Real vs Unreal Source Refraction Through Lense

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In summary: You are not understanding what virtual images are. A virtual image is an image that is not physically present.
  • #1
Ezio3.1415
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I was having trouble while thinking about the unreal source for refreaction through a lense... In lense light is refracted twice...the real image for the first refraction works as an unreal source for the second refraction... I understand how it is... But fail to feel it...
I mean how would I see the unreal source as? I mean to say what is the diiference between real and unreal source... from a real source light really comes out,it seems to come from a unreal surce bu actually it doesn't... How would I know the difference between this two...

I know there's no difference to us for real and unreal image...

I think I am having a little discomfort to regard the source as unreal...
 
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  • #2
"unreal" is not a term in optics that I am familiar with
An image is "real" if you can put your finger on it, resolve it on a screen etc. and "imaginary" otherwise.

I think the principle you are talking about is where the image formed by the first surface (or a fat lens say) is used as an object for the second surface.

What you are doing is clearer when you use ray-tracing with pencil and paper.
The three principle rays you use are not the only rays - they are just three convenient ones ... but they are only convenient for the first surface. To work out where the actual image will end up, you need to find the three rays from the object which, when refracted by the first surface, will be principle rays for the second surface.

If you do the analysis and then trace - in bold - the actual path of the light through the lens, you should see how working out the location of the image from the first surface helps you do this.
 
  • #3
I have drawn the picture... When using spectacles,I understand how the imaginary source works... Cause the light comes to me such a way that I think its coming from a nearer position... So my eyes can see objects coming from infinitely distant places(when my eyes have defect)...

But my problem is with lens's case... Here after the first refraction light would go a 'certain point'... But for the 2nd refraction it goes to another point... Here how will it seem that the light is coming from that 'certain point'... I solved the equations... proved the laws... But having problems thinking about
"how will it seem that the light is coming from that 'certain point'"
 
  • #4
I think the 2types of image are 'REAL' and 'VIRTUAL'
Real images are formed by converging light rays and can be projected onto a screen
Virtual images are formed by diverging light rays and cannot be projected onto a screen
 
  • #5
The only way to distinguish between the two is that if you actually physically go to the point from which the light rays appear to be coming, you will find nothing there if it is an unreal source. Whereas if it is a real source you will actually find the bulb or lamp there. Thats how mirages are formed btw - with the atmosphere bending light rays to make the source appear closer than it really is, but when you get to the spot where the source appears to be - you find nothing!
From a distance and based on purely optical properties there would not be any way of distinguishing the two.
You only have to try and grab an underwater object to see how deceptive this can be.
 
  • #6
physwizard said:
The only way to distinguish between the two is that if you actually physically go to the point from which the light rays appear to be coming, you will find nothing there if it is an unreal source. Whereas if it is a real source you will actually find the bulb or lamp there. Thats how mirages are formed btw - with the atmosphere bending light rays to make the source appear closer than it really is, but when you get to the spot where the source appears to be - you find nothing!
From a distance and based on purely optical properties there would not be any way of distinguishing the two.

This is incorrect. Some images are at infinity...you cannot go there.
The images are called REAL or VIRTUAL
I have grabbed many underwater objects
Spear fisherman have caught many fish
 
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  • #7
Ezio3.1415 said:
I have drawn the picture... When using spectacles,I understand how the imaginary source works... Cause the light comes to me such a way that I think its coming from a nearer position... So my eyes can see objects coming from infinitely distant places(when my eyes have defect)...

But my problem is with lens's case... Here after the first refraction light would go a 'certain point'... But for the 2nd refraction it goes to another point... Here how will it seem that the light is coming from that 'certain point'... I solved the equations... proved the laws... But having problems thinking about
"how will it seem that the light is coming from that 'certain point'"

Light will appear to be scattered from the image position.
So you can see how the light gets through the optical system ... you traced the actual path of the light ray. Then to see why it appears to be coming from "that certain point", all you need to do is trace at least two exiting rays back in a straight line.

Your visual system basically does ray-tracing from the light that hits your eyes to work out where stuff is.
 
  • #8
"Your visual system basically does ray-tracing
from the light that hits your eyes to work out
where stuff is."

That is the main thing... I found it out myself by thinking how images are formed... And I fully agree with physwizard ...

I did what u told me before... But I fail to grasp how I can observe the source to be behind me... For say, u are sitting in front of a lense... I light a torch from the other side... Light gets refracted and reaches u... For the first refraction I am the source... And light is going towards a certain point... Now if u were at that point where would u see me? At my place or a little higher... (I don't think our eye can trace lens rays back so I think a little higher? Am I wrong? But when u look at me u will be looking through the lense... So?)
However, after the second refraction light reaches u,now how will u say that "certain point" is ur source... How will ur brain apprehend the source to be behind u?

Really confused... :(
 
  • #9
I fail to grasp how I can observe the source to be behind me.
You cannot.
Light rays diverge from the image. Diverging light has to hit your eye for you to be able to see an image.
 
  • #10
U r right... I am saying then how will u say the certain point is ur source?

And what's ur answer abt my other ques...
 
  • #11
The source of light is the glowy thing.
The object is where the physical light rays diverge from.

If you do not know what is between you and the source/object, then there is no way to tell where it is. just by looking at it. All you can see is the image.
Usually, however, we have some ideas about this that let is make refined guesses. If we've set up the optical equipment, then it is simple. That is why you are being taught all this stuff about optics - and, for tha matter, physics - so you'll have the tools to figure out real world situations which are less cut-and-dry.
 
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  • #12
can u please elaborately describe the true and seemingly position of source while refracting through a lense... I mean where the source really is and where it seems to be...
 
  • #13
What do you mean by "source"?
Light rays arriving at the eye appear to the observer to diverge from the image.

You've seen ray diagrams done before surely?
How would you normally locate the image?

Here's one for two thin lenses:

twolenssystem002.gif


... the lenses are the vertical lines.
To an observer to the right of the I2 position, the three principle rays drawn (and all the others) will appear to diverge from the head of the arrow drawn at the I2 position.

Image comes from this "optics tools" website
 
  • #14
I thought about it and understood it... Actually I was confused about unreal source for the 2nd refraction and that led to other ones...

We know that a certain thing reflects light and we see it... So when this phenomenon is happening from any point we think the thing is there... For lense after the first refraction light was converging to a certain point... That would be the image,seeming position of source... But after 2nd refraction the image is set nearer... There the certain point is working as a source... Hence unreal source term is used as for real there's none there...

And another question... Suppose the observer is nearer the image point... Now where will he see the source?
 
  • #15
I mean where he will think the source to be...
 
  • #16
You keep saying "source" - I don't know what you mean?
I cannot help you if you won't answer questions.
 
  • #17
My last question was---
"the observer is nearer the image point... Now where will he see the source?"

Here by source I mean the true source of light... The image is there where light meet and I think the source to be there... In this case, the point where the image is created is behind me... So where will I see the source to be?
I think I will see the source(from where light is created) to be just a little up from its actual position...
 
  • #18
Okay now that I read my question,it seems really vogue... I apologise... I should choose my words more wisely... My ques should be---

"the observer is nearer to the lense than the image point(point where light rays were converging)... Now
where will he think the light rays are coming from(diverging from)?"
 
  • #19
Oh OK :
a magnifying glass is a converging lens - it produces real inverted images of distant objects.
But it you hold it right up to your eye to look at a distant object, the image position is clearly behind your head someplace isn't it? So what do you see? (If you havn't done it before, go find a magnifying glass and do it.)

Is that the sort of thing you are thinking of?
 
  • #20
Yes that's what I am asking for...

will it get blurry?
 
  • #21
Do it and see :)
 
  • #22
Ezio3.1415 said:
Okay now that I read my question,it seems really vogue... I apologise... I should choose my words more wisely... My ques should be---

"the observer is nearer to the lense than the image point(point where light rays were converging)... Now
where will he think the light rays are coming from(diverging from)?"

I think you should start off by using the correct terms ("Virtual Image" and "Object") in your posts. If you google "Image formation + lens" you will find many links which use the correct words.
Your question is a very basic one and the answers are, I think, available on many sites, where you will find dozens of diagrams showing the way images (real and virtual) are formed. This is only 'O Level Physics'.
 
  • #23
I did the experiment... The words I were watching with my magnifying glass appeared to be okay...

The light rays that are converged by the lense are not changing their direction... so I will always observe the image to be a little behind the source and taller... My position doesn't matter... But I will see blurry image if the image is nearer than 25 cm ...

Do I appear to be a graduate student? centaur sophie :p

Actually English is not my first language... However, I would try using conventional words as much as possible...

Thank you very much for the discussion and patience... Simon :-)
 
  • #24
Ezio3.1415 said:
I did the experiment... The words I were watching with my magnifying glass appeared to be okay...
Try the following:

1. Put the glass to your eye, look at objects far as well as near objects through it.
2. Hold the glass at arms length, look at far and near objects through it while holding it at arms length.
See any difference?
3. start with the glass at arms length, then slowly bring it closer to your eye while looking through it at the same distant object.

(note: for a far object 5-10m should be OK. for near, try <10cm)

You should also be able to work out the focal length of the glass.

The light rays that are converged by the lens are not changing their direction...
"converging" means the light rays change direction in the lens.
so I will always observe the image to be a little behind the source and taller...
You mean the image will be behind the object?
My position doesn't matter... But I will see blurry image if the image is nearer than 25 cm ...
"...nearer than 25cm" to what?
 
  • #25
Ezio3.1415 said:
I did the experiment... The words I were watching with my magnifying glass appeared to be okay...

The light rays that are converged by the lense are not changing their direction... so I will always observe the image to be a little behind the source and taller... My position doesn't matter... But I will see blurry image if the image is nearer than 25 cm ...

Do I appear to be a graduate student? centaur sophie :p

Actually English is not my first language... However, I would try using conventional words as much as possible...

Thank you very much for the discussion and patience... Simon :-)

If you were a graduate student you would possibly not be asking these questions in the way you are but, as with most Science, there is a certain minimum requirement of basics if you want a reasonable explanation of things. O level was for 14-16 year olds. You seem to be wanting a non-mathematical answer to something which is actually quite mathematical - in that it involves geometry and formulae.
If we don't share the same (accepted) vocabulary for the subject then there is a great risk that we will not understand each other. Looking at a link like this one will give you an idea of the conventional terms used and how simple lenses work. It is worth more than many paragraphs of question and answer. This part of optics is definitely Quantitative rather than Qualitative and the numbers are very relevant - hence the formulae.
If you find you can't make sense of that link then we may have a problem. Feel free to ask further questions about parts of it (or one of the many alternatives) because it will allow us to address specifics and help you sort them out in your mind.
 
  • #26
Actually I didn't read much optics(in English) besides my text... So I am struggling to express what I want to say... What I am supposed to express by a 'word' , now I have to describe that using a sentence... And I am writing messy sentences... Simon totally misunderstood my last post(which was my mistake)... However, I got out of the confusion I was in before... And currently I am busy with an exam... Hope to continue or revisit the ques later...

Thank you Simon & Sophie...
 

What is real and unreal source refraction?

Real source refraction is the bending of light as it passes through a medium, such as a lens or water. Unreal source refraction is an optical effect caused by the curvature of a lens or other object, resulting in a distorted image.

How does light refract through a lens?

When light passes through a lens, it is slowed down and bent due to the change in density. This bending of light is called refraction and allows the lens to focus the light onto a specific point, creating an image.

What is the difference between real and virtual images?

A real image is formed when light rays actually converge at a point, creating a clear and sharp image. A virtual image is formed when light rays only appear to be coming from a certain point, but do not actually converge. Virtual images are usually distorted and cannot be projected onto a screen.

How does refraction affect the appearance of objects?

Refraction can make objects appear larger, smaller, or distorted depending on the type of lens and the angle at which the light passes through it. This is why objects may appear differently when viewed through glasses or a magnifying glass.

What are some practical applications of refraction through a lens?

Refraction through a lens is used in many everyday objects, such as glasses, cameras, and microscopes. It is also used in medical procedures, such as eye surgeries and laser treatments. In addition, refraction is essential in the field of optics and is used in the design of telescopes, binoculars, and other optical instruments.

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