Which of the following combinations of source and screen would produce the sharpest shadow of an opae object?

A shadow's sharpness is primarily determined by the size of the light source and the nature of the screen. A point source of light produces a shadow with sharp edges because it creates only an umbra (a region of total darkness) without a penumbra (a region of partial darkness). In contrast, an extended source creates a blurry shadow consisting of both umbra and penumbra. Furthermore, for a shadow to be clearly observed and sharp, it must be cast on an opaque screen. Opaque materials do not allow light to pass through, ensuring a distinct contrast between the dark shadow and the lit surface [1]. Transparent screens allow light to pass almost completely, making them unsuitable for capturing a distinct, sharp shadow [1]. Therefore, the combination of a point source and an opaque screen yields the sharpest shadow.

Sources

1. [1] Science-Class VII . NCERT(Revised ed 2025) > Chapter 11: Light: Shadows and Reflections > In a Nutshell > p. 165