An object is placed on the principal axis of a convex lens of focal length 10 cm. If the distance of the object from the lens is 30 cm. What is the distance of the image formed?

First, let's identify what we know:
* Focal length (f) = 10 cm This tells us how strongly the lens bends light.
* Object distance (u) = 30 cm This is the distance between the object and the lens. Remember to use the sign convention! For a convex lens, u is usually taken as negative. So, u = -30 cm
We need to find:
* Image distance (v) = ? This is the distance between the image and the lens. This is what we want to calculate.
Now, let's use the lens formula:
1/f = 1/v - 1/u
Plug in the values:
1/10 = 1/v - 1/(-30)
1/10 = 1/v + 1/30
Now, let's solve for 1/v:
1/v = 1/10 - 1/30
1/v = (3 - 1)/30
1/v = 2/30
1/v = 1/15
Therefore, v = 15 cm
So, the correct answer is Option B: 15 cm