A concave lens is cut vertically into two equal parts. What will be the focal length of each plano-concave lens obtained ?

A concave lens, when cut vertically into two equal parts, results in two plano-concave lenses. To understand the focal length of each of these new lenses, we can refer to the properties of lenses.

Focal Length of the Original Lens

The focal length of a concave lens is negative, indicating that it diverges light. Let's denote the original focal length as f.

Effect of Cutting the Lens

When the lens is cut vertically, each half retains the same curvature on one side and becomes flat on the other side. The focal length of a lens is determined by its curvature and refractive index.

Calculating the New Focal Length

For a plano-concave lens, the focal length can be calculated using the lens maker's formula. When the lens is halved, the effective focal length of each new lens becomes:

• Focal Length of Each Half: The focal length of each plano-concave lens will be f/2.

Final Result

Thus, if the original concave lens had a focal length of f, each of the resulting plano-concave lenses will have a focal length of f/2.