ATP Questions lenses/ Cambridge IGCSE P6 | O levels P4 Explained

In this video two questions are explained. 1) 0625/62/O/N/17 (Q3)
(2) 5054/42/M/J/23 Q3 | Full explanation of Converging lens ATP questions | Graphs for lens questions are plotted.
To find the focal length of a convex lens by plotting graphs between u and v or between 1/u and 1/v Object distance and image height follow the steps
1. Fix the convex lens in the holder.
2. Use the lens to focus an object like a tree on a white screen or a wall.
3. Precisely focus the image of the object on the wall or screen until a sharp image is obtained.
4. Calculate the distance between the lens and the wall or screen. It will be the rough focal length of the lens.
5. Mount the holder with the lens in a locked upright, and place the upright at the 50cm mark.
6. Tune the orientation of the lens in such a way that its surface is perpendicular and vertical to the optical bench’s length.
7. Maintain the upright fixed in the above position throughout.
8. Use the thin optical needle as the object (O). Fix it in the outer, laterally movable upright close to zero ends.
9. Adjust the illuminated object upright, and place it at a distance close to 1.5 times the acquired approximate focal length of the lens.
10 . Adjust white paper used as screen at a distance where clear well defined image is obtained