A convex lens of focal length 10 cm is in contact with a concave lens. The focal length of the combination is numerically equal to that of the concave lens. The focal length of the concave lens is :
A diverging lens of focal length $-10cm$ is moving towards right with a velocity $5m/s$. An object, placed on principal axis is moving towards left with a velocity $3m/s$. The velocity of image at the instant when the lateral magnification produced is $1/2$ is: (All velocities are with respect to ground)
Lenses applied in achromatic combination having dispersive power in ratio of $5:3$ if focal of length of the concave lens is $15cm$, then focal length of the other lens will be:
Concave and convex lenses are placed torching each other. Ratio of magnitude of their power is $2:3$. The focal length of the system is $30\ cm$. Focal lengths of individual lenses are
When a telescope is adjusted for normal vision, the distance of the objective from the eye-piece is found to be 80 cm. The magnifying power of the telescope is 19. What are the focal lengths of the lenses ?
Two plano- concave lenses of glass of refractive index $1.5$ have radii of curvature of $20$ 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 $(4/3)$. Find the focal length of the system :
Which values for $K, L, M$ and $N$ will make the following paragraph true?
When an object of size $7\ cm$ is placed at the distance of $K$ in front of a $L$ of focal length $M,$ the image will be produced at the distance of $N$ in front of the mirror.
If two lenses of power + 1.5 D and +1.0 D are placed in contact, then the effective power of combination will be :
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 ?