A thin lens has focal length f and its aperture has diameter d.It forms an image of intensity I.Now the central part of the aperture
upto diameter d/2 is blocked by an opaque paper .The focal length and the image intensity will change to?
Focal length will remains same.
Intensity is directly proportional to the area of the aperture of the lens receiving the light.
Total area of the aperture is,
Remaining area after covering,