Sign Convention for Convex Lens
When dealing with convex lenses, it is crucial to adhere to a set sign convention to correctly determine the nature and position of the image formed. The sign convention for convex lenses is as follows:

1. Object distance (u):
- The object distance is measured from the optical center of the lens towards the object.
- If the object is placed on the same side as the incident light, the object distance is considered negative (-u).
- If the object is on the opposite side of the incident light, the object distance is considered positive (+u).

2. Image distance (v):
- The image distance is measured from the optical center of the lens towards the image.
- If the image is formed on the opposite side of the incident light, the image distance is considered positive (+v).
- If the image is formed on the same side as the incident light, the image distance is considered negative (-v).

3. Focal length (f):
- For a convex lens, the focal length is considered positive (+f).
- The focal length is the distance from the optical center of the lens to the focal point on the side where the light converges.

4. Height of object and image:
- The height of the object is taken as positive when it is above the principal axis.
- The height of the image is taken as positive when it is above the principal axis.
By following these sign conventions, one can accurately determine the characteristics of the image formed by a convex lens and predict its position and nature.