Mirror Definition and 654 Threads

A mirror is an object that reflects an image. Light that bounces off a mirror will show an image of whatever is in front of it, when focused through the lens of the eye or a camera. Mirrors reverse the direction of the image in an equal yet opposite angle from which the light shines upon it. This allows the viewer to see themselves or objects behind them, or even objects that are at an angle from them but out of their field of view, such as around a corner. Natural mirrors have existed since prehistoric times, such as the surface of water, but people have been manufacturing mirrors out of a variety of materials for thousands of years, like stone, metals, and glass. In modern mirrors, metals like silver or aluminum are often used due to their high reflectivity, applied as a thin coating on glass because of its naturally smooth and very hard surface.
A mirror is a wave reflector. Light consists of waves, and when light waves reflect off the flat surface of a mirror, those waves retain the same degree of curvature and vergence, in an equal yet opposite direction, as the original waves. The light can also be pictured as rays (imaginary lines radiating from the light source, that are always perpendicular to the waves). These rays are reflected at an equal yet opposite angle from which they strike the mirror (incident light). This property, called specular reflection, distinguishes a mirror from objects that diffuse light, breaking up the wave and scattering it in many directions (such as flat-white paint). Thus, a mirror can be any surface in which the texture or roughness of the surface is smaller (smoother) than the wavelength of the waves.
When looking at a mirror, one will see a mirror image or reflected image of objects in the environment, formed by light emitted or scattered by them and reflected by the mirror towards one's eyes. This effect gives the illusion that those objects are behind the mirror, or (sometimes) in front of it. When the surface is not flat, a mirror may behave like a reflecting lens. A plane mirror will yield a real-looking undistorted image, while a curved mirror may distort, magnify, or reduce the image in various ways, while keeping the lines, contrast, sharpness, colors, and other image properties intact.
A mirror is commonly used for inspecting oneself, such as during personal grooming; hence the old-fashioned name looking glass. This use, which dates from prehistory, overlaps with uses in decoration and architecture. Mirrors are also used to view other items that are not directly visible because of obstructions; examples include rear-view mirrors in vehicles, security mirrors in or around buildings, and dentist's mirrors. Mirrors are also used in optical and scientific apparatus such as telescopes, lasers, cameras, periscopes, and industrial machinery.
The terms "mirror" and "reflector" can be used for objects that reflect any other types of waves. An acoustic mirror reflects sound waves. Objects such as walls, ceilings, or natural rock-formations may produce echos, and this tendency often becomes a problem in acoustical engineering when designing houses, auditoriums, or recording studios. Acoustic mirrors may be used for applications such as parabolic microphones, atmospheric studies, sonar, and sea floor mapping. An atomic mirror reflects matter waves, and can be used for atomic interferometry and atomic holography.

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  1. N

    Does the Mirror Equation Apply to Parabolic Mirrors?

    I was wondering whether the curved surface mirror formula (that is usually used to solve convex or concave spherical mirror problems) remains unaltered in case of parabolic mirrors.What might be invalid is the equation 1/f= 2/R... After all,the equation 1/v + 1/u= 1/f pertains to...
  2. S

    Rubber stopper hanging from the view view mirror of a car

    Homework Statement A 18g rubber stopper is suspended by a 45-cm string from the rear view mirror of a car. As the car accelerates eastward, the string makes an angle of 5.1 degrees with the vertical. Determine the acceleration of the car. Homework Equations The Attempt at a...
  3. S

    Estimating image distance in lens and mirror

    I'm having difficulty understanding how to estimate the location of an image in a lens/mirror. I tried understanding it by going off the books question/answer section: "A spherical concave lens has a focal length of 16 cm, and an object is placed 8 cm from the lens." It says the answer is...
  4. K

    What is the Angle ϕ of the Reflected Laser Beam in Plane Mirror Reflection?

    Homework Statement A laser beam is incident on the left mirror in the figure below, in which α = 85°. Its initial direction is parallel to a line that bisects the mirrors. What is the angle ϕ of the reflected laser beam? http://www.webassign.net/knight/p23-40.gif" Homework Equations...
  5. L

    Curved mirror identification & magnification question

    Homework Statement I can't seem to figure out whether I'm dealing with a + or - radius value. Anyways here's the question: An object 5.0 cm tall produces an image that is 7.0 cm behind the mirror. If the radius of the curvature of this mirror is 10.0 cm, what is the magnification of the...
  6. R

    How Does a Rotating Mercury Tank Form a Parabolic Mirror?

    A concave astronomical telescope mirror may be made by rotating a circular tank of mercury. Find an expression for the shape of the surface in terms of the density of mercury, the radius from the centre and the rotaion rate so far I've come up with: KE=1/2MV^2 In the case of circular...
  7. nomadreid

    Appearance of new information: mirror of collapse?

    A lot has been written about the relative merits of decoherence versus the many-worlds theory in answering the question: where does the extra information go when a superposed state "collapses" to a definite state. However, what about the reverse: when the definite state returns to a new...
  8. S

    Travelling at speed of light and looking in the mirror

    suppose if you can travel at the speed of light. and you travel at the speed of light and look in the mirror can you see yourself in the mirror? people say you can but no one bothered to give me a explanation or they are just wrong i have no clue
  9. C

    Why Does Light Reflect Off a Mirror at the Same Angle It Hits?

    How come when light hits a mirror and then gets re-emitted , that the light comes off at the same angle it hits, when the light hits the glass or what-ever , when it interacts with the electrons in the atom , these electrons are orbiting so why can't they re-emit the light at some other angle .
  10. I

    Sunlight falls on a concave mirror, where is the image formed?

    Homework Statement Sunlight falls on a concave mirror and forms an image 3.0 cm from the mirror. If an object 24 mm high is placed 12.0 cm from the mirror, where will its image be formed? a. Use a ray diagram b. Use the lens/ mirror equation c. How high is the image? Homework Equations...
  11. J

    Parabola for 18 aluminum mirror

    Parabola for 18" aluminum mirror Help; need to configure inputs into parabola formula to machine an 18" dia., 1.5"h aluminum disc. for use as primary objective mirror in telescope.
  12. D

    Determining light intensity with a mirror

    Homework Statement You put a point source of light (S) a distance (d) in front of screen (A). How is the light intensity at the center of the screen changed if you put a completely reflecting mirror (M) a distance (d) behind the source? M-----d-----S-----d-----A Homework Equations...
  13. M

    How to Calculate Focal Length of a Convex Mirror?

    Homework Statement The virtual image produced by a convex mirror is one-quarter the size of the object. b) What is the focal length of this mirror? Homework Equations 1/di = 1/f - 1/do The Attempt at a Solution i found di to be -9.3 cm but when i solved for f i keep getting it...
  14. M

    Height of Mirror Needed to See Table in Mirror

    Homework Statement You are 1.9 m tall and stand 3.5 m from a plane mirror that extends vertically upward from the floor. On the floor 1.5 m in front of the mirror is a small table, 0.80 m high. a) What is the minimum height the mirror must have for you to be able to see the top of the...
  15. O

    How Do You Calculate Object-Image Separation for a Convex Mirror?

    Homework Statement A convex spherical mirror has a radius of curvature R = 20.0 cm and produces an upright image precisely one-quarter the size of an object. Calculate the separation distance between the object and its image? Homework Equations M = (image height)/(object height)...
  16. S

    How Much Can a 6ft Man See of His Image in a Mirror?

    A 6ft tall man stands in front of a mirror (2ft tall) The mirror is 5ft away from the man and 4 ft above the ground. How much of his image can he see? A 6ft tall man stands in front of a mirror (2ft tall) The mirror is 10 ft away from the man and 4 ft above the ground. How much of his...
  17. Q

    Relativity - Doppler effect in reflection from a moving mirror

    Homework Statement A plane mirror is moving at a uniform speed v away from the observer and a pulsing source of light of frequency f_0. What is the frequency of the light reflected in the mirror as seen by the observer? This isn't an actual homework question but I have a similar...
  18. H

    Image formed by concave mirror; completed need someone to check

    Homework Statement A person accidentally bit his tongue and wants to examine the bite by using a concave mirror. The mirror is placed 10 cm from the bite with the result that a virtual image of the bite appears 4 times actual size. Find the parameters s (distance from object to mirror), s'...
  19. A

    How can a mirror be front silvered or back silvered?

    Homework Statement Still I could not make the exact difference between the back silvered and the front silvered mirror. In many web sites only the method of making a back silvered mirror is given. My doubt is-"what makes the deposit back silvered or front silvered?". How will you say that...
  20. I

    Spoon Optics-Virtual Inverted image with a concave mirror

    When you look at a spoon, like at a mirror, the image of yourself appears to be on the other side of the mirror/spoon, where light does not go! So the image must be virtual! So tell me, since a concave mirror must produce a real inverted image when you are far from the focal point...
  21. C

    Photon Off a Mirror: How Does It Work?

    I was told today that when a photon hits the mirror it is absorbed by the atoms in the glass then reemitted by the matter , then I was told that the photon that is remitted can emit before the initial photon gets their . How does this work , Is it possible that the photon has magnetic field...
  22. P

    Is it possible to make a gravity mirror ?

    is it possible to make a "gravity mirror"? Does anyone out there know if under today's accepted laws of physics it would be possible for something to exist that could reflect gravity?. The reason I ask is because I am a bit of a late starter with this physics thing. I did schoolboy physics...
  23. E

    Is it possible to make a closed mirror system?

    Hello, my name is Edward Solomon, after much experimentation and calculation I have failed to make a system that can reflect light in a closed system. Now I am not naive enough to believe I can make a true closed system. There is an absorption and conversion to heat each time light strikes a...
  24. Z

    Paraxial approximation on concave mirror

    1. Find the length of the curvature of a concave mirror of 20cm that comply with paraxial approximation for all incident rays 2.conventional geometry formula , sinθ≈θ or tanθ≈θ for paraxial rays 3. I had try drafting out the diagram , labeling all the unknown angle with symbol and...
  25. R

    Mirror Optics- Measuring Virtual Image

    Recently, I asked my physics teacher how to measure the height of a virtual image behind a concave mirror. He said he wasn't exactly sure so he offered to give extra credit to anyone who could find information on how to do it. Is there anyone who can help?
  26. O

    Movable mirror of a Michelson interferometer

    i know the question may be a bit stupid to some people, but i seriously don't know how to do it... Homework Statement How far must the movable mirror of a Michelson interferometer, illuminated by a 589-nm source, be displaces for 2000 fringes to move past the reference point? Homework...
  27. P

    Rear view mirror and field of view

    A bus driver looks into a plane mirror 20 cm long which is placed 50 cm in front of him. If the rear window is 500 cm from the plane mirror, through what length of the rear window can he see whenever he looks into the mirror while driving? I have thought about this question but am...
  28. L

    Sound reflection & controversy in ray diagram of concave mirror

    I've two questions here:- 1) Sound reflects it is said using laws of reflection of light.So,it means we hear max. sound when angle of incidence is equal to angle of reflection,right?& if not equal then what do we hear or not? I guess we hear lesser than max.sound when the angles are not equal...
  29. turbo

    Raid1 or Mirror, software-based?

    I have two identical HDs in my PC and periodically, I back up from my primary drive to the slave to keep copies of modified files current. Is there anybody here using a software-based Raid or Mirroring solution to keep a HD duplicated in real-time (or perhaps batched overnight, etc)? I'll...
  30. V

    Calculating Multiple Images in a Plane Mirror

    Plane Mirror A person walks into a room that has, on opposite walls, two plane mirrors producing multiple images. Find the distances from the person to the first three images seen in the left-hand mirror when the person is 5ft from the mirror on the left wall and 10 ft from the mirror on the...
  31. N

    The Mystery of 99% Reflecting Mirrors: A Physics Perspective

    My professor today told us to think about the following situation: If there is a 99% reflecting mirror, then if a beam of light shines on the mirror 99% of the light is reflected and 1% is transmitted. Now he says that if a second 99% reflecting mirror is placed behind the original mirror, 100%...
  32. I

    One-Way Mirror Ball: Can it Collect Light?

    i had this thought a while ago and would like to have an answer i don't know whether or not this exists already so i thought i'd sign up and ask a forum, this is somewhat a what if question if a ball like object(more a ball with many sides don't know the technical name) was made out of a...
  33. M

    What Happens to Parallel Rays in Compound Lens and Mirror Setups?

    Homework Statement You have a thin lens with a concave and a convex side (let's say with radii r and R). You also have 2 mirrors, a convex one, that fits perfectly into the lens' concave side, and a concave one, that fits perfectly onto the lens' convex side (so the corresponding radii of...
  34. maverick280857

    Modification of Law of Reflection from a (moving) mirror in Special Relativity

    Hi everyone A few weeks ago, I had worked out the relations between the angle of reflection and angle of incidence in case of reflection from a plane mirror, (1) moving toward the incident ray (2) moving normal to the incident ray (PS -- This is not homework.) The way I did it was...
  35. J

    Cross hanging from rearview mirror

    A race-car driver is driving in a circle at a fixed velocity. He has a cross hanging down from a string on his rearview mirror. Which of the listed forces impacts the hanging cross as the driver drives around a circle at a fixed velocity? Gravity, Friction, Tension, and Centripetal Force I...
  36. vincentm

    Can I Make My Own Mirror for Astrophotography Using a 6in Blank?

    So one of my friends from my Astronomy club has given me a 6in mirror blank at our club mtg last week. I'd like to try my hand at making my own mirror. I didn't have time to stay and ask questions ( dropped into return an astronomy lecture vid to our library). How do i go about doing so? I'd...
  37. S

    Forces acting on object hanging from rearview mirror

    A string is hanging from the rearview mirror of you car and a ball is at the end of this string. Suppose that you drive around a circular track at fixed speed. Which list below gives all the forces that act on the ball? A) tension and the force of gravity b) tension force of gravity and...
  38. N

    Convex Mirror Image Distance and Magnification

    Homework Statement At an intersection of hospital hallways, a convex mirror is mounted high on a wall to help people avoid collisions. The mirror has a radius of curvature of 0.510 m. -What is the image distance for a patient 11.9 m from the mirror? (Use the correct sign conventions.)...
  39. 1

    Solving Spherical Mirror Homework: Focal Length & Point of Incidence

    Homework Statement In the attached picture , It has been explained in my book that " I the apeture of the mirror is small, the point P'( ponint of incidence) is very close to the point P( pole) ,Then PF(focal length)= P'F :. PF =Fc or PF=1/2R" I don't get it ! Plzzzz help!
  40. A

    Polygonal mirror reflection beam Problem

    Hello forum , i have a spindle motor from an HDD and i pasted to this motor 6 facets polygonal mirror, the problem is that the mirrors are not 100% alignment ( it's hand made) and the laser reflected from this mirrors is doing 6 lines ( where it should be one line if all mirrors are good...
  41. S

    Spherical Mirror and Object Distance

    If a spherical mirror has a radius of curvature of .24 m and and object is placed in front of it and magnified to twice its size: is the mirror concave, convex, or either? And what is the object's distance? I determined that the mirror was concave, because the question said that the image was...
  42. M

    Relative Velocity of running towards a mirror

    If you are running towards a mirror at 5m/sec, at what speed is your reflection moving towards you?
  43. F

    What gives objects their color?

    I've been pondering this for a while. 2 questions. The first question is how does a mirror work. Think about it, why and how does it reflect a near perfect image? My second question is why don't other things reflect light like mirrors do. More specifically, why doesn't a white piece of paper...
  44. M

    Is Muscle Memory tied to Mirror Neurons?

    Just wondering: I know that your mirror-neurons strengthen connections simply by watching someone perform an action. My question is, is muscle memory tied to mirror neurons? Or is this not yet known? Can you gain muscle memory simply by thinking about a certain motion, rather than...
  45. T

    Therefore, the focal length of the mirror is -1m.

    [SOLVED] Focal length of a mirror Homework Statement A 2.0-cm-tall object is placed in front of a mirror. A 1.0-cm-tall upright image is formed behind the mirror, 150 cm from the object. What is the focal length of the mirror? Homework Equations 1/f=1/s+1/s' m=h'/h m=-s'/s...
  46. K

    How does LLoyd's mirror works?

    I wonder how does Lloyd's mirror works, how does it produce the interference pattern? I look for many textbook, but all of them only tells the result and the setup without telling how to get the fringe and how to get the fringe separation. Anyone show me some hint or recommend me a book about...
  47. X

    Concave Mirror Experiment Question

    Homework Statement We did an experiment with a concave mirror. Concave mirror was placed on optics bench and a candle was placed at designated spots. A screen was used to see where the image was projected. When the object was placed between the focal point, image was not produced on the...
  48. L

    Quick and easy way to measure magnication of a concave mirror

    Hi, We're offered shaving mirrors by suppliers and sometimes their claims to the magnification are doubtful. I don't wish to upset any customers by giving incorrect information. So is there a practical way in which I can test the magnification myself? i.e. measuring the distance of the...
  49. D

    Optics and height of mirror problem

    Homework Statement A man is 160 cm tall and hiss eyes are 150 cm above the floor. He looks at his image formed by a plane mirror pleaced on a wall. Homework Equations a) In order to see his feet, what should the distance beetwen the bottom edge of the mirror and the floor be? b)To see...
  50. S

    Combining Lenses and Mirrors: Finding the Focal Length and Image Formation

    Homework Statement Question B only Homework Equations The Attempt at a Solution 1) Why we use f=15.0cm? Shouldn't it be f=infinity considering plane mirror have an infinity focal length? 2) Normally I do combination(lens, mirrors), firstly I will consider the front...
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