii of curvature $20\ cm$ and $30\ cm$. They are placed in contact with curved surfaces towards each other and the space between them is filled with a liquid of refractive index $4/3$. The focal length of the combination is

An achromatic combination of a concave and convex lenses  has power 5D. If the power of convex lens is 4 D then the magnitue of focal length of concave lens is