Here's a Question! - Circle vs. Triangle
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- Опубликовано: 26 сен 2024
- A card with a small triangular hole in it is attached to one end of a meter stick and a piece of paper is attached to the other. The meter stick is pointed towards the sun so that its light passes through the triangular hole and falls on the paper. What shape does the light make on the paper?
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I am Mitrayu from India. Thanks for uploading such videos.
I remember the last solar eclipse that came across my home town. It blew me away how many random shadows showed its shape all around. Thanks for posting!
One way to talk about it is, if your eye were at the position of the paper, what would you see? The triangle is pretty small from where you're looking. Pretty much, the entire triangle will fit in the disc of the sun, which means your eye, at that point, will see a lot of brightness (the paper at that point will be bright), or the entire triangle will miss the sun, so your eye won't see any sunlight from that point, the paper at that point will be dark. What's light and what's dark is pretty much determined by the disc shape of the sun - the paper will show a bright disc.
Nice work, making these videos. They're all good - keep it up.
Not as easy to demonstrate, but if you could do the test again during a partial solar eclipse you no longer get a full circle. It’s so cool!
Well, we'll get two opportunities over the next year or so.
The important factor is distance which brings into question any astronomic assertions which too involve this but cannot be really resolved as those are not at convenient arm’s length.
So, if the hole in the card was larger, would the image be a triangle?
And what would the image be if the paper was closer to the card with the hole in it.
This experiment seems similar to a previous one about a pinhole camera.
Yes, if the hole were larger, then the image would be a triangle. Same thing if the distance were reduced. Imagine for a moment that the card was on the paper. Then the 'spot' on the paper would be identical to the opening in the card.
And, yes, this is very similar to the previous pinhole camera videos. The pinhole need not be circular for everything to work.
For those reading here before guessing - the triangle hole is really small, probably 2 to 3 mm across.
Okay, but WHY? Is it because the sun is round? Is it due to some intrinsic property of white light that makes it naturally spread into a circle shape due to the waves hitting each other? What doesn't it produce a triangular spot? Is it because the sun is so far away that its apparent image is tiny relative to the whole size?
It isn't that the sun is far away - it's that the triangular opening is (relatively) far away from the paper. This is just a pinhole camera and the triangular opening 'looks like' a pinhole when it is sufficiently far away from the paper. If it had been pointed at a light bulb rather than the sun, we'd see an image of the light bulb on the paper. The triangular opening will affect how the overall image is illuminated, but it still projects an image of whatever it is pointed at. Since it was pointed at the round sun, an image of the round sun was seen.
If you want a triangular spot of light, then the opening would either need to be much larger, or much closer, or the paper.
what would happen to the shadow of a triangle from very far away?
Depends on the light source. If it's something that has a tangible size, like the sun, then the shadow is 'fuzzy' because the light is coming from slightly different directions. The shadow becomes less distinct as the distance between the object and the screen increases. At some point, the object will be far enough from the screen that, from the screen's perspective, it appears to be smaller than the light source. At that point, there is no longer a true shadow (a full shadow?) because some part of the light from the source can always strike the screen that's directly behind the object.
If the light source is essentially a point source, then the light rays are essentially parallel and the shadow cast upon a distant screen is always essentially the same size and shape of the object, irrespective of the object's distance from the screen. This can actually be used to measure the size and shape of asteroids in the Solar System. If one happens to pass in front of a star as seen from Earth, observers in different locations can basically trace out chords on the object by timing when they see the star wink out and when they see it reappear.
@@JeffersonLab That's a great explanation. Thanks :)
So, it's about resolution?
In essence.
Circle takes the square?
YES