Size of light source and sharpness of shadow | Light | Physics

This activity focuses on the effect that the size of a light source has on the nature of the shadow of an object. A narrow light source like the one used in the video produces a sharp shadow as shown. A wide source, on he other hand, produces a diffuse shadow consisting of completely dark region known as the umbra and a half lit half shadow region known as the penumbra.

[proactivex]

Watched two videos by photographers on this. They don’t understand the why. They think there’s two separate reasons why you get sharp shadows.

[danieljust]

The diffused shadow is caused by scattered light, the light reflected from the walls and the screen, and from the side of the ball facing the screen. The diffusion is simply interference.

In the first experiment (the bulb is covered and goes through the hole) you assured that the light is quasi parallel when hits the object producing shadow larger than the object itself. In the second part the shadow produces umbra/preumbra due to interference and the main shadow is smaller.

[-Phil]

Thus: The Aug 21, 17 Sun was "narrower" than the moon ==> 70 mi solar eclipse "sharp"-umbra' width larger than the moon.
(Aka, moon < 70 mi wide)

[scottlavalle]

You can't make a scale model of all 3 entities. Too far away.

[graceanderson]

Nice video, but can someone please tell me why this happens? Maybe I missed that this video is part of a series or maybe he gave a link, but I can't seem to find either. D:

[rixiizz]

WHY THIS TEACHES ME NOTHING JUST ANSWER ME WHY!!