Bendy Light
A hole is pierced in the side of a water-filled bottle, so that water streams out as shown above.
When a laser beam is aimed toward the hole, the beam is seen to travel along the curved path of the water stream. What can explain this phenomenon?
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5 solutions
First demonstrated by Amazing 19 Century Scientist John Tyndall who also first provided evidence of Earth's greenhouse effect. See the many more works of Tyndall https://en.m.wikipedia.org/wiki/John_Tyndall
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Interesting to read the inventions and discoveries made by Tyndall. Thanks for sharing!
I shall point out that a small amount of light will escape, because in not all places is the angle of incidence greater than the critical angle. This is why the water jet glows slightly. But if I remember correctly, then as the angle of incidence approaches the critical angle, the proportion of light internally reflected approaches 100%.
The light ray simply does Total Internal Reflection (TIR) while it was falling from the jet.
TIR is the complete reflection of a light ray reaching an interface with a less dense medium when the angle of incidence exceeds the critical angle.
Yes, exactly. But, what about the other options? Can light bend due to gravity?
For TIR to occur the angle of incidence must be greater than the critical angle. Does the level of water or the height of hole make any difference to this experiment?
Its refelcting off
Grt explanation
Light is only affected by gravity is extreme situations as those found in blackholes where gravity theoretically accelerated in an exponential curve. Hence why the event horizon is black because not even light gets through.
Tbf all of these options make sense to a degree. The light does bend due to gravity acting on the water. The light bends due to the refractive nature of the water just like fibre optics. The water air barrier creates the fibre optic effect within the water. And as always any video can be fake.
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The optical fibers have a uniform refractive index. The light bounces off due to total internal reflections.
My immediate response on this is Option 3 (light reflects off the water-air boundary). This would be similar to a situation where you shoot a light beam in a tube or pipe with all its interior surface lined with mirror or reflective surface. The water-air boundary functions as a continuous reflective mirror coating like in a flat mirror and the spontaneous/continuous bouncing of light will be carried all the way to the end of the tube/pipe.
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Ya its the case of Optical Fibres. Optical fibres does so
Why does the light keep bouncing off? Doesn't it require to meet the condition that the angle of incidence must be greater than the critical angle?
Ha! Total Internal Reflection: The principle behind optical fibers :D
The phenomenal is total internal reflection where it happens when light travels from denser region to less dense region.
Elimination method:
Option 1 does not make sense as light is unaffected by gravity. Option 4 is out (need I say more?).
This leaves options 2 and 3.
Option 2 is not true as the refractive index of water does not change with flow.
This leaves option 3.
As far as I know, gravity bends space and so does the path of light. But, obviously, at the location of the experiment, I am sure the gravity won't be so huge to bend the light that much.
Option 4 is not ruled out in any of these arguments. The video is fake.
So it is a total wrong that light travels in straight line (not taking the view of wave). For me since light travel in straighline, curved path should not occur. It should make an angle with two arms (light beam arms here) when coming out of the glass air boundary because of total internal reflection.
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There is no glass -air boundary in the problem. Do you mean water -air boundary instead? Moreover, I don't get what you are trying to convey here, can you elaborate your point?
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oh, i got the question wrong. actually the light beam travelling through water stream that would make the phenomenon right.
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@Amit Chand – Yes, which phenomenon is allowing light to move along the water stream in a curve?
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@Rohit Gupta – The light isn't moving in a curved path - it's moving in a sequence of short, straight paths as a result of total internal reflection. Pranshu's solution explains it best.
"Light is unaffected by gravity'" is not true as an absolute, read Einstein, but we can go with it here. Safe to say they would not fake it, would lose all credibility. #3 makes the most sense.
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I agree, Earth's gravitational field is not strong enough to cause such a big change in the light's trajectory. In this case, the light is moving in straight lines, but it reflects so often that it appears to move in a curved path.
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Regardless of how strong gravity is, it would still bend the path of light much less than that of a jet of water because of the speed difference.
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@Stewart Gordon – Right, if gravity is stronger, then the water jet will also flow down faster. Light still won't be able to escape the water jet.
option 4 is the right one because even when light changes its way it goes on a straight way not in curve one
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Consider a case of an optical fiber, how does light travel in it along the fiber if it is to travel in a straight line?
Gravity bends light!
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Yes, but we rarely get see a significant bending of light by gravity in our daily life.
Actually I stopped at that option if gravity bends light or not, it's after all a fact that even light can't escape black holes due to strong gravity.... But yeah gravity isn't at all that strong here
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That is exactly the point, the option in itself is true in general but not a factor causing this phenomenon.
If refractive index of water does not change then how is it possible that still water gives no shadow (ie most of light is transmitted) but disturbed water gives shadow (ie it does not allow complete light).
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When water is disturbed, parallel light rays no longer make the same angle with the surface of the water, and therefore will be refracted in different directions.
This is an interesting point, but shadows are caused due to reflection and not refractions. Maybe due to the disturbance, the impurities in the water (which were settled at the base in still water) moves around and reflect light to cause a shadow.
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If there are internal disturbances then how can total internal reflection take place as the angle can change each time and critical angle may not be maintained.
The reason answer 1 is wrong is that light travels much faster than any flow of water. And so in the time it takes light to fall 1mm towards the earth due to gravity, it will have moved a great distance horizontally, compared to the distance the water coming out of the bottle will have travelled in the same time frame.
When a light ray moves from a optically denser medium to a rarer medium, (in this case from water to air), it may reflect off the boundary instead of going through it, provided the light ray makes a small angle with the boundary. This is called total internal reflection .
A few reflections are shown in the diagram. The light ray is always straight, but because it makes so many reflections, it appears to move in a curved path.
This phenomenon is used in fiber optics communications, to transmit data at high speeds over long distances. The optical fiber can transmit light even when it is not straight, because it traps most of the light by total internal reflection.