What happens to the effective power of a plus lens when it is moved closer to the eye?

• A. Increased power
• B. Decreased power
• C. No change in power
• D. Power becomes negative

Answer: (B)

When a plus lens is moved closer to the eye, the effective power of the lens decreases. This phenomenon can be understood through the concept of effective focal length and the lens formula.

A converging lens, such as a plus lens, has a specific focal length that determines how it converges light. As the lens gets closer to the eye, the distance between the lens and the retina decreases, which effectively increases the apparent size of the virtual image created by the lens. However, the eye's accommodation mechanism also comes into play. The eye has a limited ability to accommodate for changes in distance, and when the lens is too close, it may not be able to focus the image sharply, leading to a perceived decrease in the effective power of the lens.

In practical terms, as the plus lens comes closer to the eye, the effective power it provides in terms of its ability to converge light towards the retina diminishes, often resulting in a blurrier image. Therefore, the correct answer reflects this understanding of optical principles as they relate to lens placement and focusing.