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Question
Explain the following term related to spherical lenses: focal length
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Solution
Focal Length:-
The focal length of a lens is the distance between optical centre and principal focus of the lens.
RELATED QUESTIONS
One half of a convex lens of focal length 10 cm is covered with a black paper. Can such a lens produce an image of a complete object placed at a distance of 30 cm from the lens? Draw a ray diagram to justify your answer. A 4 cm tall object is placed perpendicular to its principal axis of a convex lens of focal length 20 cm. The distance of the object from the lens is 15 cm. Find the nature, position and the size of the image.
What is the relation between the focal length and radius of curvature of a spherical mirror (concave mirror of convex mirror)? Calculate the focal length of a spherical mirror whose radius of curvature is 25 cm.
A concave lens produces an image 20 cm from the lens of an object placed 30 cm from the lens. The focal length of the lens is:
(a) 50 cm
(b) 40 cm
(c) 60 cm
(d) 30 cm
Write true or false
A virtual image formed by a spherical mirror is always erect and situated behind the mirror.
Name the kind of mirror used to obtain:
A virtual and enlarged image
AB is the object, A'B' is the image, and MM' is the position of the mirror. Complete the ray diagram showing the formation of the image and find the focal length of the mirror.
