Which formula represents the Lensmaker's formula?

The Lensmaker's formula is given by the equation stating that the reciprocal of the focal length (f) of a lens is equal to the product of the refractive index difference (n - 1) and the sum of the reciprocals of the lens radii (1/r₁ + 1/r₂) for lenses in air. This relationship arises from the principles of refraction and is pivotal in understanding how lenses bend light to focus images.

The correct formulation reflects how the curvature of the lens surfaces (indicated by the radii of curvature, r₁ and r₂) and the material of the lens (indicated by the refractive index n) combine to determine the focal length of a lens. This formulation reveals that a lens that is more curved (smaller radii) will have a shorter focal length, while a lens with a higher refractive index will also impact the convergence of light.

This fundamental formula is crucial in optics, especially in applications such as photography, vision correction with glasses, and designing optical instruments. Understanding the correct Lensmaker's formula helps students grasp the necessary concepts in optics for their physics examinations.