If the focal length of a camera lens is 20cm, the distance from the film at which the lens must be set to produce a sharp image of an object 100cm away is

Answer Details

To produce a sharp image of an object, the light rays coming from the object must converge at a single point on the camera film. The distance between the lens and the film determines where the image will be in focus. In this case, the focal length of the camera lens is given as 20cm, and the distance from the object to the lens (object distance) is 100cm. To find the distance from the film to the lens (image distance) that will produce a sharp image, we can use the formula: 1/f = 1/o + 1/i where f is the focal length of the lens, o is the object distance, and i is the image distance. Substituting the given values, we get: 1/20 = 1/100 + 1/i Simplifying this equation gives: 1/i = 1/20 - 1/100 = 0.04 i = 1/0.04 = 25cm Therefore, the distance from the film at which the lens must be set to produce a sharp image of an object 100cm away is 25cm, which corresponds to option (C) in the given choices.