Thread: i dont understand how mirrors can reflect things

i was taught mirrors deflect light at the same angle they incide in the mirror since the mirror is perfectly flat

but thats false a mirror is far from being flat

at a microscopic level has valleys and mountains the size of the everest

so imagine im a microscopical cell with eyes that looks in a mirror at the reflection of a person

the mirror for me will be the size of earth and the human the size of the moon

but now the mirror has mountains and valleys the size of the everest

its just imposible i see the persons reflection with any definition at all

so if a cell cant see a reflection since theres huge mountain and valleys in the mirror so its far from being flat why can we?

a cell witheyes cant see a reflection but we can

come on this makes no sense mirrors got to be actually magical

Yes some of the light is not reflected back at the same angle, but only a tiny fraction. Not even remotely close to affecting its use as a household mirror. Its only when you start talking about how light behaves in a tiny microscopic patch of the mirror you will run into problems.

In large scale telescopes they spend months polishing mirrors to be as flat as possible exactly because they need to be flat on the microscopic scale. But for a household mirror I dont think you would notice that your reflection is not 100% (or even 70%).

They are relatively mostly smooth. The "mountains" you speak of would only mis-reflect a similarly sized portion of the light that hits it, i.e. minuscule.

but i dont think it matters the size of the mountains

what it matters its the angle of the surface

its just imposible to get 100% of surface at a 0º angle

if the mirror was like this \/\/\/\/\

even at the size of nanometres is virtually imposible it reflects images with the flat mirrors reflection laws

theres got to be somthing more going on, may be at perception level

Originally Posted by luxtpm

theres got to be somthing more going on, may be at perception level

CCD multipliers don't perceive.

Originally Posted by luxtpm

but i dont think it matters the size of the mountains

It does matter. Visible light has a wavelength of 390-750 nm. What this means is that light cannot detect or respond to imperfections in the surface smaller than this. If the imperfections are a few tens of nm in size, they don't exist as far as the light is concerned; They are just too small compared to the light's own wavelength.

It's like bouncing a basketball off a floor. As long as any imperfections in the floor's surface are small compared to surface area touching the floor, the ball doesn't care.

thanks a lot

theres something i still dont underatnd:

wavelenght of light seems to specify the thickness of the ray of light

but i thought that wavelenght was actually this:

if you drop a stone in water it will make waves

wavelenght is the distance between the different circular waves that appear in the water

so it has nothing to do with thickness

i think what would specify the thickness of the wave is actually called amplitude

anybody any light on this?

Wavelength is just that... its the length of the wave. Because waves are a simply an oscillating disturbance of a medium I'm not exactly sure that it makes sense to think of them with a thickness. I think in terms of bouncing off mirrors, perhaps it is the amplitude that keeps it from hitting at funny angles.

Originally Posted by luxtpm

thanks a lot

theres something i still dont underatnd:

wavelenght of light seems to specify the thickness of the ray of light

but i thought that wavelenght was actually this:

if you drop a stone in water it will make waves

wavelenght is the distance between the different circular waves that appear in the water

so it has nothing to do with thickness

i think what would specify the thickness of the wave is actually called amplitude

anybody any light on this?

It doesn't work to try and apply macroscopic classical physics examples to light, which at that scale behaves quantum mechanically. You are just not going to make any sense of it thinking classically. The wavelength of the photon is part of its wave function which determines the region over which the photon exists. The amplitude would just be the number of photons striking over a given time.

An example of limits imposed by wavelength is the waveguide. Fiber optic cable is a type of wave guide. You cannot pass light through a fiber optic cable that is smaller in diameter than the wavelength of the light, regardless of the amplitude of the wave.

This just the way light acts. To understand why light behaves this way takes a much deeper understanding of physics than you have displayed.

The amplitude would just be the number of photons striking over a given time.

If so, what's the amplitude of a single photon?

Originally Posted by mastermind

The amplitude would just be the number of photons striking over a given time.

If so, what's the amplitude of a single photon?

The energy of a photon is found by



where

h is the Planck constant
c is the speed of light
is the wavelength.

I believe the frequency would be related to the number of photons striking in a given time? If not, could you explain why the amplitude is?

Because just because the word wave is used doesn't mean it really has that much to do with what we think of when we think of waves (i.e. mechanical waves).

Originally Posted by JEllington

I believe the frequency would be related to the number of photons striking in a given time? If not, could you explain why the amplitude is?

Again, you are falling into the trap of trying to assign Classical macroscopic behavior to Quantum Mechanical effects.

Originally Posted by Janus

Originally Posted by JEllington

I believe the frequency would be related to the number of photons striking in a given time? If not, could you explain why the amplitude is?

Again, you are falling into the trap of trying to assign Classical macroscopic behavior to Quantum Mechanical effects.

So you still haven't told me why the amplitude (ie, height of the wave) gives information on how many photons are striking during a given time rather than the frequency (ie, period/second).

You're still using the wrong meaning of the word wave.

So, in quantum mechanics, a three dimensional wave of light's amplitude isn't the same as the classical one? Or do we just not describe waves in QM in the same ways we describe them classically (and that the amplitude has nothing to do with photons striking..)?

A wave in fysics is to time.

For instance if you,re at a canal watching the waves time going by, you don,t have to follow the wave running alongside the canal or even following a particular wave with you,re eyes.

A drawn wave-funktion with a horizontal axis for time, to keep up with time you would have to run along that line then, assumed you can only see the present not the future you would see an up and down movement of a point according to fysics. That,s the foton then, just going up, down, up, down, up ......it,s not a wave,its a funktion. If you would notmove fysically with time (fysically in the past) following time with you,re eyes covering the past and the future of the funktionline with eye caps as horses have you see also some ink (or not even that, just a geometrical point imagined being a particle) going up,down, up, down, up.

There are some similarities between the QM meaning of "wave" and the classical meaning of "wave", which is how it got the name in the first place, but they aren't the same thing. For one thing, a photon does not go "up, down, up, down, up, down."

I,m not saying anything about what a photon does just in general with a wave-funktion in fysics like a wave for electric voltage with time set out on a horizontal line and a fase of 1 second. The phase implies time ; a second. The funktion puts time as cm in the geometric representation giving it a size.

Looking at water-waves at sea or a canal you see the waves continous as you see the water continous and continous in motion áll the time.
Taking a picture of waves at sea you don,t need the time of a full phase to capture the whole wave on the photo, The shuttertime can be a split second. And the result is not a wave but a picture without the motion, it,s a frozen moment, rather dull.

For someone on a train letting a ping pong ball bounce up and down on a table it may seem not a typical wave, just up and down but for someone who sees the train with the bouncing ball pass it becomes a wave....so what,s a wave and what's just bouncing up and down ? It,s relative.

For the mirror the frecquency does not determine a size for a photon (time put in to cm,s) if a photon is considered a point it,s a point for all frecquency's and it has not a size. Only funktions in fysics are made visible by transformingtime into a fysical distance. Not understanding that it becomes illusionary, time and length (or distance become mixed up) time as a dimension does not mean that it is a distance in the fysical sense.

Originally Posted by JEllington

Originally Posted by Janus

Originally Posted by JEllington

I believe the frequency would be related to the number of photons striking in a given time? If not, could you explain why the amplitude is?

Again, you are falling into the trap of trying to assign Classical macroscopic behavior to Quantum Mechanical effects.

So you still haven't told me why the amplitude (ie, height of the wave) gives information on how many photons are striking during a given time rather than the frequency (ie, period/second).

This is kind of complicated to explain. The frequency is a property each individual photon has. For example, if you see a beam of 600 nanometer (red) light, what this means is each and every photon in that beam individually has a 600 nm wavelength. If the beam is really bright (has a high amplitude), that means there are a lot of these 600 nm photons.

A photon is kind of like a particle, but kind of like a wave. It acts like a wave even if there's only one photon. The unwave-like trait is that it always lands in exactly one place, instead of exerting pressure on a wide area.

This is kind of complicated to explain. The frequency is a property each individual photon has.

It,s allready difficult as to how frecquency can be a property. I have always understood frecquencies as ratio between two events,rhytms, durations. In fysics the second is a standard to compare other rhytms and events to.

In daily live the use is more free like the frecquency of going to the toilet each day.
The amount of hollidays per year is a frecquency also only bit less evenly spread.

As a ratio number frecquency can,t be a property of something.
In the above cases the frequency would be a property of easch visit to the bathroom and each holliday.

With dancers or musicians also the frecquency (maybe even the rhytm) is not a property of the dancers or musicians it,s more like a property of the music and
dance.

I may not be allowed to compare photons with dancers but it says something about the meaning, notion and use of frequencies in general.

Then when a photon is a particle ánd considered a geometrical point how can rhytm be a property of a point ? The frequency I can imagine telling something about the secquency, distance in time between two fotons (and related to the distance between two seconds (as coordinates) but still not a property of a single photon.

http://www.youtube.com/watch?v=DfPeprQ7oGc
Light acts as a wave and a particle. Getting off topic here, but it's very interesting.

i just bought a shinny hammer, it has ondulations bigger than a tenth of milimiter that i can see with the naked eye

still it reflects images almost perfectly

with such ondulations i dont understant how it can reflect a thing applying the optics laws

Almost perfectly to the human eye doesn't mean a whole lot. Those ripples are too big to scatter the light, but small enough that the distortions they create aren't entirely obvious to the human eye. If you looked at the reflected image of a bright light, it'd be more obvious.

Another related quite fascinating thing is hpw you can look into a microwave oven, but the microwave radiation can't pass through the window. This because of the grating on the window, the small holes (1-2 mm) are large enough for visible light to pass through, but too small for the microwave radiation to come through. Microwaves having a wavelength of approx 12 cm.

Same thing, only this time it's on a scale we can see. We can easily see through the holes, but microwaves can not get through.