A combination of two lenses is placed at 25 cm distance from an object, where a convex lens and a concave lens of power 2 D and 3 D respectively forms the lens-combination. What will be the magnification of the image formed by this lens combination ?
Answers
Answer:
it is 3D the answer of the question
Given: A combination of two lenses, one convex lens of power 2 D and a concave lens of 3D. An object is placed at 25 cm from the lens combination.
To find: Magnification of image formed by this lens
Explanation: Object distance (u) = -25 cm
The relationship between power of convex lens and its focal length (f1) in cm is:
Power= 100/f1
=> f1= 100/Power
= 100/2 ( convex lens has 2 D power)
= 50 cm
The relationship between power of concave lens and its focal length (f2) in cm is:
Power= -100/f2
=> f2= -100/Power
= -100/3 ( concave lens has 3 D power)
Let equivalent focal length be f.
=> 1/f = 1/f1 + 1/f2
= f1+f2 / f1*f2
= (50 - 100/3) / 50*-100/3
= (50/3) / (-5000/3)
= -1/100 cm
Let image distance be v.
Now, 1/f = 1/v - 1/u ( lens formula)
=> 1/v = 1/f + 1/u
= -1/100 + (-1/25)
= -1-4 / 100
= -5 / 100 cm= -1/20 cm
Therefore, v= -20 cm
Magnification in lens= v/u
= -20/ -25
= 4/5
The magnification of the image formed by the lens combination is 4/5.