Question :An object is kept at a distance of 1m from a lens of power +2D:
(i) Identify the type of lens.
(ii) Calculate the focal length and distance of the image formed.
The correct answer is -(i) The given lens is a convex lens or a converging lens because its power is positive (+2D). (ii) The formula for calculating the focal length of a lens is:
1/f = 1/v – 1/u
Where f is the focal length, u is the object distance, and v is the image distance. We know that u = 1m and the power of the lens is +2D. The formula for power is:
P = 1/f
Therefore, f = 1/P = 1/2 = 0.5m.
Now, we can use the lens formula to calculate the image distance as:
1/f = 1/v – 1/u
1/0.5 = 1/v – 1/1
v = 0.67m
Therefore, the focal length of the lens is 0.5m and the image is formed at a distance of 0.67m from the lens.
