In the following figure, A, B, C are three point light source positions with respect to the obstacle and the screen. Which of these light source positions will result in the longest shadow of the obstacle on the screen?

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TestHub · Accepted Answer

The sources lie on one vertical line, at the same horizontal distance $D$ from the obstacle.

The screen is at distance $L$ beyond it.

Shadow length $= ℓ \frac{D + L}{D}$ by similar triangles, with $ℓ$ the obstacle length.

This depends only on the horizontal distances, not on the height of the source.

All three shadows are of the same length.

Ans. (D)

Physics - Geometrical Optics Question with Solution | TestHub

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