A thin lens focal length \[{{f}_{1}}\] and its aperture has diameter d. It forms an image of intensity I. Now the central part of the aperture upto diameter \[\frac{d}{2}\] is blocked by an opaque paper. The focal length and image intensity will change to [CPMT 1989; MP PET 1997; KCET 1998]

• A.            \[\frac{f}{2}\] and \[\frac{I}{2}\]                                     
• B.            \[f\]  and \[\frac{I}{4}\]
• C.            \[\frac{3f}{4}\] and \[\frac{I}{2}\]                                   
• D.            \[f\]  and \[\frac{3I}{4}\]