Tag: power of the lens

A convex lens of focal length 40 cm is in contact with a concave lens of focal length 25 cm. The power of he combination, is :

A far sighted person can see object beyond 71 cm clearly if separation between glasses and eye lens is 2 cm ,then find focal length of glass ?

If the magnitude of dispersive power of two lenses are $0.024$ and $0.036$. There focal length will be for abberation free combination.

In displacement method,magnification for two positions of the lens are 2 and 0.5 and the distance between the two position of the lens is 30 cm. if the focal length of lens is

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   :-