A screen is placed at a distance of 100 cm from an object. The image of the object isformed on the screen by a convex lens for two different locations of the lens separated by 20 cm. Calculate the focal length of the lens used.
Asked by Raj
20th February 2018,
5:52 AM
Answered by Expert
Answer:
The given problem is illustrated in figure. When we fix the location of object and image formed screen, the object to lens ditance u and the image to lens distance v are interchanged to form imgaes by placing the lens at two locations. In the first case object is at a location beyond 2F where F is focal point so that diminshed image is formed. In second case object is between F and 2F and we get enlarged image.
From figure we can see u+v = 100; u-v=20;
solving for u and v we get u=60 cm and v = 40 cm.
focal length f is given by
focal length f = 24 cm
Answered by Expert
20th February 2018,
3:13 PM
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