A object is placed 30 cm from a convex lens. A real image is formed 20 cm from the lens . Find the focal length of the lens.

A convex mirror and convex lens of radius of curvature 20 cm are placed on same axis with 30 cm separation. A point-like object is placed at 20 cm from convex lens and its image by this combination is obtained at object. What will be focal length of convex lens ?

A screen is placed 90cm from an object. The image of the object on the screen is formed by a convex lens at two different locations separated by 20cm. Determine the focal length of the lens.

Two point objects are placed on principal axis of a thin converging lens. One is 20cm from the lens and other is on the other side of lens at a distance of 40 cm from the lens. The images of both objects coincide. The magnitude of focal length of lens is :-

The redius of curvature of the convex face of a plano-convex lens is 12cm and its refractive index is 1.5. a. Find the focal length of this lens. The plane surface of the lens is now silvered. b. At what distance form the lans will parallel rays incident on the convex face converge? c. Sketch the ray diagram to locate the image, when a point object is places on the axis 20cm from the lens. d. Calculate the image distance when the object is placed as in (c).

Shown an object and its image formed by a thin lens. Then the nature and focal length of lens is

A lens placed between a candle and a fixed screen forms a real triply magnified image of the candle on the screen. When the lens is moved away form the candle by 0.8m without changing the position of the candle, a real image one-third the size of the candle is formed on the screen. Determine the focal length of the lens.

Lens of power +2.0 D is a convex lens.

A point object is kept at a distance of 2 m from a parabolic reflecting surface y^(2) = 2x . An equiconvex lens is kept at a distance of 1.80 m from the parabolic surface. The focal length of the lens is 20 cm . Find the position from origin of the image in cm, after reflection from the surface.

A convex lens is placed between an object and a screen which are at a fixed distance apart for one position of the lens. The magnification of the image obtained on the screen is m_(1) . When the lens is moved by a distance d the magnification of the image obtained on the same screen m_(2) , Find the focal length of the lens.

A point object is placed on the axis in front of a convex lens of focal length 30 cm. The distance of the object from the lens is 45 cm. If the lens is moved away from object by 1 mm and also the object is moved apart from the line joining the object and optical centre by 1 mm the displacement of the image has magnitude-