Question

How will the following be affected by cutting the lens into two halves along the principal axis?
(a) Focal length
(b) Intensity of the image formed by half lens

Answer 1

Hint: Lens follow the phenomenon of refraction. The angle by which light enters and angle by which light exits decides the position at which image is formed by the lens. If the surface by which light enters the surface is convex then the light converges and if the surface is concave then light diverges. The same is for the surface through which the light exits.

Complete answer:
(a) Since, we know the focal length is the distance of the focus point from the center of the lens or the mirror. At this point the parallel rays of light to the principal axis will get merged when they pass through the lens. The focal length is also half of the radius of curvature. Here, we know that the lens is cut along the principal axis so there is no change observed in the focus point since radius of curvature remains same. Therefore the focal length of the lens also remains constant.

(b) The opening within a lens that determines how much light reaches the imaging sensor is known as an aperture. Here, the aperture of the lens gets reduced due to cutting the lens in two halves as we have considered one half of the lens. The decrease in aperture leads to the decrease in the intensity of the image formed.

Note: The radius of curvature refers to the diameter of the sphere from which the lens was carved. Finally, the focal length is the distance between the lens and the focus point. The focal length increases or decreases depending upon the radius of curvature of the sphere. Similarly, aperture decides the intensity of the image formed.