A diverging lens is used to permit clear vision of an object placed at infinity. The focal length of the lens is -100 cm.
The focal length is half of the radius of curvature of the focal lens.
By the lens maker formula,
1/f = 1/v +1/u
where, v is the image distance and u is the object distance.
Give, the object is at infinity and the image must form at 100 cm, the the focal length will be
1/f = 1/ -100 + 1/∞
f = -100 cm
The focal length must be -100 cm for the diverging lens.
Learn more about focal length.
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