1) If an object is placed 20 cm from a convex lens and the image is formed 30 cm on the other side, what is the focal length? a) 10 cm b) 12 cm c) 15 cm d) 25 cm 2) An object is placed at 15 cm in front of a convex lens. If the focal length is 10 cm, where is the image formed? a) 30 cm b) 25 cm c) 20 cm d) 10 cm 3) For a convex lens, object distance = 12 cm, image distance = 12 cm. What is the focal length? a) 10 cm b) 11 cm c) 12 cm d) 6 cm 4) If a convex lens forms an image 60 cm away when the focal length is 20 cm away, what is the object distance? a) 10 cm b) 12 cm c) 20 cm d) 25 cm 5) The focal length of a lens is defined as.. a) Distance from the optical centre to the principal focus b) Distance from the object to the image c) Distance from the lens to the object d) Distance from the image to the eye 6) In a convex lens experiment, when a distant object (like the sun) is used, the image forms at.. a) Twice the focal length b) The focal plane of the lens c) The centre of curvature d) Beyond twice the focal length 7) Which formula is used to calculate focal length of a lens? a) f = u - v b) f = u + v c) f = uv d) 1/f = 1/𝑢+1/v 8) In the lens formula 1/f = 1/𝑢+1/v, u represents.. a) Image distance b) Object distance c) Focal distance d) Radius of curvature 9) A concave mirror produces a sharp image of the sun on a paper. The distance between mirror and image gives.. a) Radius of curvature b) Object distance c) Focal length d) Aperture size 10) For a concave mirror, the relation between radius of curvature (R) and focal length (f).. a) f = R b) f = 2R c) f = R2 d) f = R​/2

Demonstrate how to determine the focal length

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