The lens displacement method is a widely used technique for determining the focal length of a thin lens, grounded in the principles of the thin lens formula. This formula is expressed as:

where $f$ represents the focal length of the lens, $u$ denotes the object distance, and $v$ indicates the image distance.

To implement the lens displacement method, a thin convex lens is securely positioned on a stand, and a distant object is placed in front of it. The object’s position is adjusted until a clear image is formed on a screen located behind the lens. At this point, the distances from the lens to the object ($u$) and from the lens to the image ($v$) are measured accurately.

The focal length of the lens can be calculated using the thin lens formula. To enhance the precision of the measurement, the experiment is repeated after displacing the lens by a small distance. Again, the new object and image distances are recorded, and the focal length is calculated based on these new measurements.

By averaging the focal length results from both measurements, a more accurate estimate of the lens’s focal length can be obtained. The lens displacement method is not only straightforward but also an effective approach for determining the focal length of a thin lens, making it a common practice in physics experiments and optics research.