What is the relationship between lens strength and focal length?

The correct answer highlights a fundamental principle of optics regarding lenses. Lens strength, often referred to as optical power, is defined mathematically as the reciprocal of the focal length. This relationship indicates that a lens with a shorter focal length has a greater strength, meaning it bends light more sharply and can converge or diverge rays more effectively.

In practical terms, when you have a lens, its strength determines how much it can focus or spread light, which is critical in applications such as eyeglasses, cameras, and telescopes. For instance, a strong lens (with a short focal length) is necessary for correcting vision problems, while a weaker lens (with a longer focal length) would be used for other optical applications where less refraction is needed.

Understanding this relationship is key for students as it impacts how various types of lenses are designed and used across different optical systems.