Two lenses having power of +2D and - 4D. What is the nature & focal length of each lens. An object is kept at a distance of 100cm from each of the above lenses. Calculate the image distance and magnification in each of two cases.
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The value of magnification for convex lens is 1 and for concave lens is 0.2
Explanation:
Given data:
Power of lenses: +2D and - 4D
+2D indicates that the lens is converging lens (convex lens) .
Distance of object p = 1/f
Focal length f = 50 cm
(ii)-4D indicates that the lens is diverging lens (concave lens)
Therefore the focal length is -25 cm
- To calculate the image distance for convex lens
u = -100 cm
f = 50 cm
v = (f x u)/(f-u) = 100 cm
Magnification = 1
- For concave lens :
u = -100 cm
f = -25 cm
v = -(f x u)/(f+u)
v = -20 cm
Magnification = v/u = 20/100 = 0.2
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