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, the focal length of the lens is:  


Correct option is



For real image, m is –ve.





The far-point of a short-sighted eye is 200 cm. The power of the lens is:


The near point of a short-sighted person is 10 cm and he desires to read a book 30 cm away from him. The power of the lens to be used by him is:


The distance between an object and the screen is 100 cm. A lens produces an image on the screen when placed at either of the positions 40 cm apart. The power of the lens is: 


A thin equiconvex lens has focal length 10 cm and refractive index 1.5. One of its faces is now silvered and for an object placed at a distance u in front of the lens, the image coincides with the object. The value of u is:


The plane face of a plano-convex lens of focal length 20 cm is silvered. What type of mirror will it become and of what focal length 


A convex lens of focal length 20 cm is cut into two equal parts so as to obtain two plano-convex lenses as shown in figure. The two parts are then put in contact as shown in figure. What is the focal length of the combination?



As shown in figure, a convergent lens is placed inside a cell filled with liquid. The lens has focal length +20cm when in air, and its material has refractive index 1.50. If the liquid has refractive index 1.60, the focal length of the system is: 



A plano-convex lens of f = 20 cm is silvered at plane surface. Now, f will be (μ = 1.5): 


The plane face of a plano-convex lens is silvered. If μ be the refractive index and R, the radius of curvature of curved surface, then the system will behave like a concave mirror of radius of curvature:


A ray of light suffers minimum deviation when incident on a 60o prism of refractive index  The angle of incidence is: