Understanding Reflection of Light on a Concave Mirror

[SHASHWAT PRATAP SING]

My Basic Question is-
Why can we see our inverted and real image inside a concave mirror when the image is formed in front of it and not behind?

If you say that our eyes tries to image the real image formed by mirror on the mirror itself then-

Imagine a situation where we have a concave mirror of large size and we ourself is object and we are directly seeing in the concave mirror and moving backwards so when I stand between focus and pole I see my virtual image slowly when I move backward between focus and centre of curvature then my image must be forming behind me then how my eyes are able to see my real image in the mirror….

Sir to image the real image my eyes must see the image first but in this case how without seeing the image my eyes can see the real image in the mirror it self HOW IS IT HAPPENING …..
Consider this video on youtube -https://youtu.be/7zv-4Zh-9R4

Please answer me in detail... sir i am eagerly waiting for answers

 

[kuruman]

Summary:: Please Explain me this problem in detail...

My Basic Question is-
Why can we see our inverted and real image inside a concave mirror when the image is formed in front of it and not behind?

If you say that our eyes tries to image the real image formed by mirror on the mirror itself then-

Imagine a situation where we have a concave mirror of large size and we ourself is object and we are directly seeing in the concave mirror and moving backwards so when I stand between focus and pole I see my virtual image slowly when I move backward between focus and centre of curvature then my image must be forming behind me then how my eyes are able to see my real image in the mirror….

Sir to image the real image my eyes must see the image first but in this case how without seeing the image my eyes can see the real image in the mirror it self HOW IS IT HAPPENING …..
Consider this video on youtube -https://youtu.be/7zv-4Zh-9R4

Please answer me in detail... sir i am eagerly waiting for answers

To see the tip of the ombrella, the observing eye must be as shown below. You cannot see something unless your eye intercepts diverging rays and refocuses them on your retina.

 

[SHASHWAT PRATAP SING]

Sir I thnk you didn't understand my question-
Imagine a situation where we have a concave mirror of large size and we ourself is object and we are directly seeing in the concave mirror and moving backwards so when I stand between focus and pole I see my virtual image slowly when I move backward between focus and centre of curvature then my image must be forming behind me then how my eyes are able to see my real image in the mirror….

Sir to image the real image my eyes must see the image first but in this case how without seeing the image my eyes can see the real image in the mirror it self HOW IS IT HAPPENING …..

THE PHOTO WAS JUST AN EXAMPLE...

SIR IN MY QUESTION JUST I MYSELF IS VIEWING ME IN THE CONCAVE MIRROR AND MOVIENG BACKWARD
SO WHEN I COME BETWEEN FOCUS AND CENTER OF CURVATURE MY REAL IMAGE WILL BE FORMED BEHIND MYSEF BUT HOW STILL I AM ABLE TO SEE MYSELF IN THE CONCAVE MIRROR HOW?
MY REAL IMAGE MUST BE FLOATING IN AIR BEHIND ME BUT STILL MY EYES ARE ABLE TO SEE IT IN THE MIRROR...HOW

 

[jbriggs444]

SIR IN MY QUESTION JUST I MYSELF IS VIEWING ME IN THE CONCAVE MIRROR AND MOVIENG BACKWARD
SO WHEN I COME BETWEEN FOCUS AND CENTER OF CURVATURE MY REAL IMAGE WILL BE FORMED BEHIND MYSEF BUT HOW STILL I AM ABLE TO SEE MYSELF IN THE CONCAVE MIRROR HOW?
MY REAL IMAGE MUST BE FLOATING IN AIR BEHIND ME BUT STILL MY EYES ARE ABLE TO SEE IT IN THE MIRROR...HOW

Lower case, please. We are all friends here. There is no need to shout.

As I understand it, you are looking into a large concave mirror and trying to observe your own reflected image. The tree is irrelevant.

In the third scenario in the illustration in your original post, you are standing close to the mirror. Close enough that the real image forms behind you. But far enough away that it is a real image behind you rather than a virtual image in front of you.

You ask about your ability to see the real image despite the fact that it is behind you.

@kuruman has remarked that you can only observe an image if it impinges on your eyes as diverging rays. This is not entirely correct. Your eyes normally see by having the lens in the eye focus rays which are diverging as they hit the pupil so that they converge in sharp focus on the retina. In particular, rays from one illuminated point where light emanates (or from one point on an image through which light passes or seems to pass) are focused sharply at one point on the retina.

This works for converging rays as well in either of two manners:

1. The lens in the eye has a variable focal length. The focal length can be tightened to allow nearby objects to be sharply imaged at the retina. Or it can be relaxed to allow far-away objects to be sharply imaged at the retina. Relax it a little bit past infinity and converging rays corresponding to real images near minus infinity can be sharply imaged at the retina.

2. Even if the lens in the eye cannot relax far enough, you can nearly focus converging rays and get a non-sharp image on the retina. Worst case in bright light you can narrow the pupils and still get the effect of a pinhole camera.

 

[Vanadium 50]

Lower case, please.

He's an American. When there is a language barrier, the solution is to repeat, only louder.

 

[jbriggs444]

He's an American. When there is a language barrier, the solution is to repeat, only louder.

Hey, I resemble that remark!

Way too often. :-(

 

[SHASHWAT PRATAP SING]

Sir first of all sorry from myside as i did'nt mean to speak louder in capital letters sorry sir...

Sir in my question I am the only observer and watching myself in a large concave mirror so when i am standing between the focus and centre of curvature my real image is formed behind me and must be floating in air behind me but how my eyes are able to see my real image in the concave mirror
As to get the converging or Diverging rays from the real image to my eyes my eyes must see my real image first...
The photo which I shared was just an eample to say that when we stand between the centre of curvature and focus our image forms behind us...

 

[ZapperZ]

Sir first of all sorry from myside as i did'nt mean to speak louder in capital letters sorry sir...

Sir in my question I am the only observer and watching myself in a large concave mirror so when i am standing between the focus and centre of curvature my real image is formed behind me and must be floating in air behind me but how my eyes are able to see my real image in the concave mirror
As to get the converging or Diverging rays from the real image to my eyes my eyes must see my real image first...
The photo which I shared was just an eample to say that when we stand between the centre of curvature and focus our image forms behind us...

First of all, do you understand that your eyes CANNOT form a focused image if the light rays are converging when they enter your eyes? This means that the light rays must either be parallel or diverging for you to see a focused image with your eyes.

Second, you are throwing out the word "real" here without regards to how they are used in optics and in characterizing images. Your eyes cannot form a focused image on your retina if the light rays are about to form a real image on a screen. This means that if you replace the screen with your eyeballs, you will not see a focused image on your retina.

What this means is that the human eye can only see a focused image on the retina from virtual images. If the image is going to be virtual, only then is there a possibility that your eyes can focus it on your retina.

Why? Because our eyeballs have their own "convex" lenses! These lenses have variable focal lengths because of the muscles attached to them than can change their shapes.

It is unclear if this is something you have understood.

Zz.

 

[SHASHWAT PRATAP SING]

I am not saying to get the converging rays directly into my eyes my main question is how my eyes can see a real image of myself which is formed behind me(As I am standing between focus and centre of curvature) in the concave mirror Please try to understand what I am saying please...

 

[ZapperZ]

I am not saying to get the converging rays directly into my eyes my main question is how my eyes can see a real image of myself which is formed behind me(As I am standing between focus and centre of curvature) in the concave mirror Please try to understand what I am saying please...

First of all, your description is VERY confusing. Are you the person holding the umbrella, or are you the eyeball? You can't be at two different locations at the same time. This is not quantum mechanics.

So who's viewing who? And how are you viewing this? Did you put a screen at a specific location to view the image, or are you using an eyeball? See how confusing this is from OUR perspective of what you have written?

Zz.

 

[kuruman]

I am not saying to get the converging rays directly into my eyes my main question is how my eyes can see a real image of myself which is formed behind me(As I am standing between focus and centre of curvature) in the concave mirror Please try to understand what I am saying please...

If the real image is formed behind you, you will not be able to see it even if you have eyes in the back of your head. You need to place your eye so that the point where the image is formed is between your eye and the mirror. Then the rays (here from the tip of the umbrella) converge into the formation point, get a chance to diverge and then go through your eye lens to become focused on your retina.

 

[jbriggs444]

If the real image is formed behind you, you will not be able to see it even if you have eyes in the back of your head.

As I have already written, this is incorrect. Or is dependent on details of how one interprets the phrase "sees a real image". Certainly one can view something that looks like a person's reflection.

You have a set of rays that would have converged behind the viewers head. The convex lens in the eye causes these rays to converge more strongly and come into focus at an image plane at or near the retina. That is all that is required to see an image -- a pattern of illumination on the retina that matches the shape of the original object.

In some reasonable sense, what you actually "see" is a real image at (or near) the retina.

 

[SHASHWAT PRATAP SING]

Sorry everyone I didn't explained my question well,forget about that umbrella image...

These images are exactly what I am talking about...
Imagine a situation where we have a concave mirror of large size and we ourself is object and we are directly seeing in the concave mirror and moving backwards so when I stand between focus and pole I see my virtual image slowly when I move backward between focus and centre of curvature then my image must be forming behind me then how my eyes are able to see my real image in the mirror….

Sir to image the real image my eyes must see the image first but in this case how without seeing the image my eyes can see the real image in the mirror it self HOW IS IT HAPPENING …..
In my question just I myself is viewing me in the concave mirror and moving backwards.
So when I come between focus and the centre of curvature my real image will be formed behind myself but how still I am able to see myself in the concave mirror HOW?
My real image must be floating in air behind me but still my eyes are able to see it in the mirror...HOW

 

[A.T.]

This might help:

 

[jbriggs444]

then my image must be forming behind me then how my eyes are able to see my real image in the mirror….

You really need to work on your description. Say exactly what you mean. Say exactly what each picture shows.

Try to avoid phrases like "image must be forming". If you are standing still the image is either there or it is not. It is not "forming". Try to avoid phrases like "real image in the mirror". The real image is not in the mirror. It is behind your head.

You have provided a number of pictures. Let us go through them slowly. Let us identify carefully what they show.

The first picture is of someone standing nose to mirror. There are two locations marked on the floor. One is marked "C". One assumes that this is at the center of curvature of the concave mirror. The other is marked "F". One assumes that this is at the focal length of the concave mirror.

This impression is reinforced by the fact that the distance from the mirror to C is approximately double the distance from the mirror to F.

But you are not asking about the situation in the first picture. So that picture is mostly wasted.The second picture is of someone standing between the focal point F and the center of curvature C. We see a blue shape drawn in space behind the person. One assumes that this is the place where the [inverted] real image of the person would form.

The person stands in the way of some of the reflected light that might otherwise go into forming this real image. As a result, the real image may not be viewable from all angles. However, this detail is irrelevant to the question that we are trying to address. Let us ignore that situation and proceed.The third picture is the same as the first but without the "C" and "F" labels drawn in. We can ignore it.The fourth picture is the same as the second. But instead of "C" and "F" labels and an image drawn behind the person, we have an arrow in front of him pointing toward the mirror.

This would appear to be an attempt to depict the person's line of sight toward the mirror.The final picture appears to have been taken from a little to one side as the man stands in the position depicted in the second and fourth pictures. That is, it was taken while the man is standing between the C and the F. It shows an inverted image.

This appears to be an attempt to show what the person himself sees. I may be mistaken, but that might be the camera's reflection in the person's right hand.If I understand your concern, it is that if we are looking away from a real image, we might not expect to be able to see that image. Certainly, our intuitive expectations learned from everyday life tend to support this. If person is standing behind me, I cannot see them when I am looking toward the front. If an image exists behind me, I might not expect to see it when I am looking toward the front.

This expectation is incorrect. The photographic evidence you have provided demonstrates that it is incorrect.

The light rays that hit your eyes are light rays that would have converged at the real image behind your head. But they did not converge there. Your eyes were in the way. The lens in your eyes (or in your camera) caused them to converge on your retina (or on the photodetector array in your camera) instead.

You "see" the image because the pattern of illumination on the retina (or on the photodetector array) corresponds to the shape of the person.

Human eyes are not designed to be able to clearly image converging light rays. It requires that they relax to a focal length longer than the distance from lens to retina. A focal length equal to the retinal distance would allow one to clearly focus on objects "at infinity". A shorter focal length allows one to focus on objects closer in. A longer focal length allows one to focus on images corresponding to convergent light rays -- that is real images behind the head.

There is no evolutionary call for eyeball lenses that can focus out past infinity. And little technical call for cell phone lenses that can do the same. The cell phone image of the reflected inverted man is not sharp. But with a narrow aperture, one can push the limits.

 

[A.T.]

my real image will be formed behind myself but how still I am able to see myself in the concave mirror HOW?

As @jbriggs444 said: The light that you see never reaches the real image behind you, because your eyes intercept it. But these rays are focused such that your eye/brain interpret is an object where the real image is. To understand it you would have to include the eye with its lens in the ray diagrams.

 

[jbriggs444]

As @jbriggs444 said: The light that you see never reaches the real image behind you, because your eyes intercept it. But these rays are focused such that your eye/brain interpret is an object where the real image is. To understand it you would have to include the eye with its lens in the ray diagrams.

I do not want to pontificate too much on how our brains process distance cues to determine exactly how far away the perceived image seems to be. There are lots of cues that can be used. Lens focus and binocular vision are only two. Occlusion, image size and angle on the landscape are others.

However, it seems clear that the brain will decide that "the image is somewhere in front of me" and not that "the image is somewhere behind me".

Somewhat on-topic anecdote...

Some forty years ago, while I was in graduate school at the University of Illinois lounging in a student commons, I was approached at random by a student who wanted to quiz me about distance perception. He asked me to rank various depth cues by importance. He then proceeded to show me some flash cards and compare distances to objects depicted therein. My ivory tower guesses about depth cues did not match well with the real world results obtained from the flash cards. It was an interesting experience.

 

[A.T.]

However, it seems clear that the brain will decide that "the image is somewhere in front of me" and not that "the image is somewhere behind me".

Yes, but when the brain is familiar with flat mirrors, it can interpret this impression (by comparison) as an object further away from the mirror, than the object actually is.

But limits of our eyes you mention also make it blurry in this case.

 

[SHASHWAT PRATAP SING]

In this image we can see that the person is standing between focus and the centre of curvature, so his real image is formed behind him (in the air)... so sir If a real image exists behind him, he might not expect to see it when he is looking toward in the front (in the mirror).

Then, how is he able to see his real and inverted image in the concave mirror.

You really need to work on your description. Say exactly what you mean. Say exactly what each picture show

Sir @jbriggs444 please help me...

 

[A.T.]

Then, how is he able to see his real and inverted image in the concave mirror.

Have you tried drawing a ray diagram that includes the eye/camera? You can use the simplest pinhole camera model.

 

[sophiecentaur]

MY REAL IMAGE MUST BE FLOATING IN AIR BEHIND ME BUT STILL MY EYES ARE ABLE TO SEE IT IN THE MIRROR...HOW

I understand your problem entirely. It was the same for me at first. Only when I used a mirror could I actually appreciate what's happening.

I think your problem is that you think the image is real and behind you when you can see it. When you get that condition, you are standing near the focus of the mirror and, on either side of that position, you will see an image that's either virtual and behind the mirror (when you're close) or real and in front of you (you're further away). Around that critical point, the image 'explodes' and you don't actually see it - because it's formed behind you. It's only when you go further away that the image position is actually in front of you (near and highly magnified).
Around that position your poor brain has a serious problem and can't actually make sense of what you see.
Note: This effect is most obvious with large mirrors (clearly the radius needs to be large) and the region around the exploding point is quite large. Looking in the bowl of a shiny spoon, you need to put your eye in very close and you can see your eye explode as it goes from inverted to non inverted.

 

[Drakkith]

Imagine a situation where we have a concave mirror of large size and we ourself is object and we are directly seeing in the concave mirror and moving backwards so when I stand between focus and pole I see my virtual image slowly when I move backward between focus and centre of curvature then my image must be forming behind me then how my eyes are able to see my real image in the mirror….

Sir to image the real image my eyes must see the image first but in this case how without seeing the image my eyes can see the real image in the mirror it self HOW IS IT HAPPENING …..

When you are standing closer to the mirror than the (real) image, your eyes are not viewing the image shown in the picture. Your eye is intercepting the rays before they converge and is forming a new image at your retina. Remember that talking about real and virtual images is only one way of understanding optics. If you're ever confused, do a simple raytrace with a couple of rays and see what happens if you place your eye or an imaging device somewhere.

 

[SHASHWAT PRATAP SING]

I understand your problem entirely. It was the same for me at first. Only when I used a mirror could I actually appreciate what's happening.

I think your problem is that you think the image is real and behind you when you can see it. When you get that condition, you are standing near the focus of the mirror and, on either side of that position, you will see an image that's either virtual and behind the mirror (when you're close) or real and in front of you (you're further away). Around that critical point, the image 'explodes' and you don't actually see it - because it's formed behind you. It's only when you go further away that the image position is actually in front of you (near and highly magnified).
Around that position your poor brain has a serious problem and can't actually make sense of what you see.
Note: This effect is most obvious with large mirrors (clearly the radius needs to be large) and the region around the exploding point is quite large. Looking in the bowl of a shiny spoon, you need to put your eye in very close and you can see your eye explode as it goes from inverted to non inverted.

https://www.physicsforums.com/threa...ront-of-it-and-not-behind.990974/post-6362719
This is my main question sir just two post above your post please see it and explain me again please sir...

 

[A.T.]

...explain me again ...

Just read it again maybe.

 

[Drakkith]

https://www.physicsforums.com/threa...ront-of-it-and-not-behind.990974/post-6362719
This is my main question sir just two post above your post please see it and explain me again please sir...

You are not viewing a 'real' image when you are between the focal point and the center of curvature. You are not viewing any image at all, not even a virtual one. You are, instead, inserting your eye into the path of the light before it ever has a chance to come to focus.

The ONLY image formed in this scenario is the one inside your eyeball.

 

[sophiecentaur]

Then, how is he able to see his real and inverted image in the concave mirror.

Because he is standing behind it! If he goes closer, he won't see it. You have to remember that he is his own Object so both Object and Image are moving in and out and that means the 'exploding region' moves - unlike if he was looking at a stationary object. As I have already suggested. Try it with the inside bowl of a spoon and see the behaviour that I have already described.

Just read this, read it and read it again. What is written has been written by several other posters. You seem to be so committed to not understanding that you are walking past the goal without seeing it.
It's all here in plain sight.

 

[A.T.]

The ONLY image formed in this scenario is the one inside your eyeball.

This image inside your eyeball is crucial to what you see in all scenarios. The other real images are only relevant if you want to place a screen there.

 

[sophiecentaur]

I looked around me and found hair on the floor around me. I have been tearing it out!

 

[A.T.]

I looked around me and found hair on the floor around me. I have been tearing it out!

Looking forward to your new avatar picture.

 

[sophiecentaur]

Have you tried drawing a ray diagram that includes the eye/camera? You can use the simplest pinhole camera model.

I just read this again. It's extremely hard to 'see' anything through a pinhole - you tend just to see a pinhole. Moving your head from side to side can give a clue about what's the other side but that technique needs to be 'learned' and the retina is not helping you. A pinhole is actually (imo) a hard thing to appreciate because nothing and everything is in focus, wherever you put the film. The model could be too easy and too hard for the OP, at the same time.

 

[A.T.]

The model could be too easy and too hard for the OP, at the same time.

You can always make the hole bigger and a put a lens in it. But for starters the OP learn to distinguish between the real image formed by the mirror, and the real image in the eye/camera.

 

[ZapperZ]

View attachment 265704
In this image we can see that the person is standing between focus and the centre of curvature, so his real image is formed behind him (in the air)... so sir If a real image exists behind him, he might not expect to see it when he is looking toward in the front (in the mirror).

This is why I continue to think that you do not understand ray optics yet.

There is no real image anywhere in this scenario! This means that there isn't a real image behind him! Again, if you done a ray diagram and shown it to us, we can easily dispel this!

View attachment 265705
Then, how is he able to see his real and inverted image in the concave mirror.
Sir @jbriggs444 please help me...

He is not seeing a real image. His eyes cannot focus on light rays that is about to form a real image. I have said this numerous times! The light rays are DIVERGING, and the lens in his eyes is the one focusing the image onto his retina.

The image is also NOT behind him. It is behind the mirror.

Since you have refused to draw your own ray diagram, I did it.

Notice where the object is, where the VIRTUAL IMAGE is. There are no real image anywhere here. The virtual image is behind the mirror, not behind the object.

Since the light rays are DIVERGING after they have been reflected and when they go through the object, if the object is a person, then his eyes see diverging light rays, and the lens in his eyes will focus on those rays to cause a focused image on his retina. This enables him to "see" the virtual image at an apparent distance behind the mirror.

BTW, why do you automatically assume that everyone who answers your question on Physics Forums must be and can only be male? You have never seen women physicists or engineers or scientists before?

Zz.

 

[A.T.]

Since you have refused to draw your own ray diagram, I did it.

He is asking about the case where the object is between the curvature center and the focus:

Here you have a true image behind the object. But for what you see, only the true image on your retina matters.

 

[ZapperZ]

He is asking about the case where the object is between the curvature center and the focus:

https://www.physicsforums.com/attachments/265733

Here you have a true image behind the object. But for what you see, only the image on your retina manners.

Probably, but I needed him to show a ray diagram first, and I'm showing him the simplest case to establish some "baseline" here. I'm hoping to "goad" him to actually show a ray diagram by showing him mine.

Zz.

 

[A.T.]

He is asking about the case where the object is between the curvature center and the focus:

Here you have a true image behind the object. But for what you see, only the true image on your retina matters.

Looking at that diagram again: Since the real image on the retina is flipped, you should see yourself not flipped in this case. Assuming your eye can still focus these rays.

So the distance at which the image on your retina flips, is not the focus point but the center of curvature. The focus point is merely the distance at which the not flipped virtual image behind the mirror is replaced by a real image behind you.