Which one of the following combinations of source and screen would pro

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

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A point source and an opaque screen

An extended source and an opaque screen

A point source and a transparent screen

An extended source and a transparent screen

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This question was previously asked in

UPSC CDS-2 – 2020

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The sharpness of a shadow depends on the size and type of the light source and the properties of the screen. A point source of light produces a sharp shadow with a well-defined edge, called the umbra. An extended source of light produces a shadow with a dark central region (umbra) and a partially illuminated region around it (penumbra), resulting in a blurry edge. An opaque object is necessary to block the light and form a shadow. The screen needs to be opaque to display the shadow, as light would pass through a transparent screen. Therefore, the combination of a point source and an opaque screen produces the sharpest shadow of an opaque object.

A point source of light creates a sharp shadow (umbra) without a penumbra, unlike an extended source which creates both umbra and penumbra.

The size and distance of the object and the screen also affect the shadow’s size and shape, but the sharpness is primarily determined by the nature of the light source (point vs. extended) and the screen (opaque vs. transparent). An opaque screen is essential to intercept the light and make the shadow visible.

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