# Why doesn't my reflection follow the inverse square law ?

Discussion in 'The Cesspool' started by Jerimiah, Sep 27, 2021.

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1. ### JerimiahRegistered Member

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I noticed the other day while looking into a mirror from some distance away that my reflection was visually proportional to myself in dimensions . If light follows the inverse square law then how can this be ? Wouldn't my reflection be visually larger ?
Does the inverse square law only apply to projectors ?

confused

3. ### exchemistValued Senior Member

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What inverse square law are you thinking of?

Because it goes in straight lines, light intensity from a point source falls off according to the inverse square law: the density of the rays of light radiating out from a point falls with the square of the distance. That is not going to affect the apparent size of a reflection of an object, though.

5. ### Janus58Valued Senior Member

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While light coming from the different parts of your body does spread out as it travels away from you, only those rays that actually hit the mirror can be reflected by it. In addition, you can only see that light that reflects off of a mirror along a direction that enters your eye. You would no more expect your reflection( off of a flat mirror) to look bigger than you would expect someone a distance from you to look bigger.

7. ### JerimiahRegistered Member

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Hi , thanks for the reply , I am thinking of this : https://en.wikipedia.org/wiki/Inverse-square_law

You are saying this has no affect on my own reflection ?

I find that strangely odd because in my own mirrored reflection I do not see any distortion around the image ! If the light follows the inverse square law and decreases in magnitude 1/d^2 , then I'd have thought we'd see a distortion around the reflected image where the magnitude was weakened ?

8. ### JerimiahRegistered Member

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Hi thanks for the reply . If I place three mirrors in front of me , one to the left , one center and one to the right , my images in all three mirrors are equal in magnitude ?

9. ### Janus58Valued Senior Member

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Yes, The only way to see a larger image is if the surface of the mirror has a concave curve (that's how those magnifying mirrors work.)

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10. ### JerimiahRegistered Member

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I have another question on the left , center and right mirror . The angular vector path the light travels to the left and right mirror is a greater distance than the vector path to the center mirror. I am assuming because of the speed of light constant , that the reflected light takes a longer duration to arrive at the left and right mirror ? A ''reflection dilation'' ?

11. ### DaveC426913Valued Senior Member

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The mirror is confusing you.
Looking at yourself in a mirror that is 2m away is optically identical to looking at your twin brother directly, standing 4m away.
When you look at someone standing 4m away, do you see - or expect to see - some sort of distortion?

12. ### DaveC426913Valued Senior Member

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Sure. Just like it takes longer for light to reach you from someone standing 4m away as from 2m away.
At 300,000km/s, how long a delay do you think 2m will be?

13. ### JerimiahRegistered Member

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I don't expect to see some sort of distortion looking at a person ! I am just finding it very difficult to see how the inverse square laws applies in regards to magnitude . I would of thought that light weakens over x rather than ^2 ?

14. ### JerimiahRegistered Member

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I think it would be very quick , to fast to notice with the eye .

15. ### JerimiahRegistered Member

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If the light becomes stretched out proportionally to the inverse , then why doesn't the reflection become stretched proportional ? Isn't the reflections characteristics ''laser like'' ? Except any angle ?

16. ### exchemistValued Senior Member

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I think your choice of the term "magnitude" may be confusing you. "Magnitude" could in principle refer to intensity (brightness), or size (physical dimensions). The term I used, also used in the Wiki article, is intensity. This means brightness. It is brightness that decreases with the square of distance from a source.

You would not expect the size of an image to be affected by the brightness of the light, would you?

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17. ### JerimiahRegistered Member

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Thank you , I think you have just cleared my confusion . I would not expect the size of the image to change but I now have an interesting test on optics .

If we constructed a massive mirror and placed it at one end of a runway , the other end having a commercial passenger plane :

1) The observer at the mirror end observes a full size plane in the mirror ?

2)The observer at the plane end observes a blur looking at the mirror ?

18. ### exchemistValued Senior Member

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Assuming it is a plane mirror (geddit?) i.e. flat:

1) An observer close to the mirror will see an image of the plane the same size as if he were to turn his head and look directly at the plane at the far end of the runway.

2) An observer at the plane end will see a reflection the same size as the first observer, but since he will be looking at it from the far end of the runway it will appear very small, as the distance is twice the length of the runway.

Bear in mind that the apparent size of objects is determined by the angle that light rays from the top and bottom make, as they enter your eye. That angle becomes smaller and smaller, the further the object, or image, is from your eye.

Janus is your go-to expert on this because he is an astronomer and they work with these angles all the time.

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19. ### JerimiahRegistered Member

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How sure of this are you ? Wouldn't the image in the mirror also show the scaling of distance between plane and mirror , making the plane look smaller in the mirror at the mirror end of the experiment ?

20. ### exchemistValued Senior Member

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Smaller than what, though? If the observer at the mirror end is up close to the mirror, he will see an image the same size (angular diameter) as if he looked at the plane itself. Of course, if he stands 100 meters away from the mirror, then the angular diameter will be smaller.

More on angular diameter (angular size) here: https://en.wikipedia.org/wiki/Angular_diameter

21. ### JerimiahRegistered Member

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Visually smaller than the plane is ?
I have a mirror here , I have just looked out of my window and there is two big aerials on a hill some distance away that visually look small . I look in the mirror with my back to the aerials , look in the mirror , they still look visually small !
If the aerials are reflecting their true size equal and proportional , then why are they small in my mirror ?

22. ### DaveC426913Valued Senior Member

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The perceived size of a distant object is derived from the angle it subtends in your field of view.

A mirror reflects the image, but does not change the angle it subtends.

I think drawing some diagrams - even simple ones - will help you.

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23. ### JerimiahRegistered Member

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Which is an opposite function of the inverse square law ?

A reflected image becomes more visual contracted the greater the distance the mirror is away ?