Ekta makes a pinhole camera from a box and points it at a tree
Ekta makes a pinhole camera from a box and points it at a tree. On its tracing-paper screen, the tree appears upside down. Ekta says this happens because light travels in straight lines: light from the top of the tree passes through the hole and lands at the bottom of the screen. Sahil says the hole is too big — with a smaller hole, the tree would appear the right way up. Whose explanation is correct?
Who do you think is right? Pick one.
The answer: Ekta is right, rays travelling in straight lines cross over at the hole
Why
Sahil is correct that the size of the hole matters — but it changes the sharpness of the image, not which way up it is. A big hole lets light from each point of the tree spread over a patch of the screen, so the image goes blurry; a smaller hole gives a sharper (though dimmer) image. Neither turns it the right way up. The flip comes from light travelling in straight lines. Light from the top of the tree heads downward to the hole and carries straight on, so it lands low on the screen; light from the bottom of the trunk heads upward through the hole and lands high. The rays cross at the hole, so top and bottom swap — and so do left and right. Test: make the hole smaller with a pin and the image becomes sharper, but the tree stays upside down. Ekta is right: the image is upside down because light travels in straight lines and the rays cross at the pinhole.
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