A point object is moving at a constant speed of 1 ms$$^{-1}$$ along the principal axis of a convex lens of focal length 10 cm. The speed of the image is also 1 ms$$^{-1}$$, when the object is at ............. cm from the optical centre of the lens.

The power of a equi-concave lens is $$-4.5 \mathrm{D}$$ and is made of a material of refractive index 1.6, the radii of curvature of the lens is

A ray of light passes through an equilateral glass prism in such a manner that the angle of incidence is equal to the angle of emergence and each of these angles is equal to $$\frac{3}{4}$$ of the angle of the prism. The angle of deviation is

A convex lens of focal length $$f$$ is placed somewhere in between an object and a screen. The distance between the object and the screen is $$x$$. If the numerical value of the magnification produced by the lens is $$m$$, then the focal length of the lens is